How to mock navigator.clipboard.writeText() in Jest?

Question

I have tried the following 4 options after looking at Jest issues and SO answers, but I am either getting TypeScript errors or runtime errors. I would really like to get option 1 (spyOn) working.

// ------ option 1 -----
// Gives this runtime error: "Cannot spyOn on a primitive value; undefined given"
const writeText = jest.spyOn(navigator.clipboard, 'writeText');

// ------ option 2 -----
Object.defineProperty(navigator, 'clipboard', {
    writeText: jest.fn(),
});

// ------ option 3 -----
// This is from SO answer but gives a TypeScript error
window.__defineGetter__('navigator', function() {
    return {
        clipboard: {
            writeText: jest.fn(x => x)
        }
    }
})

// ------ option 4 -----
const mockClipboard = {
    writeText: jest.fn()
};
global.navigator.clipboard = mockClipboard;

Answer 1

Jest tests are running in JSdom environment and not all of the properties are defined, but so you should define the function before spying on it.

Here is an example:

Object.assign(navigator, {
  clipboard: {
    writeText: () => {},
  },
});

describe("Clipboard", () => {
  describe("writeText", () => {
    jest.spyOn(navigator.clipboard, "writeText");
    beforeAll(() => {
      yourImplementationThatWouldInvokeClipboardWriteText();
    });
    it("should call clipboard.writeText", () => {
      expect(navigator.clipboard.writeText).toHaveBeenCalledWith("zxc");
    });
  });
});

Edit: you can also use Object.defineProperty, but it accepts descriptors object as third parameter

Object.defineProperty(navigator, "clipboard", {
  value: {
    writeText: () => {},
  },
});

Answer 2

I ran into a similar situation and used the following method to mock the clipboard in the navigator object:

  const originalClipboard = { ...global.navigator.clipboard };
  const mockData = {
     "name": "Test Name",
     "otherKey": "otherValue"
  }

  beforeEach(() => {
    const mockClipboard = {
      writeText: jest.fn(),
    };
    global.navigator.clipboard = mockClipboard;

  });

  afterEach(() => {
    jest.resetAllMocks();
    global.navigator.clipboard = originalClipboard;
  });

  test("copies data to the clipboard", () => {
    copyData(); //my method in the source code which uses the clipboard
    expect(navigator.clipboard.writeText).toBeCalledTimes(1);
    expect(navigator.clipboard.writeText).toHaveBeenCalledWith(
      JSON.stringify(mockData)
    );
  });