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jest/prefer-mock-return-shorthand Style

🛠️ An auto-fix is available for this rule.

What it does

When working with mocks of functions that return simple values, Jest provides some API sugar functions to reduce the amount of boilerplate you have to write.

Why is this bad?

Not using Jest’s API sugar functions adds unnecessary boilerplate and makes tests harder to read. These helpers clearly express intent and reduce errors, keeping tests simple and maintainable.

Examples

Examples of incorrect code for this rule:

jest.fn().mockImplementation(() => "hello world");

jest
  .spyOn(fs.promises, "readFile")
  .mockImplementationOnce(() => Promise.reject(new Error("oh noes!")));

myFunction
  .mockImplementationOnce(() => 42)
  .mockImplementationOnce(() => Promise.resolve(42))
  .mockReturnValue(0);

Examples of correct code for this rule:

jest.fn().mockResolvedValue(123);

jest.spyOn(fs.promises, "readFile").mockReturnValue(Promise.reject(new Error("oh noes!")));
jest.spyOn(fs.promises, "readFile").mockRejectedValue(new Error("oh noes!"));

jest.spyOn(fs, "readFileSync").mockImplementationOnce(() => {
  throw new Error("oh noes!");
});

myFunction.mockResolvedValueOnce(42).mockResolvedValueOnce(42).mockReturnValue(0);

This rule is compatible with eslint-plugin-vitest, to use it, add the following configuration to your .oxlintrc.json:

{
  "rules": {
    "vitest/prefer-mock-return-shorthand": "error"
  }
}

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "plugins": ["jest"],
  "rules": {
    "jest/prefer-mock-return-shorthand": "error"
  }
}

CLI

oxlint --deny jest/prefer-mock-return-shorthand --jest-plugin

References

• Rule Source