test: add jsonPath field assertions to create validation tests

src/test/java/de/zendric/app/xpensely_Server/controller/ExpenseListControllerTest.java

@@ -155,7 +155,8 @@ class ExpenseListControllerTest {
         mockMvc.perform(post("/api/expenselist/create")
                         .contentType(MediaType.APPLICATION_JSON)
                         .content("{\"name\":\"\"}"))
-                .andExpect(status().isBadRequest());
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.name").exists());
     }
 
     @Test
@@ -167,6 +168,7 @@ class ExpenseListControllerTest {
         mockMvc.perform(post("/api/expenselist/create")
                         .contentType(MediaType.APPLICATION_JSON)
                         .content("{}"))
-                .andExpect(status().isBadRequest());
+                .andExpect(status().isBadRequest())
+                .andExpect(jsonPath("$.name").exists());
     }
 }