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Mocks

Learn how to create and use mock functions, spies, and module mocks in Bun tests

Lifecycle hooks

Learn how to use beforeAll, beforeEach, afterEach, and afterAll lifecycle hooks in Bun tests

Snapshots

Learn how to use snapshot testing in Bun to save and compare output between test runs

On this page

Basic Function Mocks Jest Compatibility Mock Function Properties Available Properties and Methods Practical Examples Basic Mock Usage Dynamic Mock Implementations Async Mocks Spies with spyOn()Advanced Spy Usage Module Mocks with mock.module()Overriding Already Imported Modules Hoisting & Preloading Module Mock Best Practices When to Use Preload Practical Module Mock Examples Mocking External Dependencies Global Mock Functions Clear All Mocks Reset All Mocks Restore All Mocks Vitest Compatibility Implementation Details Cache Interaction Lazy Evaluation Path Resolution Import Timing Effects Live Bindings Advanced Patterns Factory Functions Conditional Mocking Mock Cleanup Patterns Best Practices Keep Mocks Simple Use Type-Safe Mocks Test Mock Behavior Notes Auto-mocking ESM vs CommonJS