vitest-best-practices-auto

Vitest Unit Testing Best Practices

This rule enforces and suggests best practices when writing Vitest unit tests to ensure reliable, maintainable, and expressive test suites.

Critical Rules

• Tests must use clear and descriptive names (it/test strings).
• Use "Arrange, Act, Assert" pattern for writing unit tests.
• Use describe blocks to group related tests logically.
• Use beforeEach/afterEach for shared setup/teardown instead of duplicating code.
• Cleanup side-effects using vi.resetAllMocks() or vi.restoreAllMocks().
• Prefer vi.fn() or vi.spyOn() over manually created stubs.
• Avoid global state – never rely on test execution order.
• For asynchronous code, always await promises and/or use expect.assertions(n).
• Do not snapshot complex objects blindly; snapshot only stable, meaningful output.
• Use vi.useFakeTimers() cautiously and always restore real timers with vi.useRealTimers() afterwards.
• Do not disable tests with test.skip/it.skip; instead, fix or remove them.
• Keep test files co-located with source or in a dedicated __tests__ folder.
• Ensure each test has at least one expect call (or uses .resolves/.rejects).
• Prefer explicit assertions over implicit truthiness checks.

filters:

Match Vitest test files

• type: file_extension pattern: "\.(test|spec)\.(js|ts|jsx|tsx)$"

Warn if test title is non-descriptive (too short)

• type: content pattern: "\b(?:it|test)\((?:'|")\s*[A-Za-z0-9]{1,10}\s*(?:'|")"

Prevent skipped tests

• type: content pattern: "\b(?:it|test|describe)\.skip\("

Ensure at least one expect‡ per test block (heuristic)

• type: content pattern: "\b(?:it|test)\([^)]{(?:(?!expect).)}$"

actions:

Suggest more descriptive titles

• type: suggest message: | Test titles should be descriptive. Use behaviour-driven phrases, e.g. it('renders submit button when form is valid', ...).