diff --git a/src/function/builtin/SYMBOL_FUNCTION.java b/src/function/builtin/SYMBOL_FUNCTION.java
index e4eac3a..42c310b 100644
--- a/src/function/builtin/SYMBOL_FUNCTION.java
+++ b/src/function/builtin/SYMBOL_FUNCTION.java
@@ -1,61 +1,50 @@
 package function.builtin;
 
+import java.text.MessageFormat;
+
+import error.LispException;
 import function.*;
-import function.builtin.cons.LENGTH;
 import sexpression.*;
 
-/**
- * <code>SYMBOL_FUNCTION</code> represents the SYMBOL-FUNCTION function in 
- * Lisp.
- */
 public class SYMBOL_FUNCTION extends LispFunction {
 
-    // The number of arguments that SYMBOL-FUNCTION takes.
-    private static final int NUM_ARGS = 1;
+    private ArgumentValidator argumentValidator;
 
-    public SExpression call(Cons argList) {
-        // retrieve the number of arguments passed to SYMBOL-FUNCTION
-        int argListLength = LENGTH.getLength(argList);
+    public SYMBOL_FUNCTION() {
+        this.argumentValidator = new ArgumentValidator("SYMBOL-FUNCTION");
+        this.argumentValidator.setExactNumberOfArguments(1);
+        this.argumentValidator.setEveryArgumentExpectedType(Symbol.class);
+    }
 
-        // make sure we have received the proper number of arguments
-        if (argListLength != NUM_ARGS) {
-            Cons originalSExpr = new Cons(new Symbol("SYMBOL-FUNCTION"),
-                                          argList);
-            String errMsg = "too " +
-                            ((argListLength > NUM_ARGS) ? "many" : "few") +
-                            " arguments given to SYMBOL-FUNCTION: " +
-                            originalSExpr;
+    public SExpression call(Cons argumentList) {
+        argumentValidator.validate(argumentList);
 
-            throw new RuntimeException(errMsg);
+        SExpression symbol = argumentList.getCar();
+        LispFunction function = EVAL.lookupFunction(symbol.toString());
+
+        if (function != null) {
+            if (function instanceof UserDefinedFunction)
+                return ((UserDefinedFunction) function).getLambdaExpression();
+
+            return new Symbol(MessageFormat.format("#<SYSTEM-FUNCTION {0}>", symbol.toString()));
+        }
+        
+        throw new UndefinedSymbolFunctionException(symbol);
+    }
+
+    public static class UndefinedSymbolFunctionException extends LispException {
+
+        private static final long serialVersionUID = 1L;
+        private SExpression function;
+
+        public UndefinedSymbolFunctionException(SExpression function) {
+            this.function = function;
         }
 
-        SExpression arg = argList.getCar();
-
-        // make sure the argument is a symbol
-        if (arg.symbolp()) {
-            LispFunction function = EVAL.lookupFunction(arg.toString());
-
-            // make sure the function actually exists
-            if (function != null) {
-                if (function instanceof UserDefinedFunction) {
-                    // this is a user-defined function
-
-                    UserDefinedFunction udFunction = (UserDefinedFunction) function;
-
-                    return udFunction.getLambdaExpression();
-                }
-
-                // this is a built-in function
-
-                return new Symbol("SUBR-" + arg.toString());
-            }
-
-            throw new RuntimeException("SYMBOL-FUNCTION: undefined function " +
-                                       arg);
+        @Override
+        public String getMessage() {
+            return MessageFormat.format("SYMBOL-FUNCTION: undefined function: {0}", function);
         }
-
-        throw new RuntimeException("SYMBOL-FUNCTION: " + arg +
-                                   " is not a symbol");
     }
 
 }
diff --git a/test/function/builtin/EXITTester.java b/test/function/builtin/EXITTester.java
new file mode 100644
index 0000000..f0e8d0a
--- /dev/null
+++ b/test/function/builtin/EXITTester.java
@@ -0,0 +1,48 @@
+package function.builtin;
+
+import static org.junit.Assert.*;
+import static testutil.TestUtilities.evaluateString;
+
+import java.util.*;
+
+import org.junit.*;
+
+import environment.Environment;
+import function.ArgumentValidator.TooManyArgumentsException;
+
+public class EXITTester {
+
+    private static final String TERMINATED = "terminated";
+    private Set<String> indicatorSet;
+
+    private void assertTerminated() {
+        assertTrue(indicatorSet.contains(TERMINATED));
+    }
+
+    private void assertNotTerminated() {
+        assertFalse(indicatorSet.contains(TERMINATED));
+    }
+
+    @Before
+    public void setUp() {
+        indicatorSet = new HashSet<>();
+        Environment.getInstance().setTerminationFunction(() -> indicatorSet.add(TERMINATED));
+    }
+
+    @Test
+    public void exitWorks() {
+        evaluateString("(exit)");
+        assertTerminated();
+    }
+
+    @Test
+    public void exitNotCalled_IndicatorSetIsClean() {
+        assertNotTerminated();
+    }
+
+    @Test(expected = TooManyArgumentsException.class)
+    public void testExitWithTooManyArguments() {
+        evaluateString("(exit 1)");
+    }
+
+}
diff --git a/test/function/builtin/SYMBOL_FUNCTIONTester.java b/test/function/builtin/SYMBOL_FUNCTIONTester.java
new file mode 100644
index 0000000..593fbe0
--- /dev/null
+++ b/test/function/builtin/SYMBOL_FUNCTIONTester.java
@@ -0,0 +1,60 @@
+package function.builtin;
+
+import static org.junit.Assert.*;
+import static testutil.TestUtilities.evaluateString;
+
+import org.junit.Test;
+
+import function.ArgumentValidator.*;
+import function.builtin.SYMBOL_FUNCTION.UndefinedSymbolFunctionException;
+import sexpression.Nil;
+
+public class SYMBOL_FUNCTIONTester {
+
+    @Test
+    public void testSymbolFunction_BuiltinFunction() {
+        String input = "(symbol-function '+)";
+
+        assertEquals("#<SYSTEM-FUNCTION +>", evaluateString(input).toString());
+    }
+
+    @Test
+    public void testSymbolFunction_UserDefinedFunction() {
+        String defineUserFunction = "(defun y (n m) (+ n m))";
+        String input = "(symbol-function 'y)";
+
+        evaluateString(defineUserFunction);
+        assertEquals("(Y (N M) (+ N M))", evaluateString(input).toString());
+    }
+
+    @Test(expected = RuntimeException.class)
+    public void testSymbolFunction_NonFunction() {
+        String input = "(symbol-function 'a)";
+
+        evaluateString(input);
+    }
+
+    @Test(expected = BadArgumentTypeException.class)
+    public void testSymbolFunctionWithBadArgumentType() {
+        evaluateString("(symbol-function 2)");
+    }
+
+    @Test(expected = TooManyArgumentsException.class)
+    public void testSymbolFunctionWithTooManyArguments() {
+        evaluateString("(symbol-function 'a 'b)");
+    }
+
+    @Test(expected = TooFewArgumentsException.class)
+    public void testSymbolFunctionWithTooFewArguments() {
+        evaluateString("(symbol-function)");
+    }
+
+    @Test
+    public void undefinedSymbolFunctionException_HasMessageText() {
+        UndefinedSymbolFunctionException e = new UndefinedSymbolFunctionException(Nil.getInstance());
+
+        assertNotNull(e.getMessage());
+        assertTrue(e.getMessage().length() > 0);
+    }
+
+}