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Mock a child component with an inline factory
Use jest.mock with the same module path the parent uses. The factory below supplies a valid, deliberately simple React component in place of ./Child:
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jest.mock('./Child', () => () => <mock-child />);This JSX form requires a test transform that supports JSX. If yours does not, return an element created with React.createElement instead:
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jest.mock('./Child', () => () => React.createElement('mock-child'));Keep the placeholder focused on what the parent test needs. If the parent passes children or props that affect its behavior, the mock can render or use those values. Avoid returning the string 'Child' as a component type: Jest’s React tutorial warns that uppercase string tags can produce React warnings in snapshot tests. A lowercase custom element or simple text is a safer placeholder. Jest’s React testing tutorial shows DOM-based testing and discusses this mock-rendering caveat.
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Test the parent’s behavior, not the child’s implementation
A child mock is useful when the parent test needs to isolate complex rendering or third-party behavior. It does not prove that the real child works. Keep assertions centered on what a user can see or do, such as parent-rendered text, an enabled state, or the result of an interaction. Jest’s React tutorial demonstrates rendering with @testing-library/react and making interaction assertions; it does not require mocking every child.
If the parent responds to a callback passed to its child, a behavior-bearing stub can expose a button that calls that callback. The test can then verify the parent’s response without recreating the child’s full implementation:
jest.mock('./Child', () => ({ onSave }) => (
<button onClick={onSave}>Save</button>
));Use this only when invoking that callback is part of the parent behavior being tested. Render the real child when the test’s purpose is to establish how parent and child work together.
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| Situation | Pattern | What to watch |
|---|---|---|
| One test file needs a purpose-built substitute | Inline jest.mock('./Child', factory) |
Use the exact module path and a valid React render result. |
| Several tests need the same stable substitute | A manual mock in a sibling __mocks__ directory |
For a user module, select it explicitly with jest.mock('./moduleName'). The folder name is case-sensitive. |
| The project uses native ESM | jest.unstable_mockModule, followed by dynamic imports |
Static imports run before test code; the API is explicitly unstable. |
Jest’s manual mocks guide explains module-level mocks, manual mock selection, and their scope. A manually maintained mock can drift from the real module; when appropriate, you can extend an automatic mock with jest.createMockFromModule.
Account for export shape and mock scope
For CommonJS modules or imports handled by a transform with Jest mock hoisting, jest.mock is generally registered before imports are evaluated. Keep the mock registration in the same test file and scope as the import or require that consumes the mock, and make the mock path match the path used by the parent. A mock declared in one test file does not automatically affect another test file.
If the mocked module has a default export and your factory returns an object, Jest’s factory conventions may require an object with __esModule: true and a default property. Match the real module’s export shape rather than adding these fields automatically:
jest.mock('./Child', () => ({
__esModule: true,
default: () => <mock-child />,
}));Jest documents the factory and module-mocking mechanics in its manual mocks guide.
Mock native ESM modules with dynamic imports
Do not rely on CommonJS-style jest.mock hoisting above static ESM imports. Static imports are evaluated before the test body, so register the ESM mock first and dynamically import both the dependency and the module under test afterward. The documented API is named jest.unstable_mockModule, and its unstable status is important: confirm that it fits your Jest and Node setup.
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import { jest } from '@jest/globals';
jest.unstable_mockModule('./Child.js', () => ({
default: () => React.createElement('mock-child'),
}));
const { default: Parent } = await import('./Parent.js');This example assumes the parent imports ./Child.js as a default export and that React is available in the test. Adapt the path and returned export to the module under test. See Jest’s ECMAScript modules documentation for the ESM registration and loading requirements; behavior can also depend on the Node version and whether the module graph can be evaluated synchronously.
Update old mock-generation examples for Jest 30
If an older example uses jest.genMockFromModule, replace it with jest.createMockFromModule. Jest 30 removed the former API in favor of the latter, as stated in the Jest 30 upgrade guide. The current Jest documentation identifies its manual mock, mock function, and ESM guides as version 30.5; check the documentation and behavior for the Jest version installed in your project.
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