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 deviations from the happy path within your context blocks. Unfortunately, I can’t seem to do this with Jest. I’ve tried the following: Because jest executes every describe block before running any specific describe block, input is always ‘baz’. Does anyone know a work around, or

Using Spies and Mocks on complex objects with Jest

I’m fairly new to testing and writing tests for a currently uncovered javaScript codebase using Jest. The code covers some niche use cases, as its conditionally injected and executed by the browser during page load. Anyway, I’m having issues mocking up custom objects. Here’s the function in question: As far as I understand, I need to mock both window.location.pathname to return a string, and I need to mock window.TOOL.cookie.setCookie() as a mock function. Here’s my attempt at the test: The test fails, saying that window.TOOL.cookie.setCookie was called 0 times. I’ve dug into the process, and found that window.location.pathname is executing

Express POST API Route not receiving a Supertest request

I am trying to test an Express API POST Route that uses Express Validator for check: This API route expects to receive a request consisting of a body that contains the fields, name, email, and password: In order to test this route, I have a test file using supertest and jest: When I execute this test, each check in the POST API route fails. The following errors is returned: Why is the API route not receiving the request I’m sending using Supertest? Answer Well, it seems that you’re not sending your values right. Look closely at where you send your

Jest | TypeError: window.URL.createObjectURL is not a function

This issue happens due to be using mapbox-gl in a React project. I’m aware that there are solutions like this but due to me being a junior I fail to completely comprehend what I should do to solve. I don’t have any setupTest.js or jest.stubs.js Creating them appears to do nothing for my test suites. I’m using ftw-hourly for this project and I added mapbox-gl and @mapbox/mapbox-gl-geocoder as dependencies. Can someone guide me on how to solve this? Answer There’s an important distinction here. This issue is happening because your tests are invoking mapbox-gl, but it is not because you

How to set env in package.json which is used within .bablerc

I am trying to run Jest tests as part of a script before I then run webpack, like this. Jest only works with compiled code, so I had set my .babelrc to the following, which worked, however then it transpiled all my code in webpack which I didn’t want, in development mode I want to leave the JavaScript un-transpiled so I can work with it without it being obfuscated. Instead I want to run Jest by calling ‘npm run test’ which then I can specify only that script transpiles the code and then webpack runs without transpiling, I was hoping

Error: Not implemented: window.scrollTo. How do we remove this error from Jest test?

The error: Because we are using window.scrollTo(0,0). Also getting Not implemented Navigation for: window.location.replace(externa_link) same error happens with .assign. I tried googling for solutions with react-router, but all examples use some component which contains window.location. Is there a way to avoid this error? Or hide it? I did some research and found that the Facebook team isn’t going to address it. Is there a way to suppress these errors/warnings when running jest test? Our code doesn’t break and all tests pass otherwise. Answer Try running the jest command with –env=jsdom. This will mock most browser functions and will solve your

Using sinon how do I stub or fake the property of a callback

Using sinon how do I stub/fake a return value for this.lastID in the function. I can fake the callback using this code: But it will fail as this.lastID is undefined. How do I overcome this? Thanks! Answer You can use stub.callsArgOn() to pass in a context value that will used as this in the callback. You would stub it with something like: Here’s an example with some made up functions:

How to determine if JEST is running the code or not?

I am creating a JS test on my react-native project. I’m specifically using firebase for react native, in which I would like to replace firebase instance with a mockfirebase instance if JS is running the code of my class. For example I have class setup like below. I’d like to have a check if jest is the running environment then I’d replace the import line with appropriate mock class. Answer jest sets an environment variable called JEST_WORKER_ID so you check if this is set: I also see that if NODE_ENV is not set the jest CLI sets it to the

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 file jest/setup.js: I’ve configured jest to run this setup file by adding this line into packages.json: