I have this React Component
export class Timer extends Component {
constructor(props) {
super(props);
this.state = {i : props.i};
}
componentDidMount(){
this.decrementCounter();
}
decrementCounter(){
if(this.state.i < 1){
return;
}
setTimeout(() => {
this.setState({i : this.state.i - 1})
this.decrementCounter()}, 1000);
}
render(){
return <span>{this.state.i}</span>
}}
And I want to express a test like this
jest.useFakeTimers();
it('should decrement timer ', () => {
const wrapper = shallow(<Timer i={10} />);
expect(wrapper.text()).toBe("10");
jest.runOnlyPendingTimers();
expect(wrapper.text()).toBe("9");
});
currently the first expect pass but the second fails
Expected value to be (using ===):
"9"
Received:
"10"
How can I properly test this component ?
Use Full Rendering API, mount(...)
Full DOM rendering is ideal for use cases where you have components that may interact with DOM APIs, or may require the full lifecycle in order to fully test the component (ie, componentDidMount etc.)
You can use mount()
instead of shallow()
like
import React from 'react';
import { mount, /* shallow */ } from 'enzyme';
import Timer from './index';
describe('Timer', () => {
it('should decrement timer ', () => {
jest.useFakeTimers();
const wrapper = mount(<Timer i={10} />);
expect(wrapper.text()).toBe("10");
jest.runOnlyPendingTimers();
expect(wrapper.text()).toBe("9");
jest.useRealTimers();
});
});
Or you can pass additional object to shallow
to instrument it to run lifecycle methods
options.disableLifecycleMethods: (Boolean [optional]): If set to true, componentDidMount is not called on the component, and componentDidUpdate is not called after setProps and setContext.
const options = {
lifecycleExperimental: true,
disableLifecycleMethods: false
};
const wrapper = shallow(<Timer i={10} />, options);
I tested it. It works.
hinok:~/workspace $ npm test
> c9@0.0.0 test /home/ubuntu/workspace
> jest
PASS ./index.spec.js (7.302s)
Timer
✓ should decrement timer (28ms)
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 8.162s
Ran all test suites.
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