React default props are eagerly evaluated in tests.

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

A bug

What is the current behavior?

As soon as a React component is imported from a test, its defaultProps evaluate, even without rendering the component.

See this repo demonstrating the behavior.

What is the expected behavior?

Default props would not be evaluated unless the component is rendered. Otherwise, it’s a leaky abstraction. In this case, two unrelated components use moment differently, which I’m mocking in a test. I shouldn’t need to know all the ways moment gets used, just the way it’s used in the component(s) I’m rendering.

Please provide your exact Jest configuration and mention your Jest, node, yarn/npm version and operating system.

Jest - 22.4.2 node - 8.4.0 npm - 5.6.0 OS - OS X 10.12.6

[rickhanlonii]

The defaultProps object is defined in the top level scope of the module, so it’s evaluated when the module is imported. This isn’t specific to defaultProps, any object declared in the top level of a module will be evaluated when the module is imported – this is how the module’s scope is formed

Consider this example:

// foo.js
const someFunction = () => {
  console.log('someFunction will be called when module is imported');
  return 'bar';
};

export const anyObject = {
  foo: someFunction(),
};

// foo.test.js
import { anyObject } from './foo';

test('expected', () => {
  expect(anyObject).toEqual({ foo: 'bar' });
});

If you have more questions, I’m happy to help on our discord channel or StackOverflow where there is an active jestjs tag for questions

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