I understand why this is happening, but I've not found a way to enable me to mock axios and not have the client field be undefined. The problem arises when I mock the axios dependency with jest.mock('axios') - A TypeError is being thrown in the test when an attempt is made to call axios.get: TypeError: Cannot read property `get` of undefined In the constructor of my API class I pass in a URL, and use the axios.create function to create a custom instance of axios and bind it to the the client property. In the unit tests I am mocking axios using Jest. I am writing a JS API client that wraps the underlying axios library. This would allow me to catch any changes in my node_module constructor contract, while also reducing the number of assumptions I make in my code.New to node.js. Instead of relying on a particular structure returning from bunyan and hard coding that in to my tests, I could consider unmocking the bunyan module, making a call to the constructor with valid configuration to get the shape of the logger, and then using something like jest-mock-object all of the object methods with jest.fn() for spying purposes. If the structure returned from Bunyan ever changed in a breaking way, my tests as currently written would not fail. But I have trouble handling the new constructor with parameters.
#Jest mock constructor code
I have code that mocks TableName.query (hashkey).eq (myhashkey).exec () and similar queries. I need help mocking new TableName (params).save () used to create a new Dynamoose object in Jest. The astute reader will notice that I’m relying on a particular structure / method name being returned from the bunyan constructor (the mockBunyanLogger makes this assumption). Mock a new object creation with constructor parameters in jest.
#Jest mock constructor how to
Since the mockBunyanLogger object reference is in my test file, I can reference the mock methods in my expectations. TIL how to mock the constructor function of a nodemodule during unit tests using jest. Wouldn't it be possible to bypass this dependency by mocking like this: jest.mock('././repo') // Creates a mock of the entire class (as long as it's the default export) const mockRepo: IRepo new (Repo as any)() // Repo is an 'any' type so we don't have to inject a dependency Since we're building the mock from the imlementation rather than the interface, could also more honestly type it as. The mockImplementation step says “when the Bunyan constructor is called, return this mockBunyanLogger object in place of the original”. It is a key tool for following RTL’s best practice of. Mocking is a core tenet of unit-testing a React application. If you are not familiar with the general testing structure of React, I recommend starting with. Note: This article assumes a basic understanding of Jest and the React Testing Library. jest mock function jest mock functions from module jest mock api calls jest mock return value jest mock constructor jest mock defined function mock file jest jest mock instance type jest mock same function twice jest mock window jest.mock typescript mock a function jest react jest mock called once jest mock my own module jest mock. logger.js const Bunyan = require ( ' bunyan ' ) const bunyanLogger = new Bunyan () Using Jest Mocks + TypeScript the Right Way. We recently integrated the bunyan structured logger into our app, and unlike the Raven service provided by sentry for client-side logging, bunyan provides a constructor for initialization, which returns a configured logger. I ran into a testing scenario where straight automocking was not sufficient for what I needed to test. Automocking the module will suffice for most testing scenarios you come up with, since it allows you to separate behavior of the module from the way your application code uses it.
TIL how to mock the constructor function of a node_module during unit tests using jest.Īs noted in my previous post, jest offers a really nice automocking feature for node_modules.
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