add option to fail tests that print errors and warnings

Do you want to request a feature or report a bug?

Feature.

What is the current behavior?

Tests pass even if they print errors and warnings to the console.

What is the expected behavior?

It would be nice if we could force the test to fail.

Our test suite prints lots of things like this:

    console.warn node_modules/moment/moment.js:293
      Deprecation warning: value provided is not in a recognized RFC2822 or ISO format. moment construction falls back to js Date(), which is not reliable across all browsers and versions. Non RFC2822/ISO date formats are discouraged and will be removed in an upcoming major release. Please refer to http://momentjs.com/guides/#/warnings/js-date/ for more info.

    console.error node_modules/fbjs/lib/warning.js:33
      Warning: Each child in an array or iterator should have a unique "key" prop.

(node:15601) UnhandledPromiseRejectionWarning: SyntaxError: The string did not match the expected pattern.

    console.error node_modules/fbjs/lib/warning.js:33
      Warning: `value` prop on `input` should not be null. Consider using an empty string to clear the component or `undefined` for uncontrolled components.

These are all legitimate errors that we should fix, yet our automated tests pass. If Jest could be made to fail, that would encourage developers to keep the tests clean.

[greypants]

Here’s the variant I landed on, using Node’s Util.format function to preserve console string formatting via arguments in the error output:

// setupTests.js
import { format } from "util";

const error = global.console.error;

global.console.error = function(...args) {
  error(...args);
  throw new Error(format(...args));
};

cc @akx, re:

Error: Warning: Received %s for a non-boolean attribute %s.

[apaatsio]

This can already be achieved with a couple lines of code.

const spy = jest.spyOn(global.console, 'error')
// ...
expect(spy).not.toHaveBeenCalled();