Major Refactor - Static constants and test case names

src/function/UserDefinedFunction.java

@@ -1,6 +1,7 @@
 package function;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Nil.NIL;
 
 import java.text.MessageFormat;
 import java.util.ArrayList;
@@ -113,7 +114,7 @@ public class UserDefinedFunction extends LispFunction {
     }
 
     private SExpression evaluateBody() {
-        SExpression lastEvaluation = Nil.getInstance();
+        SExpression lastEvaluation = NIL;
 
         for (Cons expression = body; expression.isCons(); expression = (Cons) expression.getRest())
             lastEvaluation = eval(expression.getFirst());

src/function/builtin/EVAL.java

@@ -1,5 +1,8 @@
 package function.builtin;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import java.text.MessageFormat;
 
 import error.LispException;
@@ -32,9 +35,9 @@ public class EVAL extends LispFunction {
 
     public static SExpression lookupSymbol(String symbolName) {
         if (symbolName.equals("NIL"))
-            return Nil.getInstance();
+            return NIL;
         else if (symbolName.equals("T"))
-            return Symbol.T;
+            return T;
         else if (symbolName.startsWith(":"))
             return new Symbol(symbolName);
 
@@ -97,7 +100,7 @@ public class EVAL extends LispFunction {
 
     private Cons evaluateArgList(Cons arguments) {
         if (arguments.isNull())
-            return Nil.getInstance();
+            return NIL;
 
         SExpression first = eval(arguments.getFirst());
         SExpression rest = arguments.getRest();

src/function/builtin/EXIT.java

@@ -1,5 +1,7 @@
 package function.builtin;
 
+import static sexpression.Nil.NIL;
+
 import environment.RuntimeEnvironment;
 import function.*;
 import sexpression.*;
@@ -20,7 +22,7 @@ public class EXIT extends LispFunction {
         argumentValidator.validate(argumentList);
         environment.terminateSuccessfully();
 
-        return Nil.getInstance();
+        return NIL;
     }
 
 }

src/function/builtin/LOAD.java

@@ -1,6 +1,8 @@
 package function.builtin;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import java.io.*;
 import java.text.MessageFormat;
@@ -44,7 +46,7 @@ public class LOAD extends LispFunction {
         if (parser != null)
             wasSuccessful = isSuccessfulEvaluation(parser);
 
-        return wasSuccessful ? Symbol.T : Nil.getInstance();
+        return wasSuccessful ? T : NIL;
     }
 
     private LispParser attemptToCreateParserOnFile(String fileName) {

src/function/builtin/cons/LIST.java

@@ -1,5 +1,7 @@
 package function.builtin.cons;
 
+import static sexpression.Nil.NIL;
+
 import function.*;
 import sexpression.*;
 
@@ -13,7 +15,7 @@ public class LIST extends LispFunction {
     }
 
     public static Cons makeList(SExpression sexpr) {
-        return new Cons(sexpr, Nil.getInstance());
+        return new Cons(sexpr, NIL);
     }
 
     public Cons call(Cons argumentList) {
@@ -24,7 +26,7 @@ public class LIST extends LispFunction {
 
     private Cons callRecursive(Cons argumentList) {
         if (argumentList.isNull())
-            return Nil.getInstance();
+            return NIL;
 
         SExpression firstArgument = argumentList.getFirst();
         Cons remainingArguments = (Cons) argumentList.getRest();

src/function/builtin/math/MULTIPLY.java

@@ -1,5 +1,7 @@
 package function.builtin.math;
 
+import static sexpression.LispNumber.ONE;
+
 import function.*;
 import sexpression.*;
 
@@ -18,7 +20,7 @@ public class MULTIPLY extends LispFunction {
     public LispNumber call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return mathFunction.callTailRecursive(new Cons(LispNumber.ONE, argumentList));
+        return mathFunction.callTailRecursive(new Cons(ONE, argumentList));
     }
 
     private LispNumber multiply(LispNumber number1, LispNumber number2) {

src/function/builtin/math/PLUS.java

@@ -1,5 +1,7 @@
 package function.builtin.math;
 
+import static sexpression.LispNumber.ZERO;
+
 import function.*;
 import sexpression.*;
 
@@ -18,7 +20,7 @@ public class PLUS extends LispFunction {
     public LispNumber call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return mathFunction.callTailRecursive(new Cons(LispNumber.ZERO, argumentList));
+        return mathFunction.callTailRecursive(new Cons(ZERO, argumentList));
     }
 
     private LispNumber add(LispNumber number1, LispNumber number2) {

src/function/builtin/predicate/ATOM.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -17,7 +20,7 @@ public class ATOM extends LispFunction {
         argumentValidator.validate(argumentList);
         SExpression argument = argumentList.getFirst();
 
-        return argument.isAtom() ? Symbol.T : Nil.getInstance();
+        return argument.isAtom() ? T : NIL;
     }
 
 }

src/function/builtin/predicate/EQ.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -35,7 +38,7 @@ public class EQ extends LispFunction {
     }
 
     private SExpression atomEq(SExpression firstArgument, SExpression secondArgument) {
-        return isEq(firstArgument, secondArgument) ? Symbol.T : Nil.getInstance();
+        return isEq(firstArgument, secondArgument) ? T : NIL;
     }
 
     private boolean isEq(SExpression firstArgument, SExpression secondArgument) {
@@ -43,7 +46,7 @@ public class EQ extends LispFunction {
     }
 
     private SExpression listEq(SExpression firstArgument, SExpression secondArgument) {
-        return (firstArgument == secondArgument) ? Symbol.T : Nil.getInstance();
+        return (firstArgument == secondArgument) ? T : NIL;
     }
 
 }

src/function/builtin/predicate/EQUAL.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -28,7 +31,7 @@ public class EQUAL extends LispFunction {
     }
 
     private SExpression equal(SExpression firstArgument, SExpression secondArgument) {
-        return isEqual(firstArgument, secondArgument) ? Symbol.T : Nil.getInstance();
+        return isEqual(firstArgument, secondArgument) ? T : NIL;
     }
 
 }

src/function/builtin/predicate/LISTP.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -16,7 +19,7 @@ public class LISTP extends LispFunction {
     public SExpression call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return argumentList.getFirst().isList() ? Symbol.T : Nil.getInstance();
+        return argumentList.getFirst().isList() ? T : NIL;
     }
 
 }

src/function/builtin/predicate/NULL.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -16,7 +19,7 @@ public class NULL extends LispFunction {
     public SExpression call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return argumentList.getFirst().isNull() ? Symbol.T : Nil.getInstance();
+        return argumentList.getFirst().isNull() ? T : NIL;
     }
 
 }

src/function/builtin/predicate/NUMERIC_EQUAL.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -24,7 +27,7 @@ public class NUMERIC_EQUAL extends LispFunction {
         Cons remainingArguments = (Cons) argumentList.getRest();
 
         if (remainingArguments.isNull())
-            return Symbol.T;
+            return T;
 
         SExpression firstArgument = argumentList.getFirst();
         LispNumber number1 = (LispNumber) firstArgument;
@@ -32,7 +35,7 @@ public class NUMERIC_EQUAL extends LispFunction {
         LispNumber number2 = (LispNumber) secondArgument;
 
         if (!isEqual(number1, number2))
-            return Nil.getInstance();
+            return NIL;
 
         return callTailRecursive(remainingArguments);
     }

src/function/builtin/predicate/NUMERIC_GREATER.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -24,7 +27,7 @@ public class NUMERIC_GREATER extends LispFunction {
         Cons remainingArguments = (Cons) argumentList.getRest();
 
         if (remainingArguments.isNull())
-            return Symbol.T;
+            return T;
 
         SExpression firstArgument = argumentList.getFirst();
         SExpression secondArgument = remainingArguments.getFirst();
@@ -32,7 +35,7 @@ public class NUMERIC_GREATER extends LispFunction {
         LispNumber number2 = (LispNumber) secondArgument;
 
         if (!isFirstGreater(number1, number2))
-            return Nil.getInstance();
+            return NIL;
 
         return callTailRecursive(remainingArguments);
     }

src/function/builtin/predicate/NUMERIC_LESS.java

@@ -1,5 +1,8 @@
 package function.builtin.predicate;
 
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
+
 import function.*;
 import sexpression.*;
 
@@ -24,7 +27,7 @@ public class NUMERIC_LESS extends LispFunction {
         Cons remainingArguments = (Cons) argumentList.getRest();
 
         if (remainingArguments.isNull())
-            return Symbol.T;
+            return T;
 
         SExpression firstArgument = argumentList.getFirst();
         SExpression secondArgument = remainingArguments.getFirst();
@@ -32,7 +35,7 @@ public class NUMERIC_LESS extends LispFunction {
         LispNumber number2 = (LispNumber) secondArgument;
 
         if (!isFirstLesser(number1, number2))
-            return Nil.getInstance();
+            return NIL;
 
         return callTailRecursive(remainingArguments);
     }

src/function/builtin/special/AND.java

@@ -1,6 +1,7 @@
 package function.builtin.special;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Symbol.T;
 
 import function.*;
 import sexpression.*;
@@ -17,7 +18,7 @@ public class AND extends LispSpecialFunction {
     public SExpression call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return callTailRecursive(argumentList, Symbol.T);
+        return callTailRecursive(argumentList, T);
     }
 
     private SExpression callTailRecursive(Cons argumentList, SExpression lastValue) {

src/function/builtin/special/CASE.java

@@ -2,6 +2,8 @@ package function.builtin.special;
 
 import static function.builtin.EVAL.eval;
 import static function.builtin.predicate.EQUAL.isEqual;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import function.*;
 import sexpression.*;
@@ -27,7 +29,7 @@ public class CASE extends LispSpecialFunction {
 
     private SExpression callTailRecursive(SExpression key, Cons argumentList) {
         if (argumentList.isNull())
-            return Nil.getInstance();
+            return NIL;
 
         Cons clause = (Cons) argumentList.getFirst();
         Cons remainingClauses = (Cons) argumentList.getRest();
@@ -57,7 +59,7 @@ public class CASE extends LispSpecialFunction {
     }
 
     private boolean isKeyListT(SExpression keyList) {
-        return isEqual(Symbol.T, keyList);
+        return isEqual(T, keyList);
     }
 
     private SExpression advanceCons(SExpression knownCons) {
@@ -69,7 +71,7 @@ public class CASE extends LispSpecialFunction {
     }
 
     private SExpression evaluateConsequents(SExpression consequentList) {
-        SExpression lastConsequentValue = Nil.getInstance();
+        SExpression lastConsequentValue = NIL;
 
         for (; consequentList.isCons(); consequentList = advanceCons(consequentList))
             lastConsequentValue = eval(getFirst(consequentList));

src/function/builtin/special/COND.java

@@ -1,6 +1,7 @@
 package function.builtin.special;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Nil.NIL;
 
 import function.*;
 import sexpression.*;
@@ -24,7 +25,7 @@ public class COND extends LispSpecialFunction {
 
     private SExpression callTailRecursive(Cons argumentList) {
         if (argumentList.isNull())
-            return Nil.getInstance();
+            return NIL;
 
         Cons clause = (Cons) argumentList.getFirst();
         Cons remainingClauses = (Cons) argumentList.getRest();
@@ -37,7 +38,7 @@ public class COND extends LispSpecialFunction {
     }
 
     private boolean isTestSuccessful(SExpression test) {
-        return test != Nil.getInstance();
+        return test != NIL;
     }
 
     private SExpression evaluateConsequents(SExpression consequentList, SExpression test) {

src/function/builtin/special/LET.java

@@ -1,6 +1,7 @@
 package function.builtin.special;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Nil.NIL;
 
 import function.*;
 import sexpression.*;
@@ -71,7 +72,7 @@ public class LET extends LispSpecialFunction {
     }
 
     private SExpression evaluateBody(Cons body) {
-        SExpression lastEvaluation = Nil.getInstance();
+        SExpression lastEvaluation = NIL;
 
         for (; body.isCons(); body = (Cons) body.getRest())
             lastEvaluation = eval(body.getFirst());

src/function/builtin/special/PROGN.java

@@ -1,6 +1,7 @@
 package function.builtin.special;
 
 import static function.builtin.EVAL.eval;
+import static sexpression.Nil.NIL;
 
 import function.*;
 import sexpression.*;
@@ -17,7 +18,7 @@ public class PROGN extends LispSpecialFunction {
     public SExpression call(Cons argumentList) {
         argumentValidator.validate(argumentList);
 
-        return callTailRecursive(argumentList, Nil.getInstance());
+        return callTailRecursive(argumentList, NIL);
     }
 
     private SExpression callTailRecursive(Cons argumentList, SExpression lastValue) {

src/sexpression/Nil.java

@@ -3,11 +3,7 @@ package sexpression;
 @DisplayName("nil")
 public class Nil extends Cons {
 
-    private static Nil uniqueInstance = new Nil();
+    public static final Nil NIL = new Nil();
-
-    public static Nil getInstance() {
-        return uniqueInstance;
-    }
 
     private Nil() {
         super(null, null);

src/token/QuoteMark.java

@@ -1,5 +1,7 @@
 package token;
 
+import static sexpression.Nil.NIL;
+
 import java.util.function.Supplier;
 
 import file.FilePosition;
@@ -16,7 +18,7 @@ public class QuoteMark extends Token {
         Token nextToken = getNextToken.get();
         SExpression argument = nextToken.parseSExpression(getNextToken);
 
-        return new Cons(Symbol.createQuote(), new Cons(argument, Nil.getInstance()));
+        return new Cons(Symbol.createQuote(), new Cons(argument, NIL));
     }
 
 }

src/token/RightParenthesis.java

@@ -1,10 +1,12 @@
 package token;
 
+import static sexpression.Nil.NIL;
+
 import java.util.function.Supplier;
 
 import error.LineColumnException;
 import file.FilePosition;
-import sexpression.*;
+import sexpression.SExpression;
 
 public class RightParenthesis extends Token {
 
@@ -19,7 +21,7 @@ public class RightParenthesis extends Token {
 
     @Override
     public SExpression parseSExpressionTail(Supplier<Token> getNextToken) {
-        return Nil.getInstance();
+        return NIL;
     }
 
     public static class StartsWithRightParenthesisException extends LineColumnException {

test/function/ArgumentValidatorTester.java

@@ -2,6 +2,8 @@ package function;
 
 import static error.ErrorManager.Severity.ERROR;
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import org.junit.*;
 
@@ -13,10 +15,10 @@ public class ArgumentValidatorTester {
     private ArgumentValidator validator;
 
     private Cons makeArgumentListOfSize(int size) {
-        Cons argumentList = Nil.getInstance();
+        Cons argumentList = NIL;
 
         for (int i = 0; i < size; i++)
-            argumentList = new Cons(Nil.getInstance(), argumentList);
+            argumentList = new Cons(NIL, argumentList);
 
         return argumentList;
     }
@@ -73,14 +75,14 @@ public class ArgumentValidatorTester {
 
     @Test
     public void tooManyArgumentsException_HasCorrectSeverity() {
-        TooManyArgumentsException e = new TooManyArgumentsException("TEST", Nil.getInstance());
+        TooManyArgumentsException e = new TooManyArgumentsException("TEST", NIL);
 
         assertEquals(ERROR, e.getSeverity());
     }
 
     @Test
     public void tooManyArgumentsException_HasMessageText() {
-        TooManyArgumentsException e = new TooManyArgumentsException("TEST", Nil.getInstance());
+        TooManyArgumentsException e = new TooManyArgumentsException("TEST", NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);
@@ -88,14 +90,14 @@ public class ArgumentValidatorTester {
 
     @Test
     public void tooFewArgumentsException_HasCorrectSeverity() {
-        TooFewArgumentsException e = new TooFewArgumentsException("TEST", Nil.getInstance());
+        TooFewArgumentsException e = new TooFewArgumentsException("TEST", NIL);
 
         assertEquals(ERROR, e.getSeverity());
     }
 
     @Test
     public void tooFewArgumentsException_HasMessageText() {
-        TooFewArgumentsException e = new TooFewArgumentsException("TEST", Nil.getInstance());
+        TooFewArgumentsException e = new TooFewArgumentsException("TEST", NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);
@@ -103,14 +105,14 @@ public class ArgumentValidatorTester {
 
     @Test
     public void BadArgumentTypeException_HasCorrectSeverity() {
-        BadArgumentTypeException e = new BadArgumentTypeException("TEST", Nil.getInstance(), SExpression.class);
+        BadArgumentTypeException e = new BadArgumentTypeException("TEST", NIL, SExpression.class);
 
         assertEquals(ERROR, e.getSeverity());
     }
 
     @Test
     public void BadArgumentTypeException_HasMessageText() {
-        BadArgumentTypeException e = new BadArgumentTypeException("TEST", Nil.getInstance(), SExpression.class);
+        BadArgumentTypeException e = new BadArgumentTypeException("TEST", NIL, SExpression.class);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);
@@ -130,7 +132,7 @@ public class ArgumentValidatorTester {
 
     @Test
     public void correctFirstAndRestArgumentTypes_DoesNotThrowException() {
-        Cons argumentList = new Cons(Symbol.T, new Cons(Nil.getInstance(), Nil.getInstance()));
+        Cons argumentList = new Cons(T, new Cons(NIL, NIL));
 
         validator.setFirstArgumentExpectedType(Symbol.class);
         validator.setTrailingArgumentExpectedType(Cons.class);
@@ -139,7 +141,7 @@ public class ArgumentValidatorTester {
 
     @Test(expected = BadArgumentTypeException.class)
     public void badFirstArgumentType_ThrowsException() {
-        Cons argumentList = new Cons(Symbol.T, new Cons(Nil.getInstance(), Nil.getInstance()));
+        Cons argumentList = new Cons(T, new Cons(NIL, NIL));
 
         validator.setFirstArgumentExpectedType(Cons.class);
         validator.setTrailingArgumentExpectedType(Cons.class);
@@ -148,7 +150,7 @@ public class ArgumentValidatorTester {
 
     @Test(expected = BadArgumentTypeException.class)
     public void badTrailingArgumentType_ThrowsException() {
-        Cons argumentList = new Cons(Symbol.T, new Cons(Nil.getInstance(), Nil.getInstance()));
+        Cons argumentList = new Cons(T, new Cons(NIL, NIL));
 
         validator.setFirstArgumentExpectedType(Symbol.class);
         validator.setTrailingArgumentExpectedType(Symbol.class);
@@ -157,7 +159,7 @@ public class ArgumentValidatorTester {
 
     @Test
     public void expectedTypeWithNoDisplayName_DoesNotCauseNPE() {
-        Cons argumentList = new Cons(Symbol.T, new Cons(Nil.getInstance(), Nil.getInstance()));
+        Cons argumentList = new Cons(T, new Cons(NIL, NIL));
         SExpression withoutDisplayName = new SExpression() {};
 
         validator.setEveryArgumentExpectedType(withoutDisplayName.getClass());
@@ -172,28 +174,28 @@ public class ArgumentValidatorTester {
 
     @Test(expected = DottedArgumentListException.class)
     public void givenDottedArgumentList_ThrowsException() {
-        Cons argumentList = new Cons(Symbol.T, Symbol.T);
+        Cons argumentList = new Cons(T, T);
 
         validator.validate(argumentList);
     }
 
     @Test(expected = DottedArgumentListException.class)
     public void givenLargeDottedArgumentList_ThrowsException() {
-        Cons argumentList = new Cons(Symbol.T, new Cons(Symbol.T, Symbol.T));
+        Cons argumentList = new Cons(T, new Cons(T, T));
 
         validator.validate(argumentList);
     }
 
     @Test
     public void DottedArgumentListException_HasCorrectSeverity() {
-        DottedArgumentListException e = new DottedArgumentListException("TEST", Nil.getInstance());
+        DottedArgumentListException e = new DottedArgumentListException("TEST", NIL);
 
         assertEquals(ERROR, e.getSeverity());
     }
 
     @Test
     public void dottedArgumentListException_HasMessageText() {
-        DottedArgumentListException e = new DottedArgumentListException("TEST", Nil.getInstance());
+        DottedArgumentListException e = new DottedArgumentListException("TEST", NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);
@@ -202,19 +204,19 @@ public class ArgumentValidatorTester {
     @Test(expected = BadArgumentTypeException.class)
     public void doNotAcceptNil_ThrowsExceptionOnNilArgument() {
         validator.doNotAcceptNil();
-        validator.validate(new Cons(Symbol.T, new Cons(Nil.getInstance(), Nil.getInstance())));
+        validator.validate(new Cons(T, new Cons(NIL, NIL)));
     }
 
     @Test
     public void doNotAcceptNil_AllowsEmptyArgumentList() {
         validator.doNotAcceptNil();
-        validator.validate(Nil.getInstance());
+        validator.validate(NIL);
     }
 
     @Test
     public void doNotAcceptNil_AllowsProperList() {
         validator.doNotAcceptNil();
-        validator.validate(new Cons(Symbol.T, new Cons(Symbol.T, Nil.getInstance())));
+        validator.validate(new Cons(T, new Cons(T, NIL)));
     }
 
 }

test/function/UserDefinedFunctionTester.java

@@ -1,6 +1,7 @@
 package function;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
 import static testutil.TestUtilities.assertSExpressionsMatch;
 
 import org.junit.Test;
@@ -15,27 +16,24 @@ public class UserDefinedFunctionTester {
     private static final String FUNCTION_NAME = "TEST";
 
     private UserDefinedFunction createNoArgumentFunctionThatReturnsNil() {
-        return new UserDefinedFunction(FUNCTION_NAME, Nil.getInstance(),
+        return new UserDefinedFunction(FUNCTION_NAME, NIL, new Cons(NIL, NIL));
-                                       new Cons(Nil.getInstance(), Nil.getInstance()));
     }
 
     private UserDefinedFunction createOneArgumentFunctionThatReturnsArgument() {
-        return new UserDefinedFunction(FUNCTION_NAME, new Cons(new Symbol("X"), Nil.getInstance()),
+        return new UserDefinedFunction(FUNCTION_NAME, new Cons(new Symbol("X"), NIL), new Cons(new Symbol("X"), NIL));
-                                       new Cons(new Symbol("X"), Nil.getInstance()));
     }
 
     @Test
     public void nilFunctionCall() {
         UserDefinedFunction function = createNoArgumentFunctionThatReturnsNil();
 
-        assertEquals(Nil.getInstance(), function.call(Nil.getInstance()));
+        assertEquals(NIL, function.call(NIL));
     }
 
     @Test
     public void nilFunctionToString() {
         UserDefinedFunction function = createNoArgumentFunctionThatReturnsNil();
-        Cons expected = new Cons(new Symbol(FUNCTION_NAME),
+        Cons expected = new Cons(new Symbol(FUNCTION_NAME), new Cons(NIL, new Cons(NIL, NIL)));
-                                 new Cons(Nil.getInstance(), new Cons(Nil.getInstance(), Nil.getInstance())));
 
         assertSExpressionsMatch(expected, function.getLambdaExpression());
     }
@@ -44,7 +42,7 @@ public class UserDefinedFunctionTester {
     public void oneArgumentFunction_ReturnsCorrectValue() {
         UserDefinedFunction function = createOneArgumentFunctionThatReturnsArgument();
         SExpression argument = new LispNumber("23");
-        Cons argumentList = new Cons(argument, Nil.getInstance());
+        Cons argumentList = new Cons(argument, NIL);
 
         assertSExpressionsMatch(argument, function.call(argumentList));
     }
@@ -53,7 +51,7 @@ public class UserDefinedFunctionTester {
     public void oneArgumentFunction_ThrowsExceptionWithTooManyArguments() {
         UserDefinedFunction function = createOneArgumentFunctionThatReturnsArgument();
         SExpression argument = new LispNumber("23");
-        Cons argumentList = new Cons(argument, new Cons(argument, Nil.getInstance()));
+        Cons argumentList = new Cons(argument, new Cons(argument, NIL));
 
         function.call(argumentList);
     }
@@ -62,13 +60,12 @@ public class UserDefinedFunctionTester {
     public void oneArgumentFunction_ThrowsExceptionWithTooFewArguments() {
         UserDefinedFunction function = createOneArgumentFunctionThatReturnsArgument();
 
-        function.call(Nil.getInstance());
+        function.call(NIL);
     }
 
     @Test
     public void illegalKeywordRestPositionException_HasCorrectAttributes() {
-        IllegalKeywordRestPositionException e = new IllegalKeywordRestPositionException(FUNCTION_NAME,
+        IllegalKeywordRestPositionException e = new IllegalKeywordRestPositionException(FUNCTION_NAME, NIL);
-                                                                                        Nil.getInstance());
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);

test/function/builtin/APPLYTester.java

@@ -1,5 +1,6 @@
 package function.builtin;
 
+import static function.builtin.APPLY.apply;
 import static testutil.TestUtilities.*;
 
 import org.junit.Test;
@@ -11,56 +12,56 @@ import sexpression.Cons;
 public class APPLYTester {
 
     @Test
-    public void testApply() {
+    public void applyWithSymbol() {
         String input = "(apply '+ '(1 2 3))";
 
         assertSExpressionsMatch(parseString("6"), evaluateString(input));
     }
 
     @Test
-    public void testApplyWithLambdaExpression() {
+    public void applyWithLambdaExpression() {
         String input = "(apply (lambda (x) (+ x 1)) '(25))";
 
         assertSExpressionsMatch(parseString("26"), evaluateString(input));
     }
 
     @Test
-    public void testApplyWithQuotedLambdaExpression() {
+    public void applyWithQuotedLambdaExpression() {
         String input = "(apply '(lambda (x) (+ x 1)) '(25))";
 
         assertSExpressionsMatch(parseString("26"), evaluateString(input));
     }
 
     @Test
-    public void testStaticApplyCall() {
+    public void staticApplyCall() {
         String argumentList = "(+ (25 10))";
         Cons parsedArgumentList = (Cons) parseString(argumentList);
 
-        assertSExpressionsMatch(parseString("35"), APPLY.apply(parsedArgumentList));
+        assertSExpressionsMatch(parseString("35"), apply(parsedArgumentList));
     }
 
     @Test(expected = UndefinedFunctionException.class)
-    public void testApplyWithUndefinedFunction() {
+    public void applyWithUndefinedFunction() {
         evaluateString("(apply 'f '(1 2 3))");
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testApplyWithNonListSecondArgument() {
+    public void applyWithNonListSecondArgument() {
         evaluateString("(apply '+ '2)");
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testApplyWithTooManyArguments() {
+    public void applyWithTooManyArguments() {
         evaluateString("(apply '1 '2 '3)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testApplyWithTooFewArguments() {
+    public void applyWithTooFewArguments() {
         evaluateString("(apply '1)");
     }
 
     @Test(expected = DottedArgumentListException.class)
-    public void testCondWithDottedArgumentList_ThrowsException() {
+    public void applyWithDottedArgumentList_ThrowsException() {
         evaluateString("(apply 'apply (cons 'T 'T))");
     }
 

test/function/builtin/EVALTester.java

@@ -1,87 +1,88 @@
 package function.builtin;
 
+import static function.builtin.EVAL.lookupSymbol;
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
 import static testutil.TestUtilities.*;
 
 import org.junit.Test;
 
 import function.ArgumentValidator.*;
 import function.builtin.EVAL.*;
-import sexpression.Nil;
 
 public class EVALTester {
 
     @Test
-    public void testEval() {
+    public void evalNumber() {
         String input = "(eval 9)";
 
         assertSExpressionsMatch(parseString("9"), evaluateString(input));
     }
 
     @Test
-    public void testEvalNil() {
+    public void evalNil() {
         String input = "(eval ())";
 
         assertSExpressionsMatch(parseString("()"), evaluateString(input));
     }
 
     @Test
-    public void testLookupSymbol() {
+    public void lookupKeywordSymbol() {
         String symbol = ":symbol";
-        assertSExpressionsMatch(parseString(symbol), EVAL.lookupSymbol(symbol));
+        assertSExpressionsMatch(parseString(symbol), lookupSymbol(symbol));
     }
 
     @Test
-    public void testLookupT() {
+    public void lookupT() {
         String symbol = "T";
-        assertSExpressionsMatch(parseString(symbol), EVAL.lookupSymbol(symbol));
+        assertSExpressionsMatch(parseString(symbol), lookupSymbol(symbol));
     }
 
     @Test
-    public void testLookupNil() {
+    public void lookupNil() {
         String symbol = "NIL";
-        assertSExpressionsMatch(parseString(symbol), EVAL.lookupSymbol(symbol));
+        assertSExpressionsMatch(parseString(symbol), lookupSymbol(symbol));
     }
 
     @Test
-    public void testLookupUndefinedSymbol() {
+    public void lookupUndefinedSymbol() {
         assertNull(EVAL.lookupSymbol("undefined"));
     }
 
     @Test(expected = UndefinedFunctionException.class)
-    public void testEvalUndefinedFunction() {
+    public void evalUndefinedFunction() {
         String input = "(funcall 'eval '(undefined))";
 
         evaluateString(input);
     }
 
     @Test(expected = UndefinedSymbolException.class)
-    public void testEvalUndefinedSymbol() {
+    public void evalUndefinedSymbol() {
         String input = "(eval undefined)";
 
         evaluateString(input);
     }
 
     @Test(expected = DottedArgumentListException.class)
-    public void testEvalWithDottedLambdaList() {
+    public void evalWithDottedLambdaList() {
         String input = "(funcall 'eval (cons '+ 1))";
 
         evaluateString(input);
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testEvalWithTooManyArguments() {
+    public void evalWithTooManyArguments() {
         evaluateString("(eval '1 '2 '3)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testEvalWithTooFewArguments() {
+    public void evalWithTooFewArguments() {
         evaluateString("(eval)");
     }
 
     @Test
     public void undefinedFunctionException_HasMessageText() {
-        UndefinedFunctionException e = new UndefinedFunctionException(Nil.getInstance());
+        UndefinedFunctionException e = new UndefinedFunctionException(NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);
@@ -89,7 +90,7 @@ public class EVALTester {
 
     @Test
     public void undefinedSymbolException_HasMessageText() {
-        UndefinedSymbolException e = new UndefinedSymbolException(Nil.getInstance());
+        UndefinedSymbolException e = new UndefinedSymbolException(NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);

test/function/builtin/EXITTester.java

@@ -41,7 +41,7 @@ public class EXITTester {
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testExitWithTooManyArguments() {
+    public void exitWithTooManyArguments() {
         evaluateString("(exit 1)");
     }
 

test/function/builtin/FUNCALLTester.java

@@ -20,14 +20,14 @@ public class FUNCALLTester {
     }
 
     @Test
-    public void testFuncallWithNumbers() {
+    public void funcallWithNumbers() {
         String input = "(funcall '+ 1 2 3)";
 
         assertSExpressionsMatch(parseString("6"), evaluateString(input));
     }
 
     @Test
-    public void testFuncallWithUserDefinedFunction() {
+    public void funcallWithUserDefinedFunction() {
         String defineUserFunction = "(defun x (n m) (+ n m))";
         String input = "(funcall 'x 2 30)";
 
@@ -36,7 +36,7 @@ public class FUNCALLTester {
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testFuncallWithTooFewArguments() {
+    public void funcallWithTooFewArguments() {
         evaluateString("(funcall)");
     }
 

test/function/builtin/LOADTester.java

@@ -75,17 +75,17 @@ public class LOADTester {
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testLoadWithBadArgumentType() {
+    public void loadWithBadArgumentType() {
         evaluateString("(load '1)");
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testLoadWithTooManyArguments() {
+    public void loadWithTooManyArguments() {
         evaluateString("(load \"1\" \"2\")");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testLoadWithTooFewArguments() {
+    public void loadWithTooFewArguments() {
         evaluateString("(load)");
     }
 

test/function/builtin/PRINTTester.java

@@ -42,12 +42,12 @@ public class PRINTTester {
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testPrintWithTooManyArguments() {
+    public void printWithTooManyArguments() {
         evaluateString("(print '1 '2)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testPrintWithTooFewArguments() {
+    public void printWithTooFewArguments() {
         evaluateString("(print)");
     }
 

test/function/builtin/SETTester.java

@@ -29,7 +29,7 @@ public class SETTester {
     }
 
     @Test
-    public void testSet() {
+    public void set() {
         evaluateString("(set 'a 23)");
         assertSExpressionsMatch(new LispNumber("23"), evaluateString("a"));
     }
@@ -80,17 +80,17 @@ public class SETTester {
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testSetWithNonSymbol() {
+    public void setWithNonSymbol() {
         evaluateString("(set '1 2)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testSetWithTooFewArguments() {
+    public void setWithTooFewArguments() {
         evaluateString("(set 'x)");
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testSetWithTooManyArguments() {
+    public void setWithTooManyArguments() {
         evaluateString("(set 'a 'b 'c)");
     }
 

test/function/builtin/SYMBOL_FUNCTIONTester.java

@@ -1,13 +1,13 @@
 package function.builtin;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
 import static testutil.TestUtilities.evaluateString;
 
 import org.junit.*;
 
 import function.ArgumentValidator.*;
 import function.builtin.SYMBOL_FUNCTION.UndefinedSymbolFunctionException;
-import sexpression.Nil;
 import table.FunctionTable;
 
 public class SYMBOL_FUNCTIONTester {
@@ -23,21 +23,21 @@ public class SYMBOL_FUNCTIONTester {
     }
 
     @Test
-    public void testSymbolFunction_BuiltInFunction() {
+    public void symbolFunction_BuiltInFunction() {
         String input = "(symbol-function '+)";
 
         assertEquals("#<FUNCTION +>", evaluateString(input).toString());
     }
 
     @Test
-    public void testSymbolFunction_BuiltInSpecialFunction() {
+    public void symbolFunction_BuiltInSpecialFunction() {
         String input = "(symbol-function 'if)";
 
         assertEquals("#<SPECIAL-FUNCTION IF>", evaluateString(input).toString());
     }
 
     @Test
-    public void testSymbolFunction_UserDefinedFunction() {
+    public void symbolFunction_UserDefinedFunction() {
         String defineUserFunction = "(defun y (n m) (+ n m))";
         String input = "(symbol-function 'y)";
 
@@ -46,30 +46,30 @@ public class SYMBOL_FUNCTIONTester {
     }
 
     @Test(expected = UndefinedSymbolFunctionException.class)
-    public void testSymbolFunction_NonFunction() {
+    public void symbolFunction_NonFunction() {
         String input = "(symbol-function 'a)";
 
         evaluateString(input);
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testSymbolFunctionWithBadArgumentType() {
+    public void symbolFunctionWithBadArgumentType() {
         evaluateString("(symbol-function 2)");
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testSymbolFunctionWithTooManyArguments() {
+    public void symbolFunctionWithTooManyArguments() {
         evaluateString("(symbol-function 'a 'b)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testSymbolFunctionWithTooFewArguments() {
+    public void symbolFunctionWithTooFewArguments() {
         evaluateString("(symbol-function)");
     }
 
     @Test
     public void undefinedSymbolFunctionException_HasMessageText() {
-        UndefinedSymbolFunctionException e = new UndefinedSymbolFunctionException(Nil.getInstance());
+        UndefinedSymbolFunctionException e = new UndefinedSymbolFunctionException(NIL);
 
         assertNotNull(e.getMessage());
         assertTrue(e.getMessage().length() > 0);

test/function/builtin/cons/CONSTester.java

@@ -10,49 +10,49 @@ import sexpression.*;
 public class CONSTester {
 
     @Test
-    public void testConsWithNilValues() {
+    public void consWithNilValues() {
         String input = "(cons () nil)";
 
         assertSExpressionsMatch(parseString("(())"), evaluateString(input));
     }
 
     @Test
-    public void testConsWithTwoSymbols() {
+    public void consWithTwoSymbols() {
         String input = "(cons 'a 'b)";
 
         assertSExpressionsMatch(new Cons(new Symbol("A"), new Symbol("B")), evaluateString(input));
     }
 
     @Test
-    public void testConsWithListAsRest() {
+    public void consWithListAsRest() {
         String input = "(cons 1 '(2 3))";
 
         assertSExpressionsMatch(parseString("(1 2 3)"), evaluateString(input));
     }
 
     @Test
-    public void testConsWithTwoLists() {
+    public void consWithTwoLists() {
         String input = "(cons '(1 2) '(3 4))";
 
         assertSExpressionsMatch(parseString("((1 2) 3 4)"), evaluateString(input));
     }
 
     @Test
-    public void testConsWithList() {
+    public void consWithList() {
         String input = "(cons nil '(2 3))";
 
         assertSExpressionsMatch(parseString("(nil 2 3)"), evaluateString(input));
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testConsWithTooManyArguments() {
+    public void consWithTooManyArguments() {
         String input = "(cons 1 2 3)";
 
         evaluateString(input);
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testConsWithTooFewArguments() {
+    public void consWithTooFewArguments() {
         String input = "(cons 1)";
 
         evaluateString(input);

test/function/builtin/cons/LENGTHTester.java

@@ -9,38 +9,38 @@ import function.ArgumentValidator.*;
 public class LENGTHTester {
 
     @Test
-    public void testLengthOfNil() {
+    public void lengthOfNil() {
         String input = "(length '())";
 
         assertSExpressionsMatch(parseString("0"), evaluateString(input));
     }
 
     @Test
-    public void testLengthOfListOfOneElement() {
+    public void lengthOfListOfOneElement() {
         String input = "(length '(1))";
 
         assertSExpressionsMatch(parseString("1"), evaluateString(input));
     }
 
     @Test
-    public void testLengthOfListOfManyElements() {
+    public void lengthOfListOfManyElements() {
         String input = "(length '(1 2 3 4 5))";
 
         assertSExpressionsMatch(parseString("5"), evaluateString(input));
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testLengthWithNonList() {
+    public void lengthWithNonList() {
         evaluateString("(length 'x)");
     }
 
     @Test(expected = TooManyArgumentsException.class)
-    public void testLengthWithTooManyArguments() {
+    public void lengthWithTooManyArguments() {
         evaluateString("(length '(1 2) '(1 2))");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testLengthWithTooFewArguments() {
+    public void lengthWithTooFewArguments() {
         evaluateString("(length)");
     }
 

test/function/builtin/cons/LISTTester.java

@@ -1,5 +1,6 @@
 package function.builtin.cons;
 
+import static function.builtin.cons.LIST.makeList;
 import static testutil.TestUtilities.*;
 
 import org.junit.Test;
@@ -7,50 +8,50 @@ import org.junit.Test;
 public class LISTTester {
 
     @Test
-    public void testListWithNoArguments() {
+    public void listWithNoArguments() {
         String input = "(list)";
 
         assertSExpressionsMatch(parseString("nil"), evaluateString(input));
     }
 
     @Test
-    public void testListWithOneArgument() {
+    public void listWithOneArgument() {
         String input = "(list 1)";
 
         assertSExpressionsMatch(parseString("(1)"), evaluateString(input));
     }
 
     @Test
-    public void testListWithTwoArguments() {
+    public void listWithTwoArguments() {
         String input = "(list 2 3)";
 
         assertSExpressionsMatch(parseString("(2 3)"), evaluateString(input));
     }
 
     @Test
-    public void testListWithManyArguments() {
+    public void listWithManyArguments() {
         String input = "(list 'm 'a 'n 'y 'a 'r 'g 's)";
 
         assertSExpressionsMatch(parseString("(m a n y a r g s)"), evaluateString(input));
     }
 
     @Test
-    public void testListWithOneListArgument() {
+    public void listWithOneListArgument() {
         String input = "(list '(1))";
 
         assertSExpressionsMatch(parseString("((1))"), evaluateString(input));
     }
 
     @Test
-    public void testListWithManyListArguments() {
+    public void listWithManyListArguments() {
         String input = "(list '(1) '(2 3) ())";
 
         assertSExpressionsMatch(parseString("((1) (2 3) ())"), evaluateString(input));
     }
 
     @Test
-    public void testMakeList() {
+    public void staticMakeList() {
-        assertSExpressionsMatch(parseString("(22)"), LIST.makeList(parseString("22")));
+        assertSExpressionsMatch(parseString("(22)"), makeList(parseString("22")));
     }
 
 }

test/function/builtin/math/DIVIDETester.java

@@ -9,54 +9,54 @@ import function.ArgumentValidator.*;
 public class DIVIDETester {
 
     @Test
-    public void testDivideWithOne() {
+    public void divideWithOne() {
         String input = "(/ 1)";
 
         assertSExpressionsMatch(parseString("1"), evaluateString(input));
     }
 
     @Test
-    public void testDivideWithTwo() {
+    public void divideWithTwo() {
         String input = "(/ 2)";
 
         assertSExpressionsMatch(parseString("0"), evaluateString(input));
     }
 
     @Test
-    public void testDivideTwoNumbers() {
+    public void divideTwoNumbers() {
         String input = "(/ 24 3)";
 
         assertSExpressionsMatch(parseString("8"), evaluateString(input));
     }
 
     @Test
-    public void testDivideSeveralNumbers() {
+    public void divideSeveralNumbers() {
         String input = "(/ 256 2 2 8)";
 
         assertSExpressionsMatch(parseString("8"), evaluateString(input));
     }
 
     @Test
-    public void testDivideTwoNumbersWithRemainder() {
+    public void divideTwoNumbersWithRemainder() {
         String input = "(/ 9 2)";
 
         assertSExpressionsMatch(parseString("4"), evaluateString(input));
     }
 
     @Test
-    public void testDivideSeveralNumbersWithRemainder() {
+    public void divideSeveralNumbersWithRemainder() {
         String input = "(/ 19 2 5)";
 
         assertSExpressionsMatch(parseString("1"), evaluateString(input));
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testDivideWithNonNumber() {
+    public void divideWithNonNumber() {
         evaluateString("(/ 'x)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testDivideWithTooFewArguments() {
+    public void divideWithTooFewArguments() {
         evaluateString("(/)");
     }
 

test/function/builtin/math/MINUSTester.java

@@ -10,40 +10,40 @@ import sexpression.LispNumber;
 public class MINUSTester {
 
     @Test
-    public void testMinusWithOneNumber() {
+    public void minusWithOneNumber() {
         String input = "(- 27)";
 
         assertSExpressionsMatch(new LispNumber("-27"), evaluateString(input));
     }
 
     @Test
-    public void testMinusWithTwoNumbers() {
+    public void minusWithTwoNumbers() {
         String input = "(- 5 3)";
 
         assertSExpressionsMatch(new LispNumber("2"), evaluateString(input));
     }
 
     @Test
-    public void testMinusWithManyNumbers_PositiveResult() {
+    public void minusWithManyNumbers_PositiveResult() {
         String input = "(- 200 100 10 5)";
 
         assertSExpressionsMatch(new LispNumber("85"), evaluateString(input));
     }
 
     @Test
-    public void testMinusWithManyNumbers_NegativeResult() {
+    public void minusWithManyNumbers_NegativeResult() {
         String input = "(- 100 200 20 5)";
 
         assertSExpressionsMatch(new LispNumber("-125"), evaluateString(input));
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testMinusWithNonNumber() {
+    public void minusWithNonNumber() {
         evaluateString("(- 'a 'b)");
     }
 
     @Test(expected = TooFewArgumentsException.class)
-    public void testMinusWithTooFewArguments() {
+    public void minusWithTooFewArguments() {
         evaluateString("(-)");
     }
 

test/function/builtin/math/MULTIPLYTester.java

@@ -10,42 +10,42 @@ import sexpression.LispNumber;
 public class MULTIPLYTester {
 
     @Test
-    public void testMultiplyWithNoArguments() {
+    public void multiplyWithNoArguments() {
         String input = "(*)";
 
         assertSExpressionsMatch(new LispNumber("1"), evaluateString(input));
     }
 
     @Test
-    public void testMultiplyWithOneNumber() {
+    public void multiplyWithOneNumber() {
         String input = "(* 8)";
 
         assertSExpressionsMatch(new LispNumber("8"), evaluateString(input));
     }
 
     @Test
-    public void testMultiplyWithTwoNumbers() {
+    public void multiplyWithTwoNumbers() {
         String input = "(* 5 3)";
 
         assertSExpressionsMatch(new LispNumber("15"), evaluateString(input));
     }
 
     @Test
-    public void testMultiplyWithManyNumbers_PositiveResult() {
+    public void multiplyWithManyNumbers_PositiveResult() {
         String input = "(* 2 3 5 1)";
 
         assertSExpressionsMatch(new LispNumber("30"), evaluateString(input));
     }
 
     @Test
-    public void testMultiplyWithManyNumbers_NegativeResult() {
+    public void multiplyWithManyNumbers_NegativeResult() {
         String input = "(* 3 (- 2) 10 2)";
 
         assertSExpressionsMatch(new LispNumber("-120"), evaluateString(input));
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testMultiplyWithNonNumber() {
+    public void multiplyWithNonNumber() {
         evaluateString("(* 'a 'b)");
     }
 

test/function/builtin/math/PLUSTester.java

@@ -10,42 +10,42 @@ import sexpression.LispNumber;
 public class PLUSTester {
 
     @Test
-    public void testPlusWithNoArguments() {
+    public void plusWithNoArguments() {
         String input = "(+)";
 
         assertSExpressionsMatch(new LispNumber("0"), evaluateString(input));
     }
 
     @Test
-    public void testPlusWithOneNumber() {
+    public void plusWithOneNumber() {
         String input = "(+ 27)";
 
         assertSExpressionsMatch(new LispNumber("27"), evaluateString(input));
     }
 
     @Test
-    public void testPlusWithTwoNumbers() {
+    public void plusWithTwoNumbers() {
         String input = "(+ 5 3)";
 
         assertSExpressionsMatch(new LispNumber("8"), evaluateString(input));
     }
 
     @Test
-    public void testPlusWithManyNumbers_PositiveResult() {
+    public void plusWithManyNumbers_PositiveResult() {
         String input = "(+ 200 100 10 5)";
 
         assertSExpressionsMatch(new LispNumber("315"), evaluateString(input));
     }
 
     @Test
-    public void testPlusWithManyNumbers_NegativeResult() {
+    public void plusWithManyNumbers_NegativeResult() {
         String input = "(+ 100 (- 200) 20 5)";
 
         assertSExpressionsMatch(new LispNumber("-75"), evaluateString(input));
     }
 
     @Test(expected = BadArgumentTypeException.class)
-    public void testPlusWithNonNumber() {
+    public void plusWithNonNumber() {
         evaluateString("(+ 'a 'b)");
     }
 

test/function/builtin/special/LAMBDATester.java

@@ -1,6 +1,9 @@
 package function.builtin.special;
 
 import static org.junit.Assert.*;
+import static sexpression.LispNumber.ONE;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 import static testutil.TestUtilities.*;
 
 import org.junit.Test;
@@ -26,21 +29,19 @@ public class LAMBDATester {
 
     @Test
     public void lambdaExpressionIsLambdaExpression() {
-        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"),
+        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), new Cons(NIL, new Cons(NIL, NIL)));
-                                         new Cons(Nil.getInstance(), new Cons(Nil.getInstance(), Nil.getInstance())));
 
         assertTrue(LAMBDA.isLambdaExpression(lambdaExpression));
     }
 
     @Test
     public void somethingElseIsNotLambdaExpression() {
-        assertFalse(LAMBDA.isLambdaExpression(Symbol.T));
+        assertFalse(LAMBDA.isLambdaExpression(T));
     }
 
     @Test
     public void createLambdaExpression() {
-        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"),
+        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), new Cons(NIL, new Cons(NIL, NIL)));
-                                         new Cons(Nil.getInstance(), new Cons(Nil.getInstance(), Nil.getInstance())));
 
         assertSExpressionsMatch(parseString("(:LAMBDA () ())"),
                                 LAMBDA.createFunction(lambdaExpression).getLambdaExpression());
@@ -62,14 +63,14 @@ public class LAMBDATester {
 
     @Test(expected = DottedArgumentListException.class)
     public void createFunctionWithDottedArgumentList() {
-        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), new Cons(Nil.getInstance(), LispNumber.ONE));
+        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), new Cons(NIL, ONE));
 
         LAMBDA.createFunction(lambdaExpression);
     }
 
     @Test(expected = BadArgumentTypeException.class)
     public void createFunctionWithNonList() {
-        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), LispNumber.ONE);
+        Cons lambdaExpression = new Cons(new Symbol("LAMBDA"), ONE);
 
         LAMBDA.createFunction(lambdaExpression);
     }

test/function/builtin/special/LETTester.java

@@ -1,12 +1,13 @@
 package function.builtin.special;
 
+import static sexpression.Nil.NIL;
 import static testutil.TestUtilities.*;
 
 import org.junit.*;
 
 import function.ArgumentValidator.*;
 import function.builtin.EVAL.UndefinedSymbolException;
-import sexpression.*;
+import sexpression.LispNumber;
 import table.ExecutionContext;
 
 public class LETTester {
@@ -38,7 +39,7 @@ public class LETTester {
     public void emptyLet_ReturnsNil() {
         String input = "(let ())";
 
-        assertSExpressionsMatch(Nil.getInstance(), evaluateString(input));
+        assertSExpressionsMatch(NIL, evaluateString(input));
     }
 
     @Test

test/parser/LispParserTester.java

@@ -29,7 +29,7 @@ public class LispParserTester {
     }
 
     @Test
-    public void testEofMethod_ReturnsTrueWithNoInput() {
+    public void eofMethod_ReturnsTrueWithNoInput() {
         String input = "";
         LispParser parser = createLispParser(input);
 
@@ -37,7 +37,7 @@ public class LispParserTester {
     }
 
     @Test
-    public void testEofMethod_ReturnsFalseWithSomeInput() {
+    public void eofMethod_ReturnsFalseWithSomeInput() {
         String input = "abc";
         LispParser parser = createLispParser(input);
 
@@ -45,7 +45,7 @@ public class LispParserTester {
     }
 
     @Test
-    public void testEofMethod_ReturnsTrueAfterSomeInput() {
+    public void eofMethod_ReturnsTrueAfterSomeInput() {
         String input = "(yyz 9 9 9)";
         LispParser parser = createLispParser(input);
 
@@ -54,7 +54,7 @@ public class LispParserTester {
     }
 
     @Test
-    public void testEofMethod_ReturnsFalseAfterMultipleExpressions() {
+    public void eofMethod_ReturnsFalseAfterMultipleExpressions() {
         String input = "()()()";
         LispParser parser = createLispParser(input);
 
@@ -66,7 +66,7 @@ public class LispParserTester {
     }
 
     @Test
-    public void testEofMethod_ReturnsTrueAfterMultipleExpressions() {
+    public void eofMethod_ReturnsTrueAfterMultipleExpressions() {
         String input = "()()()";
         LispParser parser = createLispParser(input);
 

test/sexpression/SExpressionTester.java

@@ -2,6 +2,7 @@ package sexpression;
 
 import static error.ErrorManager.Severity.ERROR;
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
 
 import java.math.BigInteger;
 
@@ -20,59 +21,59 @@ public class SExpressionTester {
     public void setUp() throws Exception {}
 
     @Test
-    public void testNilToString() {
+    public void nilToString() {
         String input = "NIL";
 
-        assertSExpressionMatchesString(input, Nil.getInstance());
+        assertSExpressionMatchesString(input, NIL);
     }
 
     @Test
-    public void testNumberToString() {
+    public void numberToString() {
         String input = "12";
 
         assertSExpressionMatchesString(input, new LispNumber(input));
     }
 
     @Test
-    public void testNumberValueToString() {
+    public void numberValueToString() {
         String expected = "12";
 
         assertSExpressionMatchesString(expected, new LispNumber("12"));
     }
 
     @Test
-    public void testStringToString() {
+    public void stringToString() {
         String input = "\"hi\"";
 
         assertSExpressionMatchesString(input, new LispString(input));
     }
 
     @Test
-    public void testSymbolToString() {
+    public void symbolToString() {
         String input = "symbol";
 
         assertSExpressionMatchesString(input.toUpperCase(), new Symbol(input));
     }
 
     @Test
-    public void testSimpleConsToString() {
+    public void simpleConsToString() {
         String expected = "(1)";
-        Cons cons = new Cons(new LispNumber("1"), Nil.getInstance());
+        Cons cons = new Cons(new LispNumber("1"), NIL);
 
         assertSExpressionMatchesString(expected, cons);
     }
 
     @Test
-    public void testComplexConsToString() {
+    public void complexConsToString() {
         String expected = "(1 A \"string\")";
         Cons list = new Cons(new LispNumber("1"),
-                             new Cons(new Symbol("a"), new Cons(new LispString("\"string\""), Nil.getInstance())));
+                             new Cons(new Symbol("a"), new Cons(new LispString("\"string\""), NIL)));
 
         assertSExpressionMatchesString(expected, list);
     }
 
     @Test
-    public void testImproperListToString() {
+    public void improperListToString() {
         String expected = "(A . B)";
         Cons list = new Cons(new Symbol("A"), new Symbol("B"));
 
@@ -80,58 +81,58 @@ public class SExpressionTester {
     }
 
     @Test
-    public void testLambdaExpressionToString() {
+    public void lambdaExpressionToString() {
         String expected = "(LAMBDA)";
-        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), Nil.getInstance()), null);
+        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), NIL), null);
 
         assertSExpressionMatchesString(expected, lambda);
     }
 
     @Test
-    public void testLambdaExpressionGetLambdaExpression() {
+    public void lambdaExpressionGetLambdaExpression() {
         String expected = "(LAMBDA)";
-        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), Nil.getInstance()), null);
+        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), NIL), null);
 
         assertSExpressionMatchesString(expected, lambda.getLambdaExpression());
     }
 
     @Test
-    public void testLambdaExpressionGetFunction() {
+    public void lambdaExpressionGetFunction() {
         String expected = "(LAMBDA)";
-        UserDefinedFunction function = new UserDefinedFunction(expected, Nil.getInstance(), Nil.getInstance());
+        UserDefinedFunction function = new UserDefinedFunction(expected, NIL, NIL);
-        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), Nil.getInstance()), function);
+        LambdaExpression lambda = new LambdaExpression(new Cons(new Symbol("lambda"), NIL), function);
 
         assertEquals(function, lambda.getFunction());
     }
 
     @Test
-    public void testFirstOfNilIsNil() {
+    public void firstOfNilIsNil() {
-        assertEquals(Nil.getInstance(), Nil.getInstance().getFirst());
+        assertEquals(NIL, NIL.getFirst());
     }
 
     @Test
-    public void testRestOfNilIsNil() {
+    public void restOfNilIsNil() {
-        assertEquals(Nil.getInstance(), Nil.getInstance().getRest());
+        assertEquals(NIL, NIL.getRest());
     }
 
     @Test
     public void afterSettingFirstOfNil_ShouldStillBeNil() {
-        Cons nil = Nil.getInstance();
+        Cons nil = NIL;
         nil.setFirst(new LispNumber("2"));
 
-        assertEquals(Nil.getInstance(), nil.getFirst());
+        assertEquals(NIL, nil.getFirst());
     }
 
     @Test
     public void afterSettingRestOfNil_ShouldStillBeNil() {
-        Cons nil = Nil.getInstance();
+        Cons nil = NIL;
         nil.setRest(new LispNumber("2"));
 
-        assertEquals(Nil.getInstance(), nil.getRest());
+        assertEquals(NIL, nil.getRest());
     }
 
     @Test
-    public void testNumberValue() {
+    public void numberValue() {
         BigInteger value = new BigInteger("12");
         LispNumber number = new LispNumber(value.toString());
 
@@ -139,12 +140,12 @@ public class SExpressionTester {
     }
 
     @Test(expected = InvalidNumberException.class)
-    public void testInvalidNumberText_ThrowsException() {
+    public void invalidNumberText_ThrowsException() {
         new LispNumber("a");
     }
 
     @Test
-    public void testInvalidNumberException_HasCorrectSeverity() {
+    public void invalidNumberException_HasCorrectSeverity() {
         try {
             new LispNumber("a");
         } catch (InvalidNumberException e) {
@@ -153,7 +154,7 @@ public class SExpressionTester {
     }
 
     @Test
-    public void testInvalidNumberException_HasMessageText() {
+    public void invalidNumberException_HasMessageText() {
         try {
             new LispNumber("a");
         } catch (InvalidNumberException e) {
@@ -165,7 +166,7 @@ public class SExpressionTester {
     }
 
     @Test
-    public void testLispNumberConstants() {
+    public void lispNumberConstants() {
         assertEquals(BigInteger.ZERO, LispNumber.ZERO.getValue());
         assertEquals(BigInteger.ONE, LispNumber.ONE.getValue());
     }

test/table/ExecutionContextTester.java

@@ -1,11 +1,11 @@
 package table;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import org.junit.*;
 
-import sexpression.*;
-
 public class ExecutionContextTester {
 
     private ExecutionContext executionContext;
@@ -45,40 +45,40 @@ public class ExecutionContextTester {
 
     @Test
     public void lookupVariable() {
-        executionContext.getScope().put("test", Symbol.T);
+        executionContext.getScope().put("test", T);
 
-        assertEquals(Symbol.T, executionContext.lookupSymbolValue("test"));
+        assertEquals(T, executionContext.lookupSymbolValue("test"));
     }
 
     @Test
     public void lookupLocalVariable() {
         SymbolTable scope = new SymbolTable(executionContext.getScope());
 
-        scope.put("local", Symbol.T);
+        scope.put("local", T);
         executionContext.setScope(scope);
 
-        assertEquals(Symbol.T, executionContext.lookupSymbolValue("local"));
+        assertEquals(T, executionContext.lookupSymbolValue("local"));
     }
 
     @Test
     public void lookupGlobalVariable() {
         SymbolTable scope = new SymbolTable(executionContext.getScope());
 
-        executionContext.getScope().put("global", Symbol.T);
+        executionContext.getScope().put("global", T);
         executionContext.setScope(scope);
 
-        assertEquals(Symbol.T, executionContext.lookupSymbolValue("global"));
+        assertEquals(T, executionContext.lookupSymbolValue("global"));
     }
 
     @Test
     public void lookupShadowedVariable() {
         SymbolTable scope = new SymbolTable(executionContext.getScope());
 
-        scope.put("shadowed", Nil.getInstance());
+        scope.put("shadowed", NIL);
-        executionContext.getScope().put("shadowed", Symbol.T);
+        executionContext.getScope().put("shadowed", T);
         executionContext.setScope(scope);
 
-        assertEquals(Nil.getInstance(), executionContext.lookupSymbolValue("shadowed"));
+        assertEquals(NIL, executionContext.lookupSymbolValue("shadowed"));
     }
 
 }

test/table/FunctionTableTester.java

@@ -1,6 +1,8 @@
 package table;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import java.util.*;
 
@@ -18,7 +20,7 @@ public class FunctionTableTester {
 
         @Override
         public SExpression call(Cons argList) {
-            return Nil.getInstance();
+            return NIL;
         }
     }
 
@@ -31,15 +33,15 @@ public class FunctionTableTester {
 
         @Override
         public SExpression call(Cons argList) {
-            return Nil.getInstance();
+            return NIL;
         }
     }
 
-    public static class NamelessFunction extends LispFunction {
+    public static class UglyFunction extends LispFunction {
 
         @Override
         public SExpression call(Cons argList) {
-            return Nil.getInstance();
+            return NIL;
         }
     }
 
@@ -48,7 +50,7 @@ public class FunctionTableTester {
 
             @Override
             public SExpression call(Cons argList) {
-                return Symbol.T;
+                return T;
             }
         };
     }
@@ -140,12 +142,12 @@ public class FunctionTableTester {
     @Test
     public void namelessBuiltIn_DoesNotCauseNPE() {
         Set<Class<? extends LispFunction>> namelessBuiltins = new HashSet<>();
-        namelessBuiltins.add(NamelessFunction.class);
+        namelessBuiltins.add(UglyFunction.class);
 
         FunctionTable.reset(namelessBuiltins);
 
-        assertFalse(FunctionTable.isAlreadyDefined("NAMELESS"));
+        assertFalse(FunctionTable.isAlreadyDefined("UGLY"));
-        assertNull(FunctionTable.lookupFunction("NAMELESS"));
+        assertNull(FunctionTable.lookupFunction("UGLY"));
     }
 
 }

test/table/SymbolTableTester.java

@@ -1,11 +1,11 @@
 package table;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
 import org.junit.*;
 
-import sexpression.*;
-
 public class SymbolTableTester {
 
     private SymbolTable symbolTable;
@@ -22,24 +22,24 @@ public class SymbolTableTester {
 
     @Test
     public void lookupSymbolInTable() {
-        symbolTable.put("symbol", Symbol.T);
+        symbolTable.put("symbol", T);
 
         assertTrue(symbolTable.contains("symbol"));
     }
 
     @Test
     public void retrieveSymbolValue() {
-        symbolTable.put("symbol", Symbol.T);
+        symbolTable.put("symbol", T);
 
-        assertEquals(Symbol.T, symbolTable.get("symbol"));
+        assertEquals(T, symbolTable.get("symbol"));
     }
 
     @Test
     public void redefineSymbolValue() {
-        symbolTable.put("symbol", Symbol.T);
+        symbolTable.put("symbol", T);
-        symbolTable.put("symbol", Nil.getInstance());
+        symbolTable.put("symbol", NIL);
 
-        assertEquals(Nil.getInstance(), symbolTable.get("symbol"));
+        assertEquals(NIL, symbolTable.get("symbol"));
     }
 
     @Test
@@ -51,11 +51,11 @@ public class SymbolTableTester {
 
     @Test
     public void lookupSymbolInParentTable() {
-        symbolTable.put("symbol", Symbol.T);
+        symbolTable.put("symbol", T);
         SymbolTable childTable = new SymbolTable(symbolTable);
         SymbolTable parentTable = childTable.getParent();
 
-        assertEquals(Symbol.T, parentTable.get("symbol"));
+        assertEquals(T, parentTable.get("symbol"));
     }
 
 }

test/testutil/TypeAssertions.java

@@ -1,8 +1,10 @@
 package testutil;
 
 import static org.junit.Assert.*;
+import static sexpression.Nil.NIL;
+import static sexpression.Symbol.T;
 
-import sexpression.*;
+import sexpression.SExpression;
 
 public final class TypeAssertions {
 
@@ -18,7 +20,7 @@ public final class TypeAssertions {
     }
 
     public static void assertNil(SExpression sExpression) {
-        assertEquals(Nil.getInstance(), sExpression);
+        assertEquals(NIL, sExpression);
 
         assertTrue(sExpression.isAtom());
         assertFalse(sExpression.isCons());
@@ -65,7 +67,7 @@ public final class TypeAssertions {
     }
 
     public static void assertT(SExpression sExpression) {
-        assertEquals(Symbol.T, sExpression);
+        assertEquals(T, sExpression);
     }
 
 }

test/token/TokenFactoryTester.java

@@ -26,65 +26,65 @@ public class TokenFactoryTester {
     }
 
     @Test
-    public void testEofTokenCreation() {
+    public void eofTokenCreation() {
         assertTrue(tokenFactory.createEofToken(testPosition) instanceof Eof);
     }
 
     @Test
-    public void testLeftParenthesisCreation() {
+    public void leftParenthesisCreation() {
         String text = "(";
         assertTrue(createToken(text) instanceof LeftParenthesis);
     }
 
     @Test
-    public void testRightParenthesisCreation() {
+    public void rightParenthesisCreation() {
         String text = ")";
         assertTrue(createToken(text) instanceof RightParenthesis);
     }
 
     @Test
-    public void testQuoteMarkCreation() {
+    public void quoteMarkCreation() {
         String text = "'";
         assertTrue(createToken(text) instanceof QuoteMark);
     }
 
     @Test
-    public void testNumberCreation() {
+    public void numberCreation() {
         String text = "987";
         assertTrue(createToken(text) instanceof Number);
     }
 
     @Test
-    public void testPrefixedNumberCreation() {
+    public void prefixedNumberCreation() {
         String text = "-987";
         assertTrue(createToken(text) instanceof Number);
     }
 
     @Test
-    public void testIdentifierCreation() {
+    public void identifierCreation() {
         String text = "identifier";
         assertTrue(createToken(text) instanceof Identifier);
     }
 
     @Test
-    public void testPrefixedIdentifierCreation() {
+    public void prefixedIdentifierCreation() {
         String text = "-identifier";
         assertTrue(createToken(text) instanceof Identifier);
     }
 
     @Test
-    public void testStringCreation() {
+    public void stringCreation() {
         String text = "\"string\"";
         assertTrue(createToken(text) instanceof QuotedString);
     }
 
     @Test(expected = EmptyTokenTextException.class)
-    public void testEmptyString_ThrowsException() {
+    public void emptyString_ThrowsException() {
         createToken("");
     }
 
     @Test
-    public void EmptyTokenTextException_ContainsCorrectSeverity() {
+    public void emptyTokenTextException_ContainsCorrectSeverity() {
         try {
             createToken("");
         } catch (EmptyTokenTextException e) {
@@ -93,7 +93,7 @@ public class TokenFactoryTester {
     }
 
     @Test
-    public void EmptyTokenTextException_ContainsMessage() {
+    public void emptyTokenTextException_ContainsMessage() {
         try {
             createToken("");
         } catch (EmptyTokenTextException e) {
@@ -104,7 +104,7 @@ public class TokenFactoryTester {
     }
 
     @Test(expected = BadCharacterException.class)
-    public void testBadCharacter_ThrowsException() {
+    public void badCharacter_ThrowsException() {
         createToken("[abc]");
     }
 

test/util/CharactersTester.java

@@ -9,7 +9,7 @@ import org.junit.Test;
 public class CharactersTester {
 
     @Test
-    public void testConstructorIsPrivate() throws Exception {
+    public void constructorIsPrivate() throws Exception {
         Constructor<Characters> constructor = Characters.class.getDeclaredConstructor();
 
         assertTrue(Modifier.isPrivate(constructor.getModifiers()));