Try Hard

tryHard is a convenient tool when writing your Javascript tests and you need to test asynchronous state changes with no control on the timing.
It is particularly useful for integration tests.

API

tryHard takes as a first argument a function that can fail (ie. that throws) or that can pass (ie. that doesn't throw)

It calls the function many times (by default every 25ms) until:

• it finally passes
• or it reached the timeout (by default 2 seconds), in which case it fails and rethrow the error of the inner function

tryHard returns a promise. You can use the .then() and .catch() to end your test.
The easiest way is to use ES7 async/await and simply await tryHard() in your test

async function tryHard(testable: Function, options?: TryHardOptions)
 
type TryHardOptions = {
  interval?: number, // time in milliseconds between each try
  timeout?: number, // time in milliseconds to wait before failing
}

Examples

Typical example when writing an integration test:

it('updates the application state', async () => {
  assert(myApplicationState.dataIsFetched === false);
  myApplicationState.fetchSomeData();
 
  await tryHard(() => {
    assert(myApplicationState.dataIsFetched === true);
  });
});

Very useful also when testing the DOM, here an example with Enzyme:

it('updates the DOM', async () => {
  assert(wrapper.find('ListOfItems').length === 0);
  myReduxStore.dispatch(fetchTheItems());
 
  await tryHard(() => {
    assert(wrapper.find('ListOfItems').length === 10);
  });
});

Old school promises also work of course :

it('updates the application state', (done) => {
  assert(myApplicationState.dataIsFetched === false);
  myApplicationState.fetchSomeData();
 
  tryHard(() => {
    assert(myApplicationState.dataIsFetched === true);
  }).then(() => done()).catch(err => done(err));
});

Prerequisites

You can require directly the function in src/index.js if you are in a ES2016 environment that support async/await (or if you use Babel)

Otherwise don't forget to include regenerator-runtime:

npm install --save regenerator-runtime

And then in your entry-point:

require('regenerator-runtime/runtime');