The basic idea of unit testing is that you are testing individual units of source code that you have written to see if there are any bugs. Usually the code is deterministic so there are set outputs. The idea of integration testing is to test how a group of modules in your application are working together including how external dependencies are working with the code. This usually involves testing something that is non-deterministic in the application.

Integration testing usually comes after unit testing and is the more expensive to maintain. While the developers will run the unit tests, integration tests are usually required to be ran by a test team. This is partly due to the difficulty in finding errors in integration tests as well as the time it takes.

Integration testing is black box testing which means you are testing the inputs and outputs of the interface. An example of an integration test would be checking the interface to see if you are brought to your profile home page when you enter your username and password. Unit testing is white box testing so you are writing test cases for certain functions to see if they perform correctly. An example of a unit test would be writing a JUnit test case to test the deposit() method and assert that when you make a deposit of $50 to your bank account object (with initial balance of $0) that your balance is now at $50.

The main takeaway is that integration testing tests the interface and how multiple modules work together while unit testing is testing the source code of one function. Unit tests are done in early development while integration tests are done after you have some sort of product complete.

Sources:

https://www.guru99.com/integration-testing.html#3

From the blog CS@Worcester – Austins CS Site by Austin Engel and used with permission of the author. All other rights reserved by the author.