test: add coverage for race condition and null ID edge cases (#248)

- Add test for DataIntegrityViolationException during concurrent creates
- Add test for PUT with null body ID (validates ID from path)
- Refactor URI construction to use ServletUriComponentsBuilder

Author: nanotaboada

src/main/java/ar/com/nanotaboada/java/samples/spring/boot/controllers/PlayersController.java

@@ -14,7 +14,7 @@
 import org.springframework.web.bind.annotation.PutMapping;
 import org.springframework.web.bind.annotation.RequestBody;
 import org.springframework.web.bind.annotation.RestController;
-import org.springframework.web.servlet.mvc.method.annotation.MvcUriComponentsBuilder;
+import org.springframework.web.servlet.support.ServletUriComponentsBuilder;
 
 import ar.com.nanotaboada.java.samples.spring.boot.models.PlayerDTO;
 import ar.com.nanotaboada.java.samples.spring.boot.services.PlayersService;
@@ -97,9 +97,10 @@ public ResponseEntity<Void> post(@RequestBody @Valid PlayerDTO playerDTO) {
         if (createdPlayer == null) {
             return ResponseEntity.status(HttpStatus.CONFLICT).build();
         }
-        URI location = MvcUriComponentsBuilder
-                .fromMethodCall(MvcUriComponentsBuilder.on(PlayersController.class).getById(createdPlayer.getId()))
-                .build()
+        URI location = ServletUriComponentsBuilder
+                .fromCurrentRequest()
+                .path("/{id}")
+                .buildAndExpand(createdPlayer.getId())
                 .toUri();
         return ResponseEntity.status(HttpStatus.CREATED)
                 .header(LOCATION, location.toString())

src/test/java/ar/com/nanotaboada/java/samples/spring/boot/test/controllers/PlayersControllerTests.java

@@ -482,6 +482,36 @@ void put_idMismatch_returnsBadRequest()
         assertThat(response.getStatus()).isEqualTo(HttpStatus.BAD_REQUEST.value());
     }
 
+    /**
+     * Given the body ID is null (ID only in path)
+     * When PUT /players/{id} is called
+     * Then the ID is set from the path and the update proceeds normally
+     */
+    @Test
+    void put_nullBodyId_setsIdFromPath()
+            throws Exception {
+        // Arrange
+        PlayerDTO playerDTO = PlayerDTOFakes.createOneValid();
+        playerDTO.setId(null); // Body has null ID
+        Long pathId = 1L;
+        String body = objectMapper.writeValueAsString(playerDTO);
+        Mockito
+                .when(playersServiceMock.update(any(PlayerDTO.class)))
+                .thenReturn(true);
+        MockHttpServletRequestBuilder request = MockMvcRequestBuilders
+                .put(PATH + "/{id}", pathId)
+                .content(body)
+                .contentType(MediaType.APPLICATION_JSON);
+        // Act
+        MockHttpServletResponse response = application
+                .perform(request)
+                .andReturn()
+                .getResponse();
+        // Assert
+        verify(playersServiceMock, times(1)).update(any(PlayerDTO.class));
+        assertThat(response.getStatus()).isEqualTo(HttpStatus.NO_CONTENT.value());
+    }
+
     /*
      * -------------------------------------------------------------------------
      * HTTP DELETE

src/test/java/ar/com/nanotaboada/java/samples/spring/boot/test/services/PlayersServiceTests.java

@@ -25,6 +25,7 @@
 import ar.com.nanotaboada.java.samples.spring.boot.services.PlayersService;
 import ar.com.nanotaboada.java.samples.spring.boot.test.PlayerDTOFakes;
 import ar.com.nanotaboada.java.samples.spring.boot.test.PlayerFakes;
+import org.springframework.dao.DataIntegrityViolationException;
 
 @DisplayName("CRUD Operations on Service")
 @ExtendWith(MockitoExtension.class)
@@ -98,6 +99,33 @@ void create_squadNumberExists_returnsNull() {
         assertThat(result).isNull();
     }
 
+    /**
+     * Given a race condition occurs where another request creates the same squad number
+     * When create() is called and save() throws DataIntegrityViolationException
+     * Then null is returned (conflict detected via exception)
+     */
+    @Test
+    void create_raceConditionOnSave_returnsNull() {
+        // Arrange
+        PlayerDTO playerDTO = PlayerDTOFakes.createOneValid();
+        Player player = PlayerFakes.createOneValid();
+        Mockito
+                .when(playersRepositoryMock.findBySquadNumber(playerDTO.getSquadNumber()))
+                .thenReturn(Optional.empty()); // No conflict initially
+        Mockito
+                .when(modelMapperMock.map(playerDTO, Player.class))
+                .thenReturn(player);
+        Mockito
+                .when(playersRepositoryMock.save(any(Player.class)))
+                .thenThrow(new DataIntegrityViolationException("Unique constraint violation"));
+        // Act
+        PlayerDTO result = playersService.create(playerDTO);
+        // Assert
+        verify(playersRepositoryMock, times(1)).findBySquadNumber(playerDTO.getSquadNumber());
+        verify(playersRepositoryMock, times(1)).save(any(Player.class));
+        assertThat(result).isNull();
+    }
+
     /*
      * -----------------------------------------------------------------------------------------------------------------------
      * Retrieve