Index: /ModelExtender/.classpath
===================================================================
--- /ModelExtender/.classpath	(revision 195)
+++ /ModelExtender/.classpath	(revision 196)
@@ -2,8 +2,10 @@
 <classpath>
 	<classpathentry kind="src" path="src"/>
+	<classpathentry kind="src" path="test"/>
 	<classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/JavaSE-1.7"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/Model"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/Utils"/>
 	<classpathentry combineaccessrules="false" kind="src" path="/ModelTranslator"/>
+	<classpathentry kind="con" path="org.eclipse.jdt.junit.JUNIT_CONTAINER/4"/>
 	<classpathentry kind="output" path="bin"/>
 </classpath>
Index: /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/AllTests.java
===================================================================
--- /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/AllTests.java	(revision 196)
+++ /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/AllTests.java	(revision 196)
@@ -0,0 +1,16 @@
+package de.uni_hildesheim.de.see.model_extender.test;
+
+import org.junit.runner.RunWith;
+import org.junit.runners.Suite;
+import org.junit.runners.Suite.SuiteClasses;
+
+/**
+ * Runs all tests.
+ * 
+ * @author Adam Krafczyk
+ */
+@RunWith(Suite.class)
+@SuiteClasses({ ModelExtenderTest.class })
+public class AllTests {
+
+}
Index: /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/ModelExtenderTest.java
===================================================================
--- /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/ModelExtenderTest.java	(revision 196)
+++ /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/ModelExtenderTest.java	(revision 196)
@@ -0,0 +1,102 @@
+package de.uni_hildesheim.de.see.model_extender.test;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+
+import junit.framework.Assert;
+
+import org.junit.Test;
+
+import de.uni_hildesheim.sse.model.varModel.Project;
+import de.uni_hildesheim.sse.model.varModel.filter.ConstraintFinder;
+import de.uni_hildesheim.sse.model.varModel.filter.DeclarationFinder;
+import de.uni_hildesheim.sse.model.varModel.filter.FilterType;
+import de.uni_hildesheim.sse.model.varModel.filter.DeclarationFinder.VisibilityType;
+import de.uni_hildesheim.sse.model_extender.convert.ModelExtender;
+import de.uni_hildesheim.sse.model_extender.in.DimacsReader;
+import de.uni_hildesheim.sse.model_extender.in.MalformedFileException;
+import de.uni_hildesheim.sse.trans.in.ParserException;
+
+/**
+ * Class for testing the {@link ModelExtender}.
+ * 
+ * @author Adam Krafczyk
+ */
+public class ModelExtenderTest {
+
+    /**
+     * Tests whether constraints are added correctly to the model.
+     */
+    @Test
+    public void testAddConstraints() {
+        try {
+            Project model = loadModel("testdata/testAddConstraint.dimacs");
+            
+            ModelExtender extender = new ModelExtender(model);
+            
+            DeclarationFinder declFinder = new DeclarationFinder(model, FilterType.ALL, null);
+            Assert.assertEquals(0, declFinder.getVariableDeclarations(VisibilityType.ALL).size());
+            
+            ConstraintFinder constraintFinder = new ConstraintFinder(model);
+            Assert.assertEquals(0, constraintFinder.getConstraints().size());
+            
+            extender.addConstraint("A || B");
+            
+            declFinder = new DeclarationFinder(model, FilterType.ALL, null);
+            Assert.assertEquals(2, declFinder.getVariableDeclarations(VisibilityType.ALL).size());
+            
+            constraintFinder = new ConstraintFinder(model);
+            Assert.assertEquals(1, constraintFinder.getConstraints().size());
+            
+        } catch (IOException | MalformedFileException | ParserException e) {
+            e.printStackTrace();
+            Assert.fail();
+        }
+    }
+    
+    /**
+     * Tests whether the newly added constraints use the existing variables.
+     */
+    @Test
+    public void testUseExistingVariables() {
+        try {
+            Project model = loadModel("testdata/testUseExistingVariables.dimacs");
+            
+            ModelExtender extender = new ModelExtender(model);
+            
+            DeclarationFinder declFinder = new DeclarationFinder(model, FilterType.ALL, null);
+            Assert.assertEquals(2, declFinder.getVariableDeclarations(VisibilityType.ALL).size());
+            
+            ConstraintFinder constraintFinder = new ConstraintFinder(model);
+            Assert.assertEquals(0, constraintFinder.getConstraints().size());
+            
+            extender.addConstraint("A || B || C");
+            
+            declFinder = new DeclarationFinder(model, FilterType.ALL, null);
+            Assert.assertEquals(3, declFinder.getVariableDeclarations(VisibilityType.ALL).size());
+            
+            constraintFinder = new ConstraintFinder(model);
+            Assert.assertEquals(1, constraintFinder.getConstraints().size());
+            
+        } catch (IOException | MalformedFileException | ParserException e) {
+            e.printStackTrace();
+            Assert.fail();
+        }
+    }
+    
+    /**
+     * Loads the given model from a .dimacs file.
+     * 
+     * @param filename The filename of the model.
+     * @return The model.
+     * 
+     * @throws MalformedFileException 
+     * @throws IOException 
+     * @throws FileNotFoundException 
+     */
+    private Project loadModel(String filename) throws FileNotFoundException, IOException, MalformedFileException {
+        return new DimacsReader(new File(filename)).getModel();
+    }
+    
+}
Index: /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/package-info.java
===================================================================
--- /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/package-info.java	(revision 196)
+++ /ModelExtender/test/de/uni_hildesheim/de/see/model_extender/test/package-info.java	(revision 196)
@@ -0,0 +1,4 @@
+/**
+ * Contains classes for testing the ModelExtender.
+ */
+package de.uni_hildesheim.de.see.model_extender.test;
Index: /ModelExtender/testdata/testAddConstraint.dimacs
===================================================================
--- /ModelExtender/testdata/testAddConstraint.dimacs	(revision 196)
+++ /ModelExtender/testdata/testAddConstraint.dimacs	(revision 196)
@@ -0,0 +1,1 @@
+p CNF 0 0
Index: /ModelExtender/testdata/testUseExistingVariables.dimacs
===================================================================
--- /ModelExtender/testdata/testUseExistingVariables.dimacs	(revision 196)
+++ /ModelExtender/testdata/testUseExistingVariables.dimacs	(revision 196)
@@ -0,0 +1,3 @@
+c 1 A
+c 2 B
+p CNF 2 0