diff --git a/Object-Oriented Programming/Composition/Exercise 1/test/Tests.kt b/Object-Oriented Programming/Composition/Exercise 1/test/Tests.kt
index 2167d44b..6c4dcb3b 100644
--- a/Object-Oriented Programming/Composition/Exercise 1/test/Tests.kt	
+++ b/Object-Oriented Programming/Composition/Exercise 1/test/Tests.kt	
@@ -23,7 +23,7 @@ class TestCompositionExercise1 {
           "radius" to Int::class,
           "color" to String::class
       )
-      assertInheritance(this, listOf("Shape"))
+      assertInheritance("Shape")
     }
     loadClass(packageName, "Rectangle").apply {
       assertConstructorNumber(1)
@@ -32,7 +32,7 @@ class TestCompositionExercise1 {
           "width" to Int::class,
           "color" to String::class
       )
-      assertInheritance(this, listOf("Shape"))
+      assertInheritance("Shape")
     }
   }
 
diff --git a/Object-Oriented Programming/Polymorphism/Exercise 1/test/Tests.kt b/Object-Oriented Programming/Polymorphism/Exercise 1/test/Tests.kt
index d5b647f3..ed7b26e0 100644
--- a/Object-Oriented Programming/Polymorphism/Exercise 1/test/Tests.kt	
+++ b/Object-Oriented Programming/Polymorphism/Exercise 1/test/Tests.kt	
@@ -13,48 +13,48 @@ import kotlin.test.assertEquals
 @FixMethodOrder(MethodSorters.NAME_ASCENDING)
 class TestPolymorphismExercise1 {
 
-    private val packageName = "polymorphismExercise1"
+  private val packageName = "polymorphismExercise1"
 
-    @Test
-    fun `#01 classes structure`() {
-        loadClass(packageName, "Warrior").apply {
-            assertConstructorNumber(1)
-            assertInheritance(this, listOf("Character", "Fighter"))
-        }
-        loadClass(packageName, "Elf").apply {
-            assertConstructorNumber(1)
-            assertInheritance(this, listOf("Character", "Magician"))
-        }
-        loadClass(packageName, "FightingElf").apply {
-            assertConstructorNumber(1)
-            assertInheritance(this, listOf("Elf", "Fighter"))
-        }
-        loadClass(packageName, "Wizard").apply {
-            assertConstructorNumber(1)
-            assertInheritance(this, listOf("Character", "Magician", "Flyer"))
-        }
-        loadClass(packageName, "Dragon").apply {
-            assertConstructorNumber(1)
-            assertInheritance(this, listOf("Character", "Flyer"))
-        }
+  @Test
+  fun `#01 classes structure`() {
+    loadClass(packageName, "Warrior").apply {
+      assertConstructorNumber(1)
+      assertInheritance("Character", "Fighter")
     }
+    loadClass(packageName, "Elf").apply {
+      assertConstructorNumber(1)
+      assertInheritance("Character", "Magician")
+    }
+    loadClass(packageName, "FightingElf").apply {
+      assertConstructorNumber(1)
+      assertInheritance("Elf", "Fighter")
+    }
+    loadClass(packageName, "Wizard").apply {
+      assertConstructorNumber(1)
+      assertInheritance("Character", "Magician", "Flyer")
+    }
+    loadClass(packageName, "Dragon").apply {
+      assertConstructorNumber(1)
+      assertInheritance("Character", "Flyer")
+    }
+  }
 
-    @Test
-    fun `#02 what do the characters`() {
-        listOf("Warrior", "Elf", "FightingElf", "Dragon", "Wizard")
-                .map { loadClass(packageName, it).createInstance() as Character }
-                .forEach { c -> c.playTurn() }
+  @Test
+  fun `#02 what do the characters`() {
+    listOf("Warrior", "Elf", "FightingElf", "Dragon", "Wizard")
+        .map { loadClass(packageName, it).createInstance() as Character }
+        .forEach { c -> c.playTurn() }
 
-        assertEquals(
-                message = "Incorrect result of playTurn() for all characters",
-                actual = loadTraceContent(),
-                expected = listOf(
-                        "Warrior: Fight!",
-                        "Elf: Magic!",
-                        "FightingElf: Magic!Fight!",
-                        "Dragon: Fly!",
-                        "Magician: Magic!Fly!"
-                )
+    assertEquals(
+        message = "Incorrect result of playTurn() for all characters",
+        actual = loadTraceContent(),
+        expected = listOf(
+            "Warrior: Fight!",
+            "Elf: Magic!",
+            "FightingElf: Magic!Fight!",
+            "Dragon: Fly!",
+            "Magician: Magic!Fly!"
         )
-    }
+    )
+  }
 }
diff --git a/Object-Oriented Programming/Polymorphism/Exercise 2/test/Tests.kt b/Object-Oriented Programming/Polymorphism/Exercise 2/test/Tests.kt
index d3dddfdd..f7cb7155 100644
--- a/Object-Oriented Programming/Polymorphism/Exercise 2/test/Tests.kt	
+++ b/Object-Oriented Programming/Polymorphism/Exercise 2/test/Tests.kt	
@@ -22,7 +22,7 @@ class TestPolymorphismExercise2 {
         }
         loadClass(packageName, "Frog").apply {
             assertConstructorNumber(1)
-            assertInheritance(this, listOf("Animal"))
+            assertInheritance("Animal")
         }
     }
 
diff --git a/Object-Oriented Programming/Sealed Classes/Exercise 1/test/Tests.kt b/Object-Oriented Programming/Sealed Classes/Exercise 1/test/Tests.kt
index 561e469b..b4db3fc4 100644
--- a/Object-Oriented Programming/Sealed Classes/Exercise 1/test/Tests.kt	
+++ b/Object-Oriented Programming/Sealed Classes/Exercise 1/test/Tests.kt	
@@ -30,7 +30,7 @@ class TestSealedClassesExercise1 {
                 mainParameterName to String::class,
                 "capacity" to Int::class
             )
-            assertInheritance(this, listOf("Transport"))
+            assertInheritance("Transport")
         }
     }
 
diff --git a/util/test/util.kt b/util/test/util.kt
index bfb43e03..0342e588 100644
--- a/util/test/util.kt
+++ b/util/test/util.kt
@@ -141,15 +141,15 @@ fun assertInheritance(derivedClass: KClass<*>, baseClass: KClass<*>) {
     )
 }
 
-fun assertInheritance(derivedClass: KClass<*>, baseClassNames: List<String>) {
-    val packageName = derivedClass.qualifiedName!!
-            .removeSuffix(derivedClass.simpleName!!)
+fun KClass<*>.assertInheritance(vararg baseClassNames: String) {
+    val packageName = qualifiedName!!
+            .removeSuffix(simpleName!!)
             .removeSuffix(".")
     baseClassNames.forEach { className ->
         val baseClass = loadClass(packageName, className)
         assertTrue(
-                actual = derivedClass.supertypes.contains(baseClass.createType()),
-                message = "${derivedClass.simpleName} should inherit ${baseClass.simpleName}"
+                actual = supertypes.contains(baseClass.createType()),
+                message = "$simpleName should inherit ${baseClass.simpleName}"
         )
     }
 }