diff --git a/pom.xml b/pom.xml
index 14b464f..f8a982c 100644
--- a/pom.xml
+++ b/pom.xml
@@ -127,6 +127,13 @@
             <version>5.7.0</version>
             <scope>test</scope>
         </dependency>
+
+        <dependency>
+            <groupId>nl.jqno.equalsverifier</groupId>
+            <artifactId>equalsverifier</artifactId>
+            <version>3.5.2</version>
+            <scope>test</scope>
+        </dependency>
         <!-- need these for IntelliJ -->
         <dependency>
             <groupId>org.junit.platform</groupId>
diff --git a/src/test/java/edu/kit/typicalc/model/ConstraintTest.java b/src/test/java/edu/kit/typicalc/model/ConstraintTest.java
new file mode 100644
index 0000000..71deee8
--- /dev/null
+++ b/src/test/java/edu/kit/typicalc/model/ConstraintTest.java
@@ -0,0 +1,32 @@
+package edu.kit.typicalc.model;
+
+import edu.kit.typicalc.model.type.Type;
+import edu.kit.typicalc.model.type.TypeVariable;
+import edu.kit.typicalc.model.type.TypeVaribaleKind;
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ConstraintTest {
+
+    private static final Type type1 = new TypeVariable(TypeVaribaleKind.USER_INPUT, 1);
+    private static final Type type2 = new TypeVariable(TypeVaribaleKind.TREE, 2);
+
+    @Test
+    void equalsTest() {
+        EqualsVerifier.forClass(Constraint.class).usingGetClass().verify();
+    }
+
+    @Test
+    void getFirstTest() {
+        Constraint con = new Constraint(type1,type2);
+        assertEquals(type1, con.getFirstType());
+    }
+
+    @Test
+    void getSecondTest() {
+        Constraint con = new Constraint(type1,type2);
+        assertEquals(type2, con.getSecondType());
+    }
+}
diff --git a/src/test/java/edu/kit/typicalc/model/SubstitutionTest.java b/src/test/java/edu/kit/typicalc/model/SubstitutionTest.java
new file mode 100644
index 0000000..98c34c8
--- /dev/null
+++ b/src/test/java/edu/kit/typicalc/model/SubstitutionTest.java
@@ -0,0 +1,32 @@
+package edu.kit.typicalc.model;
+
+import edu.kit.typicalc.model.type.Type;
+import edu.kit.typicalc.model.type.TypeVariable;
+import edu.kit.typicalc.model.type.TypeVaribaleKind;
+import nl.jqno.equalsverifier.EqualsVerifier;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class SubstitutionTest {
+
+    private static final TypeVariable var = new TypeVariable(TypeVaribaleKind.USER_INPUT, 1);
+    private static final Type type = new TypeVariable(TypeVaribaleKind.TREE, 2);
+
+    @Test
+    void equalsTest() {
+        EqualsVerifier.forClass(Substitution.class).usingGetClass().verify();
+    }
+
+    @Test
+    void getVariableTest() {
+        Substitution sub = new Substitution(var,type);
+        assertEquals(var, sub.getVariable());
+    }
+
+    @Test
+    void getTypeTest() {
+        Substitution sub = new Substitution(var,type);
+        assertEquals(type, sub.getType());
+    }
+}
diff --git a/src/test/java/edu/kit/typicalc/model/type/FunctionTypeTest.java b/src/test/java/edu/kit/typicalc/model/type/FunctionTypeTest.java
index c76964b..eaa1f88 100644
--- a/src/test/java/edu/kit/typicalc/model/type/FunctionTypeTest.java
+++ b/src/test/java/edu/kit/typicalc/model/type/FunctionTypeTest.java
@@ -1,11 +1,17 @@
 package edu.kit.typicalc.model.type;
 
+import nl.jqno.equalsverifier.EqualsVerifier;
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
 
 class FunctionTypeTest {
 
+    @Test
+    void equalsTest() {
+        EqualsVerifier.forClass(FunctionType.class).usingGetClass().verify();
+    }
+
     @Test
     void substitute() {
         TypeVariable typeVariable1 = new TypeVariable(TypeVaribaleKind.USER_INPUT, 1);