diff --git a/src/main/java/de/szut/lf8_starter/project/action/crud/CreateProjectAction.java b/src/main/java/de/szut/lf8_starter/project/action/crud/CreateProjectAction.java
index 6b0c3b5..8319011 100644
--- a/src/main/java/de/szut/lf8_starter/project/action/crud/CreateProjectAction.java
+++ b/src/main/java/de/szut/lf8_starter/project/action/crud/CreateProjectAction.java
@@ -46,7 +46,7 @@ public class CreateProjectAction {
 
         for (Long employeeId : createProjectDto.getEmployees()) {
             if (!this.employeeService.employeeExists(accessToken, employeeId)) {
-                return new ResponseEntity<>(HttpStatus.NOT_FOUND);
+                return new ResponseEntity<>("Employee with ID: " + employeeId + " not found", HttpStatus.NOT_FOUND);
             }
 
             for (GetProjectDto getProjectDto : this.employeeService.getProjects(employeeId)) {
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/AddEmployeeToProjectTest.java b/src/test/java/de/szut/lf8_starter/integration/project/AddEmployeeToProjectTest.java
index 4193e77..3efc563 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/AddEmployeeToProjectTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/AddEmployeeToProjectTest.java
@@ -7,6 +7,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.*;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -22,7 +23,8 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
-class AddEmployeeToProjectActionIntegrationTest {
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
+class AddEmployeeToProjectTest {
     @Autowired
     private MockMvc mockMvc;
 
@@ -56,6 +58,87 @@ class AddEmployeeToProjectActionIntegrationTest {
         assert updatedProject.getEmployees().contains(312L);
     }
 
+    @Test
+    void addEmployeeToPastProjectTest() throws Exception {
+        ProjectEntity project = new ProjectEntity();
+        project.setComment("past project");
+        project.setContractor(1);
+        project.setContractorName("contractorName");
+        project.setPlannedEndDate(LocalDate.of(1991, 1, 1));
+        project.setLeadingEmployee(1);
+        project.setName("past project");
+        project.setStartDate(LocalDate.of(1990, 1, 1));
+        project.setEmployees(List.of(1L, 2L, 3L));
+        this.projectRepository.save(project);
+
+        mockMvc.perform(post("/projects/{projectId}/employees/{employeeId}", project.getId(), 312)
+                        .header(HttpHeaders.AUTHORIZATION, getBearerToken())
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isNoContent());
+
+        ProjectEntity updatedProject = projectRepository.findById(project.getId()).get();
+
+        assert updatedProject.getEmployees().contains(312L);
+    }
+
+    @Test
+    void addEmployeeToFutureProjectTest() throws Exception {
+        ProjectEntity project = new ProjectEntity();
+        project.setComment("future project");
+        project.setContractor(1);
+        project.setContractorName("contractorName");
+        project.setPlannedEndDate(LocalDate.of(2101, 1, 1));
+        project.setLeadingEmployee(1);
+        project.setName("future project");
+        project.setStartDate(LocalDate.of(2100, 1, 1));
+        project.setEmployees(List.of(1L, 2L, 3L));
+        this.projectRepository.save(project);
+
+        mockMvc.perform(post("/projects/{projectId}/employees/{employeeId}", project.getId(), 312)
+                        .header(HttpHeaders.AUTHORIZATION, getBearerToken())
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isNoContent());
+
+        ProjectEntity updatedProject = projectRepository.findById(project.getId()).get();
+
+        assert updatedProject.getEmployees().contains(312L);
+    }
+
+    @Test
+    void addEmployeeToProjectWithOverlappingDatesTest() throws Exception {
+        ProjectEntity project1 = new ProjectEntity();
+        project1.setComment("project 1");
+        project1.setContractor(1);
+        project1.setContractorName("contractorName");
+        project1.setPlannedEndDate(LocalDate.of(2023, 1, 1));
+        project1.setLeadingEmployee(1);
+        project1.setName("project 1");
+        project1.setStartDate(LocalDate.of(2022, 1, 1));
+        project1.setEmployees(List.of(1L, 2L, 3L));
+        this.projectRepository.save(project1);
+
+        ProjectEntity project2 = new ProjectEntity();
+        project2.setComment("project 2");
+        project2.setContractor(1);
+        project2.setContractorName("contractorName");
+        project2.setPlannedEndDate(LocalDate.of(2023, 6, 1));
+        project2.setLeadingEmployee(1);
+        project2.setName("project 2");
+        project2.setStartDate(LocalDate.of(2022, 6, 1));
+        project2.setEmployees(List.of(1L, 2L, 3L));
+        this.projectRepository.save(project2);
+
+        mockMvc.perform(post("/projects/{projectId}/employees/{employeeId}", project1.getId(), 312)
+                        .header(HttpHeaders.AUTHORIZATION, getBearerToken())
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isNoContent());
+
+        mockMvc.perform(post("/projects/{projectId}/employees/{employeeId}", project2.getId(), 312)
+                        .header(HttpHeaders.AUTHORIZATION, getBearerToken())
+                        .contentType(MediaType.APPLICATION_JSON))
+                .andExpect(status().isConflict());
+    }
+
     private String getBearerToken() {
         String url = "https://keycloak.szut.dev/auth/realms/szut/protocol/openid-connect/token";
 
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/CreateProjectActionTest.java b/src/test/java/de/szut/lf8_starter/integration/project/CreateProjectActionTest.java
index c5f87cc..881b71a 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/CreateProjectActionTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/CreateProjectActionTest.java
@@ -3,12 +3,12 @@ package de.szut.lf8_starter.integration.project;
 import de.szut.lf8_starter.project.ProjectEntity;
 import de.szut.lf8_starter.project.ProjectRepository;
 import org.json.JSONObject;
-import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.*;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -28,6 +28,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class CreateProjectActionTest {
     @Autowired
     private MockMvc mockMvc;
@@ -36,11 +37,6 @@ class CreateProjectActionTest {
     @Autowired
     private RestTemplate restTemplate;
 
-    @BeforeEach
-    public void clear() {
-        this.projectRepository.deleteAll();
-    }
-
     @Test
     void createProjectTest() throws Exception {
         String content = """
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/GetEmployeesFromProjectTest.java b/src/test/java/de/szut/lf8_starter/integration/project/GetEmployeesFromProjectTest.java
index 985fd2f..8b73e06 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/GetEmployeesFromProjectTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/GetEmployeesFromProjectTest.java
@@ -7,6 +7,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.*;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -23,6 +24,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class GetEmployeesFromProjectTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/GetProjectActionTest.java b/src/test/java/de/szut/lf8_starter/integration/project/GetProjectActionTest.java
index 1b6ed3f..c3d2235 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/GetProjectActionTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/GetProjectActionTest.java
@@ -6,6 +6,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 
 import java.time.LocalDate;
@@ -18,6 +19,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class GetProjectActionTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/GetProjectsFromEmployeeTest.java b/src/test/java/de/szut/lf8_starter/integration/project/GetProjectsFromEmployeeTest.java
index 769bd69..f7282ee 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/GetProjectsFromEmployeeTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/GetProjectsFromEmployeeTest.java
@@ -7,6 +7,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.*;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -23,6 +24,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class GetProjectsFromEmployeeTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllNotAuthenticated.java b/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllNotAuthenticated.java
deleted file mode 100644
index bda3c51..0000000
--- a/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllNotAuthenticated.java
+++ /dev/null
@@ -1,32 +0,0 @@
-package de.szut.lf8_starter.integration.project;
-
-import de.szut.lf8_starter.project.ProjectRepository;
-import org.junit.jupiter.api.Test;
-import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
-import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.boot.test.web.client.TestRestTemplate;
-import org.springframework.test.web.servlet.MockMvc;
-
-
-import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
-import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
-
-@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
-@AutoConfigureMockMvc(addFilters = true)
-class ProjectFindAllNotAuthenticated {
-    @Autowired
-    private ProjectRepository projectRepository;
-
-    @Autowired
-    private MockMvc mockMvc;
-
-    @Autowired
-    private TestRestTemplate restTemplate;
-
-    @Test
-    void findAllProjects() throws Exception {
-        this.mockMvc.perform(get("/projects"))
-                .andExpect(status().isUnauthorized());
-    }
-}
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllSuccessTest.java b/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllSuccessTest.java
index ff3a642..e424a92 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllSuccessTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/ProjectFindAllSuccessTest.java
@@ -6,6 +6,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 
 import java.time.LocalDate;
@@ -18,6 +19,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class ProjectFindAllSuccessTest {
     @Autowired
     private ProjectRepository projectRepository;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/RemoveEmployeeFromProjectIntegrationTest.java b/src/test/java/de/szut/lf8_starter/integration/project/RemoveEmployeeFromProjectIntegrationTest.java
index 7e55dd8..4008ddb 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/RemoveEmployeeFromProjectIntegrationTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/RemoveEmployeeFromProjectIntegrationTest.java
@@ -7,6 +7,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.*;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
@@ -17,11 +18,12 @@ import java.util.List;
 import java.util.Map;
 import java.util.Objects;
 
-import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
+import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.delete;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class RemoveEmployeeFromProjectIntegrationTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/RemoveProjectActionTest.java b/src/test/java/de/szut/lf8_starter/integration/project/RemoveProjectActionTest.java
index c2c47dd..0dd94fe 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/RemoveProjectActionTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/RemoveProjectActionTest.java
@@ -6,6 +6,7 @@ import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 
 import java.time.LocalDate;
@@ -17,6 +18,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class RemoveProjectActionTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/java/de/szut/lf8_starter/integration/project/UpdateProjectActionTest.java b/src/test/java/de/szut/lf8_starter/integration/project/UpdateProjectActionTest.java
index a38e233..74d889b 100644
--- a/src/test/java/de/szut/lf8_starter/integration/project/UpdateProjectActionTest.java
+++ b/src/test/java/de/szut/lf8_starter/integration/project/UpdateProjectActionTest.java
@@ -8,6 +8,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.autoconfigure.web.servlet.AutoConfigureMockMvc;
 import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.MediaType;
+import org.springframework.test.annotation.DirtiesContext;
 import org.springframework.test.web.servlet.MockMvc;
 
 import java.time.LocalDate;
@@ -23,6 +24,7 @@ import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.
 
 @SpringBootTest
 @AutoConfigureMockMvc(addFilters = false)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
 class UpdateProjectActionTest {
     @Autowired
     private MockMvc mockMvc;
diff --git a/src/test/resources/application-test.properties b/src/test/resources/application-test.properties
new file mode 100644
index 0000000..f45162f
--- /dev/null
+++ b/src/test/resources/application-test.properties
@@ -0,0 +1,6 @@
+spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1;DB_CLOSE_ON_EXIT=FALSE
+spring.datasource.driverClassName=org.h2.Driver
+spring.datasource.username=sa
+spring.datasource.password=password
+spring.jpa.database-platform=org.hibernate.dialect.H2Dialect
+spring.jpa.hibernate.ddl-auto=create-drop
\ No newline at end of file