Expect Gen

As in “expect generator…”. An assertion / snapshot library for testing iterators and generators. It was designed for, and works particularly well with, redux-saga but can be used for anything that uses generators.

Example

function* myEffect(fakeAction) {
  const fooIds = yield select(fooIds);
  yield put(foosLoading());
  const results = yield call(apiFetch, options);
}
import expectGen from 'expect-gen';
it('runs effect with fakeFooIds and fakeResults', () => {
  expectGen(myEffect, fakeAction)
    // asserts step yields first `select(fooIds)`
    .yields(
      select(fooIds),
      // `fakeFooIds` gets pass into the following `next`
      fakeFooIds
    )
    .yields(
      put(foosLoading())
    )
    .yields(
      call(apiFetch, options),
      fakeResults
    )
    .finishes()
    .run();
});
it('runs effect with fakeFooIds and fakeResults', () => {
  const snapshot = expectGen(myEffect, fakeAction)
    // Doesn't run assertion for `next`
    .next(fakeFooIds)
    .next()
    .yields(
      call(apiFetch, options),
      fakeResults
    )
    .finishes()
    .toJSON();
  expect(snapshot).toMatchSnapshot();
});

API

expectGen

expectGen(generator, [...args])

Calls the first argument with the rest of the arguments
Returns instance of StepManager

StepManager

expectGen returns an instance StepManager. It gives us a set of chainable methods:

yields

expectGen(generator, [...args])
  .yields(expectedValue, [result])

Runs an assertion that iterator will yield the expectedValue
Passes result into generator’s next method
Returns same instance StepManager

expectGen(generator, [...args])
  .next([result])

Passes result into generator’s next method
Makes no assertion
Returns same instance StepManager

throws

expectGen(generator, [...args])
  .throws(error)

Throws error into generator
Checks that iterator throws an uncaught exception
Returns same instance StepManager

catches

expectGen(generator, [...args])
  .catches(error, [expectedValue])

Throws error into generator
Runs an assertion that thrown iterator will yield the expectedValue
Returns same instance StepManager

catchesAndFinishes

expectGen(generator, [...args])
  .catchesAndFinishes(error, [result])

Throws error into generator
Asserts that generator finishes with result
Returns same instance StepManager

finishes

expectGen(generator, [...args])
  ...
  .finishes([result])

Asserts that generator finishes with result
Returns same instance StepManager

run

expectGen(generator, [...args])
  ...
  .run()

Executes all assertions
Returns results of all generator steps as an array

toJSON

expectGen(generator, [...args])
  ...
  .toJSON()

Convert results from run() into a JSON object

Roadmap

Expect Gen is heading towards v1. The following items still need to go in before then. Please open issues for other v1 requirements you find.

v1.0.0

Previous Version

Expect Gen is a second generation version of generator-test-runner. Many of the concepts used here originated there.