Mocking globals in Jest

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As every test suite run its own environment, you can mock globals by just overwriting them. All global variables can be accessed by the global namespace:

global.navigator = {
  onLine: true
}

The overwrite has only effects in your current test and will not effect others. This also a good way to handle Math.random or Date.now.

Note, that through some changes in jsdom it could be possible that you have to mock globals like this:

Object.defineProperty(globalObject, key, { value, writable: true });

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