Hi ✋, 

The hardest part of writing the unit test is creating mocks for external libraries, the purpose of this article is to help someone who has problems mocking a library like this.

Today I'm going to code how to mock your lambda invoke function in 'aws-sdk' using a jest 💪.

I'm going to write test cases for the below code. This is a simple cache service provider. it contains a getter and a setter.

CacheServiceProvider.ts

In here, I want to mock lambda.invoke function and want to set different responses to the promise resolve/reject.

This is my CacheServiceProvider.test.ts

Here I have fakePromise function and I can use jest mockImplementation method when I want to set response to the lambda.invoke().promise() 😁. If you need to change promise response , then you have to mock invoke function like invoke: () => fakePromise in the jest.mock("aws-sdk"). If this article helped you, please leave a comment. and also please leave your suggestions.