Unit test cases perform test checks and verify the code, but they only verify the inside logic of that particular part of the code, not the dependent module. For example, if service layer A method depends on service layer B method, and we are writing test cases for service A, we will mock service B. In this case, service layer A passes all its test cases and the same happens with service layer B. So, test cases for both service layers run perfectly fine individually, but not with each other. So, the verification of service layers is done on an individual level, but communicating with other service methods is also tested in the case of microservices.
This is where we introduce integration testing. It ensures that the all the different layer components work perfectly together and provide the expected results. For example, the data layer is getting data from the database, and the service layer is hitting the database layer and converting data into the desired format to send...