问题
I am developing a React app using Typescript, and hooks, and I am trying to use Enzyme with Jest to test the function components. I am unable to use jest.spyOn to test a method in my component. The jest.spyOn method doesn't resolve correctly and shows following message on hover
"Argument of type '"validateBeforeSave"' is not assignable to parameter of type '"context" | "setState" | "forceUpdate" | "render" | "componentDidMount" | "shouldComponentUpdate" | "componentWillUnmount" | "componentDidCatch" | "getSnapshotBeforeUpdate" | ... 6 more ... | "UNSAFE_componentWillUpdate"'.ts(2345)"
I tried to cast the instance as 'Any' -
const instance = wrapper.instance() as any;
This of course ignores the problem at compile time, but then the test throws a runtime error that function does not exist on component.
Cannot spy the validateBeforeSave property because it is not a function; undefined given instead
// Some function Component
const SomeComponent = (props: IMyComponentProps) => {
const { classes } = props;
// Component has state
const [count, setCount] = useState(0);
function validateBeforeSave(){
}
function handleClick() {
validateBeforeSave();
.
.
.
}
return (
<div>
<Button>
className="saveBtn"
onClick={handleClick}
</Button>
</div>
);
};
// Unit test
describe('SomeComponent' () => {
it('validates model on button click', () => {
const wrapper = mount(
<MuiThemeProvider theme={theme}>
<SomeComponent/>
</MuiThemeProvider>,
);
const instance = wrapper.instance();
const spy = jest.spyOn(instance, "validateBeforeSave");
wrapper
.find('.saveBtn')
.at(0)
.simulate('click');
expect(spy).toHaveBeenCalledTimes(1);
});
}
What am I missing here? How does spyOn work with function components?
I created the app using the create-react-app template and it has these dependencies for test packages
"devDependencies": {
"ts-jest": "^23.10.3",
"@types/jest": "24.0.9",
"@types/enzyme": "^3.9.1",
"@types/enzyme-adapter-react-16": "^1.0.2",
"enzyme": "^3.9.0",
"enzyme-adapter-react-16": "^1.11.2",
"enzyme-to-json": "^3.3.5",
}
回答1:
Posting my comment here again to answer your question: Your validateBeforeSave
function is declared within SomeComponent
making it a closed/private scope function not accessible outside. You can pass that function as a prop and you can then create spy and pass it as a prop value in your test and test for if the prop function passed (spy) was called or not
So you would modify your function somewhat like this:
// some validator function
function validateBeforeSave(){
...
}
// Some function Component
const SomeComponent = (props: IMyComponentProps) => {
const { classes, validateBeforeSave } = props;
// Component has state
const [count, setCount] = useState(0);
function handleClick() {
validateBeforeSave();
.
.
.
}
return (
<div>
<Button>
className="saveBtn"
onClick={handleClick}
</Button>
</div>
);
};
And In your Unit test, something like this:
// Unit test
describe('SomeComponent' () => {
it('validates model on button click', () => {
const validateSpy = jest.fn();
const wrapper = mount(
<MuiThemeProvider theme={theme}>
<SomeComponent validateSpy={validateSpy}/>
</MuiThemeProvider>,
);
const instance = wrapper.instance();
wrapper
.find('.saveBtn')
.at(0)
.simulate('click');
expect(validateSpy).toHaveBeenCalledTimes(1);
});
}
回答2:
I was also facing the same issue - I did like below -
import * as React from 'react';
const SampleComponent = () => {
const sampleMethod = () => {
console.log('hello world');
};
return <button onClick={sampleMethod} type="button">Click Me</button>;
};
export default SampleComponent;
test -
import React from 'react';
import SampleComponent from './';
import { shallow } from 'enzyme';
describe('SampleComponent', () => {
test('should handle click correctly', () => {
const logSpy = jest.spyOn(console, 'log');
const wrapper = shallow(<SampleComponent></SampleComponent>);
const button = wrapper.find('button');
expect(button.text()).toBe('Click Me');
button.simulate('click');
expect(logSpy).toBeCalledWith('hello world');
});
});
We can spy on console.log, to assert it is to be called or not
Check - https://stackoverflow.com/a/58637912/10734622
来源:https://stackoverflow.com/questions/56297482/how-to-use-jest-spyon-with-react-function-component-using-typescript