vitest-class-mocking

Vitest hoists vi.mock calls to the top of the file, causing the mocked class to be undefined at mock creation time and resulting in a runtime "is not a constructor" error. Defining the class inline inside the mock factory resolves this hoisting issue.

To mock a class in Vitest without hoisting errors, define the mock class inline directly inside the vi.mock factory function. This ensures the class definition is available when the mock is created, bypassing hoisting-related reference issues.

Yes, you can use vi.hoisted() to create shared class mocks across multiple Vitest tests. This pattern lifts the mock definition outside the vi.mock factory while maintaining proper execution order, ensuring consistent class mocking throughout your test suite.

The best way to mock multiple related classes in Vitest is applying consistent patterns using inline class definitions inside the vi.mock factory. This approach prevents individual hoisting conflicts and maintains reliable constructor behavior across all mocked dependencies.

Yes, Vitest mock hoisting affects TypeScript unit tests by breaking class-based dependencies. When vi.mock attempts to replace a class before its definition is evaluated, the mock returns undefined, causing unit tests requiring new instances to fail at runtime.