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error-testing.md

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name Vitest Error Testing
description A guide to testing error conditions, exception handling, and failure scenarios to ensure robust error handling in applications.
tier technology
schema procedure
tags
testing
vitest
errors
exceptions
layer

Primary Directive

You MUST thoroughly test error conditions and exception handling to verify that your application behaves correctly under failure scenarios and provides appropriate error responses.

Process

  1. Identify Error Scenarios: Catalog all possible error conditions including invalid inputs, network failures, authorization errors, and resource unavailability that your code should handle.

  2. Test Synchronous Errors: Use expect().toThrow() to verify that functions throw expected errors with specific error types, messages, and properties for synchronous error conditions.

  3. Test Asynchronous Errors: Use expect().rejects.toThrow() or expect().rejects.toEqual() to test promise rejections and async function errors with proper error type and message validation.

  4. Verify Error Messages: Assert that error messages are meaningful, consistent, and provide sufficient information for debugging while avoiding exposure of sensitive system details.

  5. Test Error Boundaries: Verify that error handling mechanisms (try-catch blocks, error boundaries, middleware) properly catch and process errors without causing application crashes.

  6. Mock Error Conditions: Use vi.mock() and vi.fn().mockRejectedValue() to simulate external service failures, network timeouts, and other error conditions that are difficult to reproduce naturally.

  7. Test Error Recovery: Verify that applications properly recover from errors, clean up resources, reset state, and continue functioning after error conditions are resolved.

  8. Validate Error Logging: Ensure that errors are properly logged with appropriate severity levels and structured data for monitoring and debugging purposes.

Constraints

  • You MUST test both the error throwing behavior and the error handling behavior to ensure complete error flow coverage.
  • You MUST NOT rely on production errors for testing; always use controlled error simulation through mocks and deliberate invalid inputs.
  • You MUST verify that error handling does not introduce memory leaks, resource leaks, or corrupted application state.
  • You MUST test error conditions at appropriate boundaries including input validation, external service calls, and internal component interfaces.
  • You MUST ensure that error tests are deterministic and do not depend on external factors or timing for consistent execution.