React Enzyme - Test `componentDidMount` Async Call

Question

everyone.

I\'m having weird issues with testing a state update after an async call happening in componentDidMount.

Here\'s my component code:

Answer 1

You can abstract the user list retrieval away from the react component via passing a function that returns a Promise so that instead of

  componentDidMount() {
    request('https://api.github.com/users', (err, res) => {
      if (!err && res.statusCode === 200) {
        this.setState({
          usersList: res.slice(0)
        });
      }
      else {
        console.log(err);
      }
    });
  }

Replace it with

  componentDidMount() {
     var comp = this;
     this.props.getUsers()
        .then(function(usersList) {
          comp.setState({
            usersList: usersList
          });
        })
        .catch(function (err) {
            console.log(err);
        });
  }

And inside your test mock that getUsers function:

    it('Correctly updates the state after AJAX call in `componentDidMount` was made', (done) => {

      let resolveGetUsers;

      let getUsers = function() {
        return new Promise(function (resolve, reject) {
                  resolveGetUsers = resolve;
                });
      }

      let wrapper = mount();

      resolveGetUsers([{ "name": "Reign", "age": 26 }]);


      // promise resolve happens in a subsequent event loop turn so move assertions inside setImmediate
      setImmediate(() => {

        expect(wrapper.update().state().usersList).to.be.instanceof(Array);
        ...

        done();
      });
    }

Note that I have done this and it works for me (even without the wrapper.update() part) and here I tried to apply it to your code example without running it..

Also note that it should work in cases other then componentDidMount too - like having an async action triggered after clicking a button for example..