This project aims to provide full support for Immutable.js objects within the default Jest matchers. It works by overwriting the equals method to support value objects.

This addition is required since two Immutable.js objects containing the same properties might not always have the same reference. The following example will explain this:

const directlyCreated = new Immutable.Map([['foo', 'bar']]);
const indirectlyCreated = (new Immutable.Map()).set('foo', 'bar');

Immutable.is(directlyCreated, indirectlyCreated); // => true
directlyCreated === indirectlyCreated; // => false

This already works with some of the default matchers like toEqual(), toContain, and toContainEqual since it uses iterators to compare the values. We extend the support for Immutable.js equality checks to all other matchers.

Current support

• Spy Matchers
  • lastCalledWith
  • toBeCalledWith
  • toHaveBeenCalledWith
  • toHaveBeenLastCalledWith

Future plans

To further improve the experience when working with Jest and Immutable.js, we are working on additional matchers as well including:

• toMatchObject
• toHaveProperty
• Asymmetric Matchers
  • immutableMapContaining
  • immutableSetContaining
  • immutableRecordContaining
  • immutableListContaining

Installation

Since this package overwrites Jest's default matchers, you need to invoke it after your setupFiles.

This can be done either in the individual test files, like this:

// some-test.js
import "called-with-immutable";

it("works", () => {
  expect(jest.fn()).not.toBeCalledWith(someImmutableObject)
})

Or globally, for all test suits by using configuring a setupTestFrameworkScriptFile like this:

// package.json
{
  "jest": {
    "setupTestFrameworkScriptFile": "<rootDir>/setupFramework.js",
  }
}

// setupFramework.js
import "called-with-immutable";

Related Work

custom-immutable-matchers include a Jest matchers package that adds new matchers to test an expectation for a specific Immutable.js type, e.g:

expect(new Immutable.Map()).toBeImmutable()

While custom-immutable-matchers tries to add additional functionality to via new matchers, we improve existing matchers and make the seamlessly work with Immutable.js data types.