What kinds of mocks can it generate?

Four: a function mock (a fake function with a configurable return value), a module mock (a jest.mock or vi.mock factory replacing an import), a class mock (a constructor mock whose methods are stubbed), and an API / fetch mock (a global fetch stub plus an axios mock that resolves a sample response). Choosing a type also changes the input label so you know whether to enter a name, path, or endpoint.

How does the return value and custom implementation work?

Those two controls appear only for the Function mock type. The Return value field is inserted directly into mockReturnValue / returns (it defaults to ’mocked value’ and is treated as a code expression, so quote strings yourself). Enabling "Custom implementation" instead emits a jest.fn or vi.fn with an inline arrow-function body containing a placeholder comment and your return value.

Does Sinon support module mocking here?

Not directly. Sinon has no built-in automatic module mocking, so for the Module type the tool emits a commented note recommending proxyquire or rewire along with an example that stubs a dependency through proxyquire. Jest and Vitest get true jest.mock / vi.mock factory output instead.

What does the API mock include?

The API / Fetch mock scaffolds two approaches: it overrides global.fetch with a stub that resolves an object exposing json(), ok: true, and status: 200, and it also shows how to mock axios so axios.get resolves a sample payload ({ data: { id: 1, name: ’Test’ }, status: 200 }). The Sinon variant uses sinon.stub on global fetch instead.

Is the generated mock ready to drop into a test?

It is a faithful boilerplate for the chosen framework and target, but you will usually adjust details — real return shapes, actual method names on class mocks (which default to method1/method2), and the correct module or endpoint string. The output is downloadable as a TypeScript file so you can paste and adapt it in your test suite.

Mock Function Generator

Generate Jest, Vitest, or Sinon mocks for functions, modules, classes, and APIs

About this ToolHow it works, benefits & use cases

The Mock Function Generator produces test-double boilerplate for Jest, Vitest, or Sinon across four kinds of target: a plain function, an imported module, a class, and an API or fetch call. The form adapts to your choice — the input label and placeholder change to "Function name", "Module path", "Class name", or "API endpoint" as appropriate, and when mocking a function you also get a Return value field and a "Custom implementation" toggle. For functions it emits jest.fn().mockReturnValue(...), a vi.fn() equivalent, or a sinon.stub().returns(...), with an optional inline implementation body. Module mocks generate jest.mock / vi.mock factories (and a proxyquire note for Sinon, which has no built-in module mocking); class mocks return constructor mocks with stubbed methods; and API mocks scaffold a global fetch stub plus an axios mock returning a sample 200 response. One-click example buttons load a representative target for each type. Copy the snippet or download it as a TypeScript file, and the configuration is shareable via URL.

How to Use

1Pick a Test framework (Jest, Vitest, or Sinon) and a Mock type (Function, Module, Class, or API / Fetch).
2For functions, set the Return value and optionally enable "Custom implementation" for an inline body.
3Enter the identifier in the input — a function name, module path, class name, or endpoint — or click an example button to load one.
4Click "Generate Mock" to produce the mock code for your chosen framework and type.
5Copy the snippet into your test file or download it as mock.ts; use Share to pass the configuration along.

Key Benefits

Four mock targets: function, module, class, and API/fetch
Framework-specific output for Jest (jest.fn / jest.mock), Vitest (vi.fn / vi.mock), and Sinon (stub)
Configurable return value and an optional custom-implementation body for function mocks
API mocks scaffold both a global fetch stub and an axios mock with a sample 200 response
Adaptive input label and placeholder that match the selected mock type
Example buttons that switch type and load a representative identifier in one click
Copyable TypeScript output plus a shareable configuration URL

Common Use Cases

Stubbing a helper function to return a fixed value in a unit test
Mocking an imported module so a dependency is isolated from the unit under test
Replacing a service class with stubbed methods for controller or component tests
Faking a fetch or axios API call with a deterministic 200 response
Porting an existing mock between Jest and Vitest syntax

Options

Test framework

Mock type

Return value

Custom implementation

Function name

Enter the identifier to generate a mock for

Generated mock code

Copy into your test file

Run to see the generated mock.

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Mock Function Generator

How to Use

Key Benefits

Common Use Cases

Options

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