1.5 KiB
Avoid using a callback in asynchronous tests (no-test-callback
)
Jest allows you to pass a callback to test definitions, typically called done
,
that is later invoked to indicate that the asynchronous test is complete.
However, that means that if your test throws (e.g. because of a failing
assertion), done
will never be called unless you manually use try-catch
.
test('some test', done => {
expect(false).toBe(true);
done();
});
The test above will time out instead of failing the assertions, since done
is
never called.
Correct way of doing the same thing is to wrap it in try-catch
.
test('some test', done => {
try {
expect(false).toBe(true);
done();
} catch (e) {
done(e);
}
});
However, Jest supports a second way of having asynchronous tests - using promises.
test('some test', () => {
return new Promise(done => {
expect(false).toBe(true);
done();
});
});
Even though done
is never called here, the Promise will still reject, and Jest
will report the assertion error correctly.
Rule details
This rule triggers a warning if you have a done
callback in your test.
The following patterns are considered warnings:
test('myFunction()', done => {
// ...
});
test('myFunction()', function(done) {
// ...
});
The following patterns are not considered warnings:
test('myFunction()', () => {
expect(myFunction()).toBeTruthy();
});
test('myFunction()', () => {
return new Promise(done => {
expect(myFunction()).toBeTruthy();
done();
});
});