diff --git a/src/main/scala/de/retest/guistatemachine/model/GuiApplications.scala b/src/main/scala/de/retest/guistatemachine/model/GuiApplications.scala
index 9da2b30..3d85201 100644
--- a/src/main/scala/de/retest/guistatemachine/model/GuiApplications.scala
+++ b/src/main/scala/de/retest/guistatemachine/model/GuiApplications.scala
@@ -1,6 +1,3 @@
 package de.retest.guistatemachine.model
 
-final case class GuiApplications(applications: Map[GuiApplication]) {
-  // TODO Generate IDs in a better way. Maybe random numbers until one unused element is found?
-  def generateId: Id = this.synchronized { if (applications.values.isEmpty) Id(0) else Id(applications.values.keySet.max.id + 1) }
-}
\ No newline at end of file
+final case class GuiApplications(var values: scala.collection.immutable.Map[Id, GuiApplication]) extends Map[GuiApplication](values)
\ No newline at end of file
diff --git a/src/main/scala/de/retest/guistatemachine/model/Map.scala b/src/main/scala/de/retest/guistatemachine/model/Map.scala
index b67cf77..8185acc 100644
--- a/src/main/scala/de/retest/guistatemachine/model/Map.scala
+++ b/src/main/scala/de/retest/guistatemachine/model/Map.scala
@@ -5,6 +5,13 @@ package de.retest.guistatemachine.model
  * [[JsonFormatForIdMap]] implements marshalling and unmarshalling for JSON for this type.
  * We cannot extend immutable maps in Scala, so we have to keep it as field.
  */
-case class Map[T](var values: scala.collection.immutable.Map[Id, T]) {
+class Map[T](var values: scala.collection.immutable.Map[Id, T]) {
+  /**
+   * Generates a new ID based on the existing entries.
+   * TODO Generate IDs in a better way. Maybe random numbers until one unused element is found?
+   */
+  def generateId: Id = this.synchronized { if (values.isEmpty) Id(0) else Id(values.keySet.max.id + 1) }
 
+  def setValues(v: scala.collection.immutable.Map[Id, T]) { values = v }
+  def getValues: scala.collection.immutable.Map[Id, T] = values
 }
\ No newline at end of file
diff --git a/src/main/scala/de/retest/guistatemachine/model/TestSuites.scala b/src/main/scala/de/retest/guistatemachine/model/TestSuites.scala
index 52c855c..3eb47bd 100644
--- a/src/main/scala/de/retest/guistatemachine/model/TestSuites.scala
+++ b/src/main/scala/de/retest/guistatemachine/model/TestSuites.scala
@@ -1,6 +1,3 @@
 package de.retest.guistatemachine.model
 
-final case class TestSuites(testSuites: Map[TestSuite]) {
-  // TODO Generate IDs in a better way. Maybe random numbers until one unused element is found?
-  def generateId: Id = this.synchronized { if (testSuites.values.isEmpty) Id(0) else Id(testSuites.values.keySet.max.id + 1) }
-}
\ No newline at end of file
+final case class TestSuites(var values: scala.collection.immutable.Map[Id, TestSuite]) extends Map[TestSuite](values)
\ No newline at end of file
diff --git a/src/main/scala/de/retest/guistatemachine/persistence/Persistence.scala b/src/main/scala/de/retest/guistatemachine/persistence/Persistence.scala
index 73c7d51..1617764 100644
--- a/src/main/scala/de/retest/guistatemachine/persistence/Persistence.scala
+++ b/src/main/scala/de/retest/guistatemachine/persistence/Persistence.scala
@@ -15,7 +15,7 @@ import de.retest.guistatemachine.model.Map
  */
 class Persistence {
   // database
-  private val guiApplications = GuiApplications(Map[GuiApplication](new HashMap[Id, GuiApplication]))
+  private val guiApplications = GuiApplications(new HashMap[Id, GuiApplication])
 
   def getApplications(): GuiApplications = guiApplications
 
@@ -23,14 +23,14 @@ class Persistence {
     val apps = guiApplications
     apps.synchronized {
       val id = apps.generateId
-      apps.applications.values = apps.applications.values + (id -> new GuiApplication(TestSuites(Map[TestSuite](new HashMap[Id, TestSuite]))))
+      apps.setValues(apps.getValues + (id -> new GuiApplication(TestSuites(new HashMap[Id, TestSuite]))))
       id
     }
   }
   def getApplication(id: Id): Option[GuiApplication] = {
     val apps = guiApplications
     apps.synchronized {
-      if (apps.applications.values.contains(id)) Some(apps.applications.values(id)) else { None }
+      if (apps.values.contains(id)) Some(apps.values(id)) else { None }
     }
   }
 
@@ -49,7 +49,7 @@ class Persistence {
         val testSuites = x.testSuites
         testSuites.synchronized {
           val id = testSuites.generateId
-          testSuites.testSuites.values = testSuites.testSuites.values + (id -> TestSuite())
+          testSuites.setValues(testSuites.getValues + (id -> TestSuite()))
           Some(id)
         }
       }
@@ -62,7 +62,7 @@ class Persistence {
       case Some(x) => {
         val testSuites = x.testSuites
         testSuites.synchronized {
-          if (testSuites.testSuites.values.contains(testSuiteId)) Some(testSuites.testSuites.values(testSuiteId)) else None
+          if (testSuites.values.contains(testSuiteId)) Some(testSuites.values(testSuiteId)) else None
         }
       }
       case None => None
diff --git a/src/test/scala/de/retest/guistatemachine/RestServiceSpec.scala b/src/test/scala/de/retest/guistatemachine/RestServiceSpec.scala
index 861b055..ef17bd5 100644
--- a/src/test/scala/de/retest/guistatemachine/RestServiceSpec.scala
+++ b/src/test/scala/de/retest/guistatemachine/RestServiceSpec.scala
@@ -34,7 +34,7 @@ class RestServiceSpec extends WordSpec with Matchers with ScalatestRouteTest wit
         handled shouldEqual true
         mediaType shouldEqual MediaTypes.`application/json`
         val r = responseAs[GuiApplications]
-        r.applications.values.size shouldEqual 0
+        r.values.size shouldEqual 0
       }
     }
 
@@ -47,15 +47,16 @@ class RestServiceSpec extends WordSpec with Matchers with ScalatestRouteTest wit
     "return an empty application for the GET request with the path /application/0" in {
       Get("/applications/0") ~> sut ~> check {
         // TODO Print response here
+        println("Response: " + responseAs[String])
         val r = responseAs[GuiApplication]
-        r.testSuites.testSuites.values.size shouldEqual 0
+        r.testSuites.values.size shouldEqual 0
       }
     }
 
     "return an empty list for the GET request with the path /application/0/test-suites" in {
       Get("/applications/0/test-suites") ~> sut ~> check {
         val r = responseAs[TestSuites]
-        r.testSuites.values.size shouldEqual 0
+        r.values.size shouldEqual 0
       }
     }
 
diff --git a/src/test/scala/de/retest/guistatemachine/persistence/PersistenceSpec.scala b/src/test/scala/de/retest/guistatemachine/persistence/PersistenceSpec.scala
index 3efaf75..3688753 100644
--- a/src/test/scala/de/retest/guistatemachine/persistence/PersistenceSpec.scala
+++ b/src/test/scala/de/retest/guistatemachine/persistence/PersistenceSpec.scala
@@ -9,12 +9,12 @@ class PersistenceSpec extends WordSpec with Matchers {
 
   "The pesistence" should {
     "allow adding one test suite" in {
-      sut.getApplications().applications.values.size shouldEqual 0
+      sut.getApplications().values.size shouldEqual 0
       sut.addApplication().id shouldEqual 0
-      sut.getApplications().applications.values.size shouldEqual 1
-      sut.getTestSuites(Id(0)).get.testSuites.values.size shouldEqual 0
+      sut.getApplications().values.size shouldEqual 1
+      sut.getTestSuites(Id(0)).get.values.size shouldEqual 0
       sut.addTestSuite(Id(0)).get.id shouldEqual 0
-      sut.getTestSuites(Id(0)).get.testSuites.values.size shouldEqual 1
+      sut.getTestSuites(Id(0)).get.values.size shouldEqual 1
       val s = sut.getTestSuite(Id(0), Id(0))
       s.isEmpty shouldEqual false
     }