Support for testdouble.js for users of Jest!
Note that testdouble-jest requires testdouble@3.6.0 and jest@21.0.0 or higher to work.
$ npm i -D testdouble-jest
Then, from a test helper (we recommend setting a
setupFilesAfterEnv
module), invoke the module and pass in both td and jest, like so:
global.td = require('testdouble')
require('testdouble-jest')(td, jest)For an example of a helper that sets up testdouble.js, testdouble-jest, and
ensures td.reset() is called after each test, look at
example/helper.js in this repo.
When you invoke testdouble-jest, it does two things: (1) adds support for
using td.replace() for module replacement in Jest tests, and (2) adds a new
top-level td.mock() function that mirrors the jest.mock() API.
We recommend using td.replace(), since it's terser (by returning the fake
instead of the jest object) and your use of testdouble.js will remain portable
even if you were to move to a different test runner.
td.replace(moduleName[, manualStub])
Once you've initialized testdouble-jest in your test run, td.replace() will be
able to replace modules just as it does in any other test runner (as of
testdouble@3.5.0). Functionally, it's delegates to td.mock(), but behaves just
as it always
has
for module replacement.
Here's a trivial example:
let loadInvoices, subject
describe('td.replace', () => {
beforeEach(() => {
loadInvoices = td.replace('./load-invoices')
subject = require('./calculate-payment')
})
it('calculates payments', () => {
td.when(loadInvoices(2018, 7)).thenReturn([24,28])
const result = subject('2018-07')
expect(result).toEqual(52)
})
})For a runnable example, check example/td-replace.test.js.
td.mock(moduleName[, moduleFactory, options])
td.mock() is designed to have the same API as
jest.mock().
If you just pass a module name to td.mock(), it will imitate the real
dependency and use Jest's own module replacement facility to ensure that any
require() calls by your test subject receive the testdouble fake, as opposed
to the real dependency. There's an example in this repo at
example/td-mock.test.js.
If you've used jest.mock() before, td.mock() will seem pretty familiar.
td.mock() returns the jest object (since that's what
jest.mock() does), so your test will also need to require() the thing you
just faked if you want to set up any stubbings or invocation assertions.
Note that if you provide a moduleFactory and/or options argument, td.mock
will simply delegate to jest.mock, since it won't have anything
testdouble.js-specific to do.