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Unit vs Integration vs System vs E2E Testing

The table below illustrates the most critical characteristics and differences among Unit, Integration, System, and End-to-End Testing, and when to apply each methodology in a project.

Unit Test Integration Test System Testing E2E Test
Scope Modules, APIs Modules, interfaces Application, system All sub-systems, network dependencies, services and databases
Size Tiny Small to medium Large X-Large
Environment Development Integration test QA test Production like
Data Mock data Test data Test data Copy of real production data
System Under Test Isolated unit test Interfaces and flow data between the modules Particular system as a whole Application flow from start to end
Scenarios Developer perspectives Developers and IT Pro tester perspectives Developer and QA tester perspectives End-user perspectives
When After each build After Unit testing Before E2E testing and after Unit and Integration testing After System testing
Automated or Manual Automated Manual or automated Manual or automated Manual

Last update: August 17, 2022