Learn in the textbookTest Techniques and Integration/Performance Verification
DefinitionIntegration testing (統合テスト) combines programs or components that have passed unit testing and checks whether their interfaces (インタフェース: the agreed rules for passing data and making calls) mesh correctly.
ExplanationAlso called 結合テスト in Japanese (literally a joining test), it checks the seams, because components that each work correctly on their own can still fail where they connect if the format or order of the values they pass does not match. Testing generally moves from unit testing (単体テスト) of each component, to integration testing, to system testing (システムテスト), where developers check the whole system against the requirements, and finally to operational testing (運用テスト), where users confirm it works for their business. Mapped to the development phases, integration testing verifies the output of internal design (内部設計), the phase that decides the system's internal structure.
AnalogyIt is like mounting an engine and a gearbox that have each passed inspection onto the car body, then checking that pressing the accelerator really turns the wheels.
Memory hook結合 literally means "tie and join": what you inspect is not each part but the knot between them.