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TypeScript / Test parameter passed into a function with Jest

OK, this one is super useful, I promise!

As you may already know, we can use toHaveBeenCalledWith on a spied function to check if that function has been called with a set of arguments.

For example, the following code test the apiService.get to be called with a correct URL when ping is invoked.

const ping = (name: string) => {
    return apiService.get(`/api/ping?user=${name}`);
};
 
test('ping should call correct URL', () => {
    const getSpy = jest.spyOn(apiService, 'get');
    ping('huy');
    expect(getSpy)
        .toHaveBeenCalledWith('/api/ping?user=huy');
});

What if you only want to test just a small part of an URL parameter that has been passed to apiService.get?

You can use expect.stringContaining as a parameter of toHaveBeenCalledWith!

test('ping should call with URL containing correct name', () => {
    const getSpy = jest.spyOn(apiService, 'get');
    ping('huy');
    expect(getSpy)
        .toHaveBeenCalledWith(expect.stringContaining('huy'));
});