Add Turn Off Console Error Messages In A Test as a javascript til

javascript/turn-off-console-error-messages-in-a-test.md

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+# Turn Off Console Error Messages In A Test
+
+I'm using [Jest](https://facebook.github.io/jest/) to test a React component
+that requires a prop via
+[PropTypes](https://reactjs.org/docs/typechecking-with-proptypes.html). In
+one of my tests, I want to test that component when the required prop is
+excluded. The side effect of doing this is that my test output gets
+cluttered with the PropType warning.
+
+The thing to do is silence the error message during that test.
+
+```javascript
+it('renders a component without a required prop', () => {
+  const originalError = console.error;
+  console.error = jest.fn();
+
+  // test code here
+  expect(shallow(<My Component />)).toDoSomething;
+
+  console.error = originalError;
+});
+```
+
+We can silence `console.error` by temporarily replacing it with a
+Jest-mocked function and then putting it back at the end of the test.