Unit Test Exception Handler

What it does

When your agent uses it

• Writing Spring exception handler tests
• REST API error tests
• Mocking controller advice

Example prompts

• “Use the unit-test-exception-handler skill to provide patterns for unit testing @ExceptionHandler and @ControllerAdvice in Spring Boot applications”
• “/unit-test-exception-handler”

Requirements

• Pre-approved tools (allowed-tools): Read, Write, Bash, Glob, Grep

Workflow steps

6 steps, taken from the first numbered list in SKILL.md.

1. 1Create a test controller that throws specific exceptions to trigger each @ExceptionHandler
2. 2Register ControllerAdvice via setControllerAdvice() on MockMvcBuilders.standaloneSetup()
3. 3Assert HTTP status codes with .andExpect(status().isXxx())
4. 4Verify error response fields using jsonPath("$.field") matchers
5. 5Test validation errors by sending invalid payloads and checking MethodArgumentNotValidException produces field-level details
6. 6Debug failures with .andDo(print()) — if handler not invoked, verify setControllerAdvice() is called and exception type matches

What it can do on your machine

Read from SKILL.md and the folder at commit fe73fb3. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves these tools, so the agent can use them without asking each time:

  • Read
  • Write
  • Bash
  • Glob
  • Grep

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are java).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Unit Test Exception Handler loads about 1.6k tokens when it runs, and up to ~2.4k if it reads all its reference files. Until then it costs about 98 tokens; SKILL.md has 369 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~98

When it runs · the whole SKILL.md, loaded when a task matches

~1.6k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~2.4k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NotePre-approves every shell command (allowed-tools: Bash)SKILL.md

  allowed-tools: Read, Write, Bash, Glob, Grep

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from giuseppe-trisciuoglio/developer-kit at commit fe73fb3, republished under its MIT licence (© giuseppe-trisciuoglio). 369 words, ~1,571 tokens.

name

unit-test-exception-handler

description

Provides patterns for unit testing `@ExceptionHandler` and `@ControllerAdvice` in Spring Boot applications. Validates error response formatting, mocks exceptions, verifies HTTP status codes, tests field-level validation errors, and asserts custom error payloads. Use when writing Spring exception handler tests, REST API error tests, or mocking controller advice.

allowed-tools

Read, Write, Bash, Glob, Grep

@ControllerAdvice
public class GlobalExceptionHandler {

  @ExceptionHandler(ResourceNotFoundException.class)
  @ResponseStatus(HttpStatus.NOT_FOUND)
  public ErrorResponse handleNotFound(ResourceNotFoundException ex) {
    return new ErrorResponse(404, "Not Found", ex.getMessage());
  }

  @ExceptionHandler(ValidationException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  public ErrorResponse handleValidation(ValidationException ex) {
    return new ErrorResponse(400, "Bad Request", ex.getMessage());
  }

  @ExceptionHandler(MethodArgumentNotValidException.class)
  @ResponseStatus(HttpStatus.BAD_REQUEST)
  public ValidationErrorResponse handleMethodArgumentNotValid(MethodArgumentNotValidException ex) {
    Map<String, String> errors = new HashMap<>();
    ex.getBindingResult().getFieldErrors().forEach(e -> errors.put(e.getField(), e.getDefaultMessage()));
    return new ValidationErrorResponse(400, "Validation Failed", errors);
  }
}

public record ErrorResponse(int status, String error, String message) {}
public record ValidationErrorResponse(int status, String error, Map<String, String> errors) {}

@ExtendWith(MockitoExtension.class)
class GlobalExceptionHandlerTest {

  private MockMvc mockMvc;

  @BeforeEach
  void setUp() {
    GlobalExceptionHandler handler = new GlobalExceptionHandler();
    mockMvc = MockMvcBuilders.standaloneSetup(new TestController())
        .setControllerAdvice(handler)
        .build();
  }

  @Test
  void shouldReturn404WhenResourceNotFound() throws Exception {
    mockMvc.perform(get("/api/users/999"))
        .andExpect(status().isNotFound())
        .andExpect(jsonPath("$.status").value(404))
        .andExpect(jsonPath("$.error").value("Not Found"))
        .andExpect(jsonPath("$.message").value("User not found"));
  }

  @Test
  void shouldReturn400WithFieldErrorsOnValidationFailure() throws Exception {
    mockMvc.perform(post("/api/users")
        .contentType("application/json")
        .content("{\"name\":\"\",\"email\":\"invalid\"}"))
        .andExpect(status().isBadRequest())
        .andExpect(jsonPath("$.status").value(400))
        .andExpect(jsonPath("$.errors.name").value("must not be blank"))
        .andExpect(jsonPath("$.errors.email").value("must be a valid email"));
  }
}

@RestController
@RequestMapping("/api")
class TestController {
  @GetMapping("/users/{id}") public User getUser(@PathVariable Long id) {
    throw new ResourceNotFoundException("User not found");
  }
  @PostMapping("/users") public User createUser(@RequestBody @Valid User user) {
    throw new ValidationException("Validation failed");
  }
}

© giuseppe-trisciuoglio, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 1 other file (references) in plugins/developer-kit-java/skills/unit-test-exception-handler of giuseppe-trisciuoglio/developer-kit.

• SKILL.md
• references/examples.md

Open the folder on GitHubat commit fe73fb3