I have a file with object that gets populated with process.env properties: env.js Now I try to test this file with different process.env properties: env.test.js Unfortunately, even though I try to load the file in every test separately the file gets loaded only once, making the third test fail with: P.S. It d…
Tag: jestjs
How can I test for object keys and values equality using Jest?
I have a mapModule where I import components and export them: How can I test that mapModule has the correct exported keys, values and that they are not null or undefined? Answer In version 23.3.0 of jest, expects a string. Use: result is passing test
Mock a dependency’s constructor Jest
I’m a newbie to Jest. I’ve managed to mock my own stuff, but seem to be stuck mocking a module. Specifically constructors. usage.js I’d like to do something like this in the tests. However when I come to use it in usage.js the cw is a mockConstructor not a FakeMetrics I realise that my appro…
Error is thrown but Jest’s `toThrow()` does not capture the error
Here is my error codes: As you can see the error did indeed occurred: Function FunctionThatDoesNotExistsInString does not exists in string.. However it is not captured as a pass in Jest. Here is my codes: Answer expect(fn).toThrow() expects a function fn that, when called, throws an exception. However you are…
Getting `TypeError: jest.fn is not a function`
I’m trying to create the following unit test using Jest. But I’m getting the following error after running npm test. TypeError: jest.fn is not a function This is some section of my package.json: What could be the reason I’m getting that error? Answer The jest object is automatically in scope…
How to mock functions in the same module using Jest?
What’s the best way to correctly mock the following example? The problem is that after import time, foo keeps the reference to the original unmocked bar. module.js: module.test.js: I could change: to: but this is pretty ugly in my opinion to do everywhere. Answer fwiw, the solution I settled on was to u…
How to change the behaviour of a mocked import?
I am quite confused with mocking in Jest an how to unit test the implementations. The thing is i want to mock different expected behaviours. Is there any way to achieve this? as imports can be only on the top of the file and to be able to mock something it must be declared before the import. I have also
How to test properly React Dropzone onDrop method
I’m testing React Dropzone and I need to check the onDrop function. This function has two parameters (acceptedFiles and rejectedFiles). I’m mocking the files like this: Then in my test, I do that: This is my onDrop function: The expected result would be that handleOnDrop returns acceptedFiles but …
Jest equivalent to RSpec lazy evaluated variables (let)?
In rspec you can do something like this: This allows you to define a method call or instantiation of a large object as a sum of its smaller parts. You can then override those individual small parts inside different contexts. The idea being that you create a happy path before each test, and then specify deviat…
How to mock Push notification native module in React native jest tests?
When using the module react-native-push-notification, I had this error: I tried to mock the module by creating __mocks__/react-native.js and putting this code within it: Now, I have this error: How I could mock fully this module the right way? Answer I mocked the module PushNotificationIOS by creating a setup…