jest/prefer-mock-promise-shorthand Style

🛠️ An auto-fix is available for this rule for some violations.

What it does

When working with mocks of functions that return promises, Jest provides some API sugar functions to reduce the amount of boilerplate you have to write. These methods should be preferred when possible.

Why is this bad?

Using generic mock functions like mockImplementation(() => Promise.resolve()) or mockReturnValue(Promise.reject()) is more verbose and less readable than Jest's specialized promise shorthands. The shorthand methods like mockResolvedValue() and mockRejectedValue() are more expressive and make the test intent clearer.

Examples

Examples of incorrect code for this rule:

jest.fn().mockImplementation(() => Promise.resolve(123));
jest
  .spyOn(fs.promises, "readFile")
  .mockReturnValue(Promise.reject(new Error("oh noes!")));

myFunction
  .mockReturnValueOnce(Promise.resolve(42))
  .mockImplementationOnce(() => Promise.resolve(42))
  .mockReturnValue(Promise.reject(new Error("too many calls!")));

Examples of correct code for this rule:

jest.fn().mockResolvedValue(123);
jest.spyOn(fs.promises, "readFile").mockRejectedValue(new Error("oh noes!"));

myFunction
  .mockResolvedValueOnce(42)
  .mockResolvedValueOnce(42)
  .mockRejectedValue(new Error("too many calls!"));

How to use

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

CLI

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

Config (.oxlintrc.json)

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

References

• Rule Source