Integration Tests vs Unit Tests: What Are They And Which One to Use?

Unit testing and integration testing are two fundamental stages in the software testing process, each serving distinct purposes and occurring at different stages of development. Unit testing involves examining individual components or modules in isolation, often using mocked data, to ensure each piece of code performs its intended function. This type of testing is typically done by developers and is cost-effective due to its simplicity and speed, as it doesn't require external resources or environments. Conversely, integration testing evaluates the interaction between combined modules to ensure they function together seamlessly, identifying bugs that unit tests might miss, such as those arising from different developers' contributions. Although integration tests are generally more complex and resource-intensive, they provide crucial feedback about the system's overall functionality. While unit tests are executed early and frequently, integration tests follow to verify the system’s coherent operation, and both testing types are integral to producing reliable software.