问题
I am writing tests using Jest for components that use canvas elements. I keep getting an error when I run my tests that looks like this.
Error: Not implemented: HTMLCanvasElement.prototype.getContext (without installing the canvas npm package)
From my understanding Jest uses jsdom for its testing and that jsdom is compatible with canvas if you install the canvas or canvas-prebuilt packages.
I have tried installing each of these packages and neither of them have resolved the error. The only thing that I think could be going wrong is that jsdom cannot find the canvas or canvas-prebuilt packages. Does anyone know a way to fix this error or test to see if jsdom is finding the other packages? Thanks a lot!
回答1:
You can create your own mock of the function in a jest setup script
HTMLCanvasElement.prototype.getContext = () => {
// return whatever getContext has to return
};
回答2:
My team is using create-react-app and we had previously addressed this problem by adding the npm package jest-canvas-mock. Now after upgrading to react-scripts 3.4.1, we also had to add a specific import to our src/setupTests.ts file:
import 'jest-canvas-mock';
回答3:
I had similar problem with my Jest tests, and solved it by installing jest-canvas-mock.
回答4:
Both answers above work. However, just wanted to add that in case of create-react-app, it doesn't support the 'setupFiles' required by jest conf in package.json for jest-canvas-mock.
I got around this by adding the import statement in each of the test files that were invoking the canvas element(in my case 3). Then, I moved the import statement to the setupTests.js file and removed that requirement as well.
来源：https://stackoverflow.com/questions/48828759/unit-test-raises-error-because-of-getcontext-is-not-implemented