unit-test-exception-handler

Unit Testing ExceptionHandler and ControllerAdvice

Overview

This skill provides patterns for writing unit tests for Spring Boot exception handlers. It covers testing @ExceptionHandler methods in @ControllerAdvice classes using MockMvc, including HTTP status assertions, JSON response validation, field-level validation error testing, and mocking handler dependencies.

When to Use

• Writing unit tests for @ExceptionHandler methods
• Testing @ControllerAdvice global exception handling
• Validating REST API error response formatting
• Mocking exceptions in controller tests
• Testing field-level validation error responses
• Asserting custom error payloads and HTTP status codes

Instructions

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

Examples

Exception Handler and Error DTO