Added unit tests and refactored the code for the list function

src/function/builtin/LIST.java

@@ -1,35 +1,34 @@
 package function.builtin;
 
-import function.LispFunction;
+import function.*;
 import sexpression.*;
 
-/**
- * <code>LIST</code> represents the LIST function in Lisp.
- */
 public class LIST extends LispFunction {
 
-    /**
-     * Places the given S-expression into a list.
-     *
-     * @param sexpr
-     *  the S-expression to be placed into a list
-     * @return
-     *  a list with <code>sexpr</code> as the car and NIL as the cdr.
-     */
+    private ArgumentValidator argumentValidator;
+
+    public LIST() {
+        this.argumentValidator = new ArgumentValidator("LIST");
+    }
+
     public static Cons makeList(SExpression sexpr) {
         return new Cons(sexpr, Nil.getInstance());
     }
 
-    public Cons call(Cons argList) {
-        if (argList.nullp()) {
-            // return NIL if there were no arguments passed to LIST
-            return Nil.getInstance();
+    public Cons call(Cons argumentList) {
+        argumentValidator.validate(argumentList);
+
+        return callRecursive(argumentList);
     }
 
-        SExpression argCar = argList.getCar();
-        Cons argCdr = (Cons) argList.getCdr();
+    private Cons callRecursive(Cons argumentList) {
+        if (argumentList.nullp())
+            return Nil.getInstance();
 
-        return new Cons(argCar, call(argCdr));
+        SExpression firstArgument = argumentList.getCar();
+        Cons remainingArguments = (Cons) argumentList.getCdr();
+
+        return new Cons(firstArgument, callRecursive(remainingArguments));
     }
 
 }

test/function/builtin/LISTTester.java

@@ -0,0 +1,56 @@
+package function.builtin;
+
+import static testutil.TestUtilities.*;
+
+import org.junit.Test;
+
+public class LISTTester {
+
+    @Test
+    public void testListWithNoArguments() {
+        String input = "(list)";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("nil"));
+    }
+
+    @Test
+    public void testListWithOneArgument() {
+        String input = "(list 1)";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("(1)"));
+    }
+
+    @Test
+    public void testListWithTwoArguments() {
+        String input = "(list 2 3)";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("(2 3)"));
+    }
+
+    @Test
+    public void testListWithManyArguments() {
+        String input = "(list 'm 'a 'n 'y 'a 'r 'g 's)";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("(m a n y a r g s)"));
+    }
+
+    @Test
+    public void testListWithOneListArgument() {
+        String input = "(list '(1))";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("((1))"));
+    }
+
+    @Test
+    public void testListWithManyListArguments() {
+        String input = "(list '(1) '(2 3) ())";
+
+        assertSExpressionsMatch(evaluateString(input), parseString("((1) (2 3) ())"));
+    }
+
+    @Test
+    public void testMakeList() {
+        assertSExpressionsMatch(LIST.makeList(parseString("22")), parseString("(22)"));
+    }
+
+}