diff --git a/backend/.idea/workspace.xml b/backend/.idea/workspace.xml
index 3e12b67..e60b4fc 100644
--- a/backend/.idea/workspace.xml
+++ b/backend/.idea/workspace.xml
@@ -4,10 +4,16 @@
     <option name="autoReloadType" value="SELECTIVE" />
   </component>
   <component name="ChangeListManager">
-    <list default="true" id="3a869f59-290a-4ab2-b036-a878ce801bc4" name="Changes" comment="Resolve Merge-Conflict">
+    <list default="true" id="3a869f59-290a-4ab2-b036-a878ce801bc4" name="Changes" comment="Testcases (and failing test fixes) of TaskgroupService">
+      <change afterPath="$PROJECT_DIR$/src/test/java/core/tasks/TaskServiceTest.java" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/.idea/workspace.xml" beforeDir="false" afterPath="$PROJECT_DIR$/.idea/workspace.xml" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/main/java/core/api/models/timemanager/tasks/TaskFieldInfo.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/core/api/models/timemanager/tasks/TaskFieldInfo.java" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/main/java/core/entities/timemanager/Task.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/core/entities/timemanager/Task.java" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/main/java/core/entities/timemanager/Taskgroup.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/core/entities/timemanager/Taskgroup.java" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/main/java/core/services/ServiceExitCode.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/core/services/ServiceExitCode.java" afterDir="false" />
       <change beforePath="$PROJECT_DIR$/src/main/java/core/services/TaskService.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/main/java/core/services/TaskService.java" afterDir="false" />
-      <change beforePath="$PROJECT_DIR$/src/test/java/core/tasks/TaskServiceTest.java" beforeDir="false" afterPath="$PROJECT_DIR$/src/test/java/core/tasks/TaskServiceTest.java" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/test/resources/application.properties" beforeDir="false" afterPath="$PROJECT_DIR$/src/test/resources/application.properties" afterDir="false" />
+      <change beforePath="$PROJECT_DIR$/src/test/resources/taskRepositoryEntries.sql" beforeDir="false" afterPath="$PROJECT_DIR$/src/test/resources/taskRepositoryEntries.sql" afterDir="false" />
     </list>
     <option name="SHOW_DIALOG" value="false" />
     <option name="HIGHLIGHT_CONFLICTS" value="true" />
@@ -26,7 +32,7 @@
   <component name="Git.Settings">
     <option name="RECENT_BRANCH_BY_REPOSITORY">
       <map>
-        <entry key="$PROJECT_DIR$/.." value="test-failing" />
+        <entry key="$PROJECT_DIR$/.." value="master" />
       </map>
     </option>
     <option name="RECENT_GIT_ROOT_PATH" value="$PROJECT_DIR$/.." />
@@ -86,8 +92,8 @@
       <recent name="$PROJECT_DIR$/src/test/java/core/taskgroups" />
     </key>
   </component>
-  <component name="RunManager" selected="JUnit.TaskRepositoryTest">
-    <configuration name="TaskRepositoryTest" type="JUnit" factoryName="JUnit" temporary="true" nameIsGenerated="true">
+  <component name="RunManager" selected="JUnit.TaskgroupServiceTest">
+    <configuration name="TaskRepositoryTest.deleteByTaskID" type="JUnit" factoryName="JUnit" temporary="true" nameIsGenerated="true">
       <module name="demo" />
       <extension name="coverage">
         <pattern>
@@ -97,7 +103,8 @@
       </extension>
       <option name="PACKAGE_NAME" value="core.tasks" />
       <option name="MAIN_CLASS_NAME" value="core.tasks.TaskRepositoryTest" />
-      <option name="TEST_OBJECT" value="class" />
+      <option name="METHOD_NAME" value="deleteByTaskID" />
+      <option name="TEST_OBJECT" value="method" />
       <method v="2">
         <option name="Make" enabled="true" />
       </method>
@@ -173,11 +180,11 @@
     </configuration>
     <recent_temporary>
       <list>
-        <item itemvalue="JUnit.TaskRepositoryTest" />
         <item itemvalue="JUnit.TaskgroupServiceTest" />
         <item itemvalue="JUnit.TaskServiceTest" />
-        <item itemvalue="JUnit.TaskServiceTest.deleteTask" />
         <item itemvalue="JUnit.TaskServiceTest.createTask" />
+        <item itemvalue="JUnit.TaskServiceTest.deleteTask" />
+        <item itemvalue="JUnit.TaskRepositoryTest.deleteByTaskID" />
       </list>
     </recent_temporary>
   </component>
@@ -215,7 +222,7 @@
       <workItem from="1699466564154" duration="6646000" />
       <workItem from="1699473376129" duration="1423000" />
       <workItem from="1699639316405" duration="9267000" />
-      <workItem from="1699684493731" duration="1121000" />
+      <workItem from="1699684493731" duration="7709000" />
     </task>
     <task id="LOCAL-00001" summary="Structure Taskgroups in Hierarchies">
       <option name="closed" value="true" />
@@ -449,13 +456,13 @@
       <option name="project" value="LOCAL" />
       <updated>1699646291964</updated>
     </task>
-    <task id="LOCAL-00030" summary="Resolve Merge-Conflict">
+    <task id="LOCAL-00030" summary="Testcases (and failing test fixes) of TaskgroupService">
       <option name="closed" value="true" />
-      <created>1699693472182</created>
+      <created>1699685656297</created>
       <option name="number" value="00030" />
       <option name="presentableId" value="LOCAL-00030" />
       <option name="project" value="LOCAL" />
-      <updated>1699693472182</updated>
+      <updated>1699685656297</updated>
     </task>
     <option name="localTasksCounter" value="31" />
     <servers />
@@ -464,6 +471,7 @@
     <option name="version" value="3" />
   </component>
   <component name="VcsManagerConfiguration">
+    <MESSAGE value="Define Entity BasicTaskSchedule and Taskcontroller" />
     <MESSAGE value="Delete Schedules" />
     <MESSAGE value="Deliver Schedule Path Info when fetching Schedules" />
     <MESSAGE value="Removed unused TaskgroupShortInfo.java" />
@@ -487,9 +495,8 @@
     <MESSAGE value="Test TaskRepository" />
     <MESSAGE value="Initialize Testing of Testservice" />
     <MESSAGE value="Use @Sql instead of persit()" />
-    <MESSAGE value="Make the Test Transactional" />
-    <MESSAGE value="Resolve Merge-Conflict" />
-    <option name="LAST_COMMIT_MESSAGE" value="Resolve Merge-Conflict" />
+    <MESSAGE value="Testcases (and failing test fixes) of TaskgroupService" />
+    <option name="LAST_COMMIT_MESSAGE" value="Testcases (and failing test fixes) of TaskgroupService" />
   </component>
   <component name="XDebuggerManager">
     <breakpoint-manager>
@@ -514,6 +521,11 @@
           <line>57</line>
           <option name="timeStamp" value="12" />
         </line-breakpoint>
+        <line-breakpoint enabled="true" type="java-line">
+          <url>file://$PROJECT_DIR$/src/test/java/core/tasks/TaskServiceTest.java</url>
+          <line>188</line>
+          <option name="timeStamp" value="23" />
+        </line-breakpoint>
       </breakpoints>
     </breakpoint-manager>
   </component>
diff --git a/backend/src/main/java/core/services/TaskService.java b/backend/src/main/java/core/services/TaskService.java
index 278a69f..3f74b82 100644
--- a/backend/src/main/java/core/services/TaskService.java
+++ b/backend/src/main/java/core/services/TaskService.java
@@ -79,6 +79,12 @@ public class TaskService {
             }
         }
 
+        //Check for invalid date (deadline before start
+        if(taskFieldInfo.getStartDate() != null && taskFieldInfo.getDeadline() != null &&
+                taskFieldInfo.getDeadline().isBefore(taskFieldInfo.getStartDate())) {
+            return new ServiceResult<>(ServiceExitCode.INVALID_PARAMETER);
+        }
+
         //Check for invalid date (deadline before start
         if(taskFieldInfo.getStartDate() != null && taskFieldInfo.getDeadline() != null &&
                 taskFieldInfo.getDeadline().isBefore(taskFieldInfo.getStartDate())) {
diff --git a/backend/src/test/java/core/tasks/TaskServiceTest.java b/backend/src/test/java/core/tasks/TaskServiceTest.java
index 1cd88a9..052014b 100644
--- a/backend/src/test/java/core/tasks/TaskServiceTest.java
+++ b/backend/src/test/java/core/tasks/TaskServiceTest.java
@@ -43,6 +43,10 @@ public class TaskServiceTest {
             @Sql("classpath:taskgroupRepositoryTestEntries.sql"),
             @Sql("classpath:taskRepositoryEntries.sql")
     })
+<<<<<<< HEAD
+=======
+    @Rollback(value = true)
+>>>>>>> 5e39cb1 (TaskService Test will fail)
     void createTask() {
         //Situation 1: Task with that name already exists in a taskgroup
         TaskFieldInfo taskFieldInfo_1 = new TaskFieldInfo(entityManager.find(Task.class, 1L).getTaskName(), 0, null, null);
@@ -118,58 +122,99 @@ public class TaskServiceTest {
         assertEquals(ServiceExitCode.OK, result_1.getExitCode());
         assertEquals(task_1, result_1.getResult());
 
+<<<<<<< HEAD
         //Situation 2: Name is updated to name that already exists within the taskgroup
         Task task_2 = entityManager.find(Task.class, 1L);
         TaskFieldInfo taskFieldInfo_2 = new TaskFieldInfo(entityManager.find(Task.class, 2L).getTaskName(), 0, null, null);
         ServiceResult<Task> result_2 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_2);
         task_2.setTaskName(entityManager.find(Task.class, 2L).getTaskName());
+=======
+        //Situation 2: Name is updated to name that already exists within another taskgroup
+        Task task_2 = entityManager.find(Task.class, 1L);
+        task_2.setTaskName(entityManager.find(Task.class, 2L).getTaskName());
+        TaskFieldInfo taskFieldInfo_2 = new TaskFieldInfo(entityManager.find(Task.class, 2L).getTaskName(), 0, null, null);
+        ServiceResult<Task> result_2 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_2);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.ENTITY_ALREADY_EXIST, result_2.getExitCode());
         assertNotEquals(task_2, result_2.getResult());
 
         //Situation 3: Name is updated to nonexistend Name
         Task task_3 = entityManager.find(Task.class, 1L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_3 = new TaskFieldInfo("Situation 3", 0, null, null);
         ServiceResult<Task> result_3 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_3);
         task_3.setTaskName("Situation 3");
+=======
+        task_3.setTaskName("Situation 3");
+        TaskFieldInfo taskFieldInfo_3 = new TaskFieldInfo("Situation 3", 0, null, null);
+        ServiceResult<Task> result_3 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_3);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.OK, result_3.getExitCode());
         assertEquals(task_3, result_3.getResult());
 
         //Situation 4: eta is updated
         Task task_4 = entityManager.find(Task.class, 1L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_4 = new TaskFieldInfo(task_4.getTaskName(), 90, null, null);
         ServiceResult<Task> result_4 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_4);
         task_4.setEta(90);
+=======
+        task_4.setEta(90);
+        TaskFieldInfo taskFieldInfo_4 = new TaskFieldInfo(task_4.getTaskName(), 90, null, null);
+        ServiceResult<Task> result_4 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_4);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.OK, result_4.getExitCode());
         assertEquals(task_4, result_4.getResult());
 
         //Situation 5: deadline and start is updated in a valid way
         Task task_5 = entityManager.find(Task.class, 1L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_5 = new TaskFieldInfo(task_5.getTaskName(), task_5.getEta(), LocalDate.of(2023, 4, 9), LocalDate.of(2023,5,9));
         ServiceResult<Task> result_5 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_5);
         task_5.setStartDate(LocalDate.of(2023,4,9));
         task_5.setDeadline(LocalDate.of(2023,5,9));
+=======
+        task_5.setStartDate(LocalDate.of(2023,4,9));
+        task_5.setDeadline(LocalDate.of(2023,5,9));
+        TaskFieldInfo taskFieldInfo_5 = new TaskFieldInfo(task_5.getTaskName(), task_5.getEta(), LocalDate.of(2023, 4, 9), LocalDate.of(2023,5,9));
+        ServiceResult<Task> result_5 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_5);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.OK, result_5.getExitCode());
         assertEquals(task_5, result_5.getResult());
 
         //Situation 6: Deadline and start are updated in a not valid way
         Task task_6 = entityManager.find(Task.class, 1L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_6 = new TaskFieldInfo(task_5.getTaskName(), task_5.getEta(), LocalDate.of(2023, 5, 9), LocalDate.of(2023,4,9));
         ServiceResult<Task> result_6 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_6);
         task_6.setStartDate(LocalDate.of(2023,5,9));
         task_6.setDeadline(LocalDate.of(2023,4,9));
+=======
+        task_6.setStartDate(LocalDate.of(2023,5,9));
+        task_6.setDeadline(LocalDate.of(2023,4,9));
+        TaskFieldInfo taskFieldInfo_6 = new TaskFieldInfo(task_5.getTaskName(), task_5.getEta(), LocalDate.of(2023, 5, 9), LocalDate.of(2023,4,9));
+        ServiceResult<Task> result_6 = taskService.editTask(entityManager.find(Task.class, 1L), taskFieldInfo_6);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.INVALID_PARAMETER, result_6.getExitCode());
         assertNotEquals(task_6, result_6.getResult());
 
         //Situation 10 Startdate = null;
         Task task_10 = entityManager.find(Task.class, 5L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_10 = new TaskFieldInfo(task_10.getTaskName(), task_10.getEta(),null, task_10.getDeadline());
         ServiceResult<Task> result_10 = taskService.editTask(entityManager.find(Task.class, 5L), taskFieldInfo_10);
         task_10.setStartDate(null);
+=======
+        task_10.setStartDate(null);
+        TaskFieldInfo taskFieldInfo_10 = new TaskFieldInfo(task_10.getTaskName(), task_10.getEta(),null, task_10.getDeadline());
+        ServiceResult<Task> result_10 = taskService.editTask(entityManager.find(Task.class, 5L), taskFieldInfo_10);
+>>>>>>> 5e39cb1 (TaskService Test will fail)
         assertEquals(ServiceExitCode.OK, result_10.getExitCode());
         assertEquals(task_10, result_10.getResult());
 
         //Situation 11 Deadline = null
         Task task_11 = entityManager.find(Task.class, 5L);
+<<<<<<< HEAD
         TaskFieldInfo taskFieldInfo_11 = new TaskFieldInfo(task_11.getTaskName(), task_11.getEta(),task_11.getStartDate(), null);
         ServiceResult<Task> result_11 = taskService.editTask(entityManager.find(Task.class, 5L), taskFieldInfo_11);
         task_11.setDeadline(null);
@@ -177,15 +222,32 @@ public class TaskServiceTest {
         assertEquals(task_11, result_11.getResult());
     }
 
+=======
+        task_11.setDeadline(null);
+        TaskFieldInfo taskFieldInfo_11 = new TaskFieldInfo(task_11.getTaskName(), task_11.getEta(),task_11.getStartDate(), null);
+        ServiceResult<Task> result_11 = taskService.editTask(entityManager.find(Task.class, 5L), taskFieldInfo_11);
+        assertEquals(ServiceExitCode.OK, result_11.getExitCode());
+        assertEquals(task_11, result_11.getResult());
+    }
+>>>>>>> 5e39cb1 (TaskService Test will fail)
     @Test
     @SqlGroup({
             @Sql("classpath:taskgroupRepositoryTestEntries.sql"),
             @Sql("classpath:taskRepositoryEntries.sql")
     })
     void deleteTask() {
+<<<<<<< HEAD
         for(long i=1; i<=15; i++) {
             taskRepository.deleteByTaskID(entityManager.find(Task.class, i).getTaskID());
             assertThat(entityManager.find(Task.class, i)).isNull();
         }
+=======
+        Task task = entityManager.find(Task.class, 1L);
+        task.getTaskgroup().getTasks().remove(task);
+        taskgroupRepository.save(task.getTaskgroup());
+        Task updatedTask = entityManager.find(Task.class, 1L);
+        taskRepository.deleteByTaskID(entityManager.find(Task.class, 1L).getTaskID());
+        assertThat(entityManager.find(Task.class, 1L)).isNull();
+>>>>>>> 5e39cb1 (TaskService Test will fail)
     }
 }