OZG-4717 Refactored TestConstraintViolationException

src/test/java/de/ozgcloud/admin/common/errorhandling/ExceptionControllerITCase.java

 package de.ozgcloud.admin.common.errorhandling;
 
-import static org.assertj.core.api.Assertions.*;
 import static org.mockito.ArgumentMatchers.*;
 import static org.mockito.Mockito.*;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.*;
@@ -80,14 +79,14 @@ class ExceptionControllerITCase {
 	class TestConstraintViolationException {
 		@Test
 		@SneakyThrows
-		void shouldHaveInfoInBody() {
+		void shouldHaveValidationMessage() {
 			when(modelAssembler.toModel(any())).thenAnswer((a) -> {
 				throw new ConstraintViolationException(getConstraintViolations());
 			});
 
 			var result = performGet();
 
-			assertThat(result.andReturn().getResponse().getContentAsString()).contains("string: Empty field");
+			result.andExpect(jsonPath("$.detail").value("string: Empty field"));
 		}
 
 		private Set<ConstraintViolation<ValidatedClass>> getConstraintViolations() {