diff --git a/.classpath b/.classpath
index b52a479..5e3662d 100644
--- a/.classpath
+++ b/.classpath
@@ -2,11 +2,13 @@
 <classpath>
 	<classpathentry kind="src" path="src"/>
 	<classpathentry kind="src" path="test"/>
+	<classpathentry kind="src" path="acceptance"/>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.8">
 		<attributes>
 			<attribute name="owner.project.facets" value="java"/>
 		</attributes>
 	</classpathentry>
 	<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/4"/>
+	<classpathentry kind="lib" path="fitnesse/fitnesse-standalone.jar"/>
 	<classpathentry kind="output" path="build/classes"/>
 </classpath>
diff --git a/.gitignore b/.gitignore
index a61292a..c553637 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,6 @@
 build/
 doc/
+fitnesse/FitNesseRoot/files
 jar/
+*.zip
 *.swp
diff --git a/acceptance/fixture/LispInterpreterFixture.java b/acceptance/fixture/LispInterpreterFixture.java
new file mode 100644
index 0000000..50d53e7
--- /dev/null
+++ b/acceptance/fixture/LispInterpreterFixture.java
@@ -0,0 +1,48 @@
+package fixture;
+
+import java.io.*;
+
+import environment.RuntimeEnvironment;
+import interpreter.*;
+
+public class LispInterpreterFixture {
+
+    private ByteArrayOutputStream outputStream;
+    private RuntimeEnvironment environment;
+    private LispInterpreter interpreter;
+
+    public LispInterpreterFixture() throws IOException {
+        this.outputStream = new ByteArrayOutputStream();
+        this.environment = RuntimeEnvironment.getInstance();
+        this.interpreter = buildInterpreter();
+    }
+
+    private LispInterpreter buildInterpreter() {
+        LispInterpreterBuilder builder = LispInterpreterBuilderImpl.getInstance();
+        builder.setInputName("fitnesse");
+        builder.setOutput(new PrintStream(outputStream));
+        builder.setErrorOutput(new PrintStream(outputStream));
+        builder.setNotInteractive();
+        builder.setTerminationFunction(() -> System.exit(0));
+        builder.setErrorTerminationFunction(() -> System.exit(1));
+
+        return builder.build();
+    }
+
+    public void input(String input) throws IOException {
+        environment.setInput(new ByteArrayInputStream(input.getBytes()));
+        interpreter.interpret();
+    }
+
+    public String output() {
+        String output = outputStream.toString();
+        discardOutput();
+
+        return output;
+    }
+
+    public void discardOutput() {
+        outputStream.reset();
+    }
+
+}
diff --git a/fitnesse/fitnesse-standalone.jar b/fitnesse/fitnesse-standalone.jar
new file mode 100644
index 0000000..1effc39
Binary files /dev/null and b/fitnesse/fitnesse-standalone.jar differ
diff --git a/src/interpreter/InteractiveLispInterpreter.java b/src/interpreter/InteractiveLispInterpreter.java
index 14080a0..95cd1f5 100644
--- a/src/interpreter/InteractiveLispInterpreter.java
+++ b/src/interpreter/InteractiveLispInterpreter.java
@@ -7,26 +7,26 @@ public class InteractiveLispInterpreter extends LispInterpreter {
 
     @Override
     protected void printGreeting() {
-        environment.getOutput().println(GREETING);
-        environment.getOutput().println();
+        output.println(GREETING);
+        output.println();
     }
 
     @Override
     protected void displayPrompt() {
-        environment.getOutput().print(PROMPT);
+        output.print(PROMPT);
     }
 
     @Override
     protected void erasePrompt() {
         for (int i = 0; i < PROMPT.length(); i++) {
-            environment.getOutput().print("\b");
+            output.print("\b");
         }
     }
 
     @Override
     protected void printFarewell() {
-        environment.getOutput().println();
-        environment.getOutput().println();
+        output.println();
+        output.println();
     }
 
 }
diff --git a/src/interpreter/LispInterpreter.java b/src/interpreter/LispInterpreter.java
index 3462ec9..90c884a 100644
--- a/src/interpreter/LispInterpreter.java
+++ b/src/interpreter/LispInterpreter.java
@@ -2,6 +2,8 @@ package interpreter;
 
 import static function.builtin.EVAL.eval;
 
+import java.io.PrintStream;
+
 import environment.RuntimeEnvironment;
 import error.*;
 import parser.LispParser;
@@ -11,15 +13,17 @@ public class LispInterpreter {
 
     protected RuntimeEnvironment environment;
     protected ErrorManager errorManager;
+    protected PrintStream output;
     private LispParser parser;
 
     public LispInterpreter() {
         this.environment = RuntimeEnvironment.getInstance();
         this.errorManager = this.environment.getErrorManager();
-        this.parser = new LispParser(this.environment.getInput(), this.environment.getInputName());
+        this.output = environment.getOutput();
     }
 
     public void interpret() {
+        createParser();
         printGreeting();
 
         for (displayPrompt(); !parser.isEof(); displayPrompt())
@@ -28,6 +32,10 @@ public class LispInterpreter {
         printFarewell();
     }
 
+    private void createParser() {
+        parser = new LispParser(environment.getInput(), environment.getInputName());
+    }
+
     protected void printGreeting() {}
 
     protected void displayPrompt() {}
@@ -46,13 +54,13 @@ public class LispInterpreter {
         String result = environment.decorateValueOutput(String.valueOf(eval(sExpression)));
 
         erasePrompt();
-        environment.getOutput().println(result);
+        output.println(result);
     }
 
     protected void erasePrompt() {}
 
     protected void printFarewell() {
-        environment.getOutput().println();
+        output.println();
     }
 
 }
diff --git a/src/interpreter/LispInterpreterBuilder.java b/src/interpreter/LispInterpreterBuilder.java
index cad2659..6a8f8d9 100644
--- a/src/interpreter/LispInterpreterBuilder.java
+++ b/src/interpreter/LispInterpreterBuilder.java
@@ -16,6 +16,8 @@ public interface LispInterpreterBuilder {
     void setTerminationFunction(Runnable terminationFunction);
 
     void setErrorTerminationFunction(Runnable errorTerminationFunction);
+    
+    void setNotInteractive();
 
     void useFile(String fileName);
 
diff --git a/src/interpreter/LispInterpreterBuilderImpl.java b/src/interpreter/LispInterpreterBuilderImpl.java
index 8cf7e17..eb87d60 100644
--- a/src/interpreter/LispInterpreterBuilderImpl.java
+++ b/src/interpreter/LispInterpreterBuilderImpl.java
@@ -27,12 +27,14 @@ public class LispInterpreterBuilderImpl implements LispInterpreterBuilder {
     private Function<String, String> criticalOutputDecorator;
     private RuntimeEnvironment environment;
     private boolean isInteractive;
+    private boolean isUseFile;
     private boolean isBuilt;
 
     private LispInterpreterBuilderImpl() {
         this.environment = RuntimeEnvironment.getInstance();
         this.inputName = "";
         this.isInteractive = true;
+        this.isUseFile = false;
         this.isBuilt = false;
         this.outputDecorator = s -> s;
         this.valueOutputDecorator = s -> s;
@@ -73,11 +75,17 @@ public class LispInterpreterBuilderImpl implements LispInterpreterBuilder {
     }
 
     @Override
-    public void useFile(String fileName) {
-        this.inputName = fileName;
+    public void setNotInteractive() {
         this.isInteractive = false;
     }
 
+    @Override
+    public void useFile(String fileName) {
+        this.isUseFile = true;
+        this.setInputName(fileName);
+        this.setNotInteractive();
+    }
+
     @Override
     public void setOutputDecorator(Function<String, String> decorator) {
         this.outputDecorator = decorator;
@@ -148,7 +156,7 @@ public class LispInterpreterBuilderImpl implements LispInterpreterBuilder {
     }
 
     private InputStream getInputStream() throws FileNotFoundException {
-        return isInteractive ? inputStream : new FileInputStream(inputName);
+        return isUseFile ? new FileInputStream(inputName) : inputStream;
     }
 
     private LispInterpreter createInterpreter() {