I want to create a custom matcher in Jest. I would expect that this should go in my jest-setup.js file, specified in my jest.config.js file.

jest-setup.js

// ...

expect.extend({
    myCustomMatcher(received, val) {
        // ...
    }
});

Unfortunately, while jest is a global variable at this point in the execution, it appears that expect is not. I can put my extension in a helper file and import that file for any test suite that uses it, but that seems like the wrong solution.

Is there a way to access expect from the jest variable (or some other means)?

I want to create a custom matcher in Jest. I would expect that this should go in my jest-setup.js file, specified in my jest.config.js file.

jest-setup.js

// ...

expect.extend({
    myCustomMatcher(received, val) {
        // ...
    }
});

Unfortunately, while jest is a global variable at this point in the execution, it appears that expect is not. I can put my extension in a helper file and import that file for any test suite that uses it, but that seems like the wrong solution.

Is there a way to access expect from the jest variable (or some other means)?

• javascript
• jestjs

1 Answer 1

You can use setupFilesAfterEnv to do that. From the docs (emphasis mine):

setupFilesAfterEnv [array]

A list of paths to modules that run some code to configure or set up the testing framework before each test. Since setupFiles executes before the test framework is installed in the environment, this script file presents you the opportunity of running some code immediately after the test framework has been installed in the environment.