Resetting the value of a mocked module in a Jest unit test - reactjs

Question

I'm trying to mock out methods in an imported module while testing a separate module. I'm able to successfully mock the imported module with ES2015 import syntax, but the mock stays consistent throughout the entire test and there are instances where I'd like to change the mock.
My files look like this
// ModuleA
import ModuleB from 'ModuleB'
// ... code
// TestCase
import ModuleA from 'ModuleA'
import ModuleB from 'ModuleB'
jest.mock('ModuleB', () => {
return {
value: true
}
}
describe('ModuleA', () => {
it('returns true', () => {
// This test expects ModuleB.value to return true
});
it('returns false', () => {
// This doesn't work
ModuleB.value = jest.fn(() => false)
// This doesn't work either
jest.mock('ModuleB', () => {
return {
value: false
}
});
// This test expects ModuleB.value to return false in order to pass
});
});
I essentailly need to separate mocks for ModuleB. In the past, I've been able to simply use var ModuleB = require('ModuleB'); instead of import and then call ModuleB.someMethodName = jest.fn() whenever needed. I'd like to use only ES2015 for these tests though, and using the pattern I just mentioned gives me a ModuleB is read-only error.

Answer 1

Use the requireActual method:
To ensure that a manual mock and its real implementation stay in sync, it might be useful to require the real module using require.requireActual(moduleName) in your manual mock and amending it with mock functions before exporting it.
For example:
const RealModule = require.requireActual('Form');
const MyModule = {
RealThing: RealModule.RealThing,
…add some mocks
};
References
jest.js Issue #1557: How to mock just the React components from a module exporting many things
jest.js Issue #1273: require.requireActual not returning the actual mock
Troubleshooting · Jest