How do I test async code with mocha? I wanna use multiple await
inside mocha
var assert = require('assert'); async function callAsync1() { // async stuff } async function callAsync2() { return true; } describe('test', function () { it('should resolve', async (done) => { await callAsync1(); let res = await callAsync2(); assert.equal(res, true); done(); }); });
This produces error below:
1) test should resolve: Error: Resolution method is overspecified. Specify a callback *or* return a Promise; not both. at Context.it (test.js:8:4)
If I remove done() I get:
1) test should resolve: Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/tmp/test/test.js)
Writing Asynchronous Tests with Mocha. To indicate that a test is asynchronous in Mocha, you simply pass a callback as the first argument to the it() method: it('should be asynchronous', function(done) { setTimeout(function() { done(); }, 500); });
If a function returns a promise that you want to assert on the result of the function, all you need to do for it to work effectively with Mocha is return the promise in your it block. Then you can assert on the result of the promise in the chained . then of your promise.
This illustrates the first lesson from the async/await conceptual model: To test an asynchronous method's behavior, you must observe the task it returns. The best way to do this is to await the task returned from the method under test.
Mocha supports Promises out-of-the-box; You just have to return
the Promise to it()
's callback. If that Promise resolves then the test passes otherwise it fails.
Since async
functions always implicitly return a Promise
you can just do:
async function getFoo() { return 'foo' } describe('#getFoo', () => { it('resolves with foo', () => { return getFoo().then(result => { assert.equal(result, 'foo') }) }) })
You don't need done
nor async
for your it
.
async/await
:async function getFoo() { return 'foo' } describe('#getFoo', () => { it('returns foo', async () => { const result = await getFoo() assert.equal(result, 'foo') }) })
done
as an argumentIf you use any of the methods described above you need to remove done
completely from your code. Passing done
as an argument to it()
hints to Mocha that you intent to eventually call it.
Using both Promises and done
will result in:
Error: Resolution method is overspecified. Specify a callback or return a Promise; not both
The done
method is only used for testing callback-based or event-based code.
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