What is the difference between integration testing and functional testing?

Integration testing verifies the interaction between individual modules or components of a program, exploring their integration with each other. The focus is on interfaces, data transfer, and identifying defects that occur during the modules' joint operation.

Functional testing checks whether the application's functionality meets the requirements of the specification. It tests what the system does, not how it does it. The focus is on inputs, outputs, and system behavior from the user's or business logic perspective.

Key differences:

Aspect	Integration Testing	Functional Testing
Purpose	Verify interaction between modules	Verify compliance with requirements and functions
Object of testing	Integrated modules/systems	Functional requirements/use case scenarios
Focus	Interfaces, data transfer, integration defects	Inputs, outputs, behavior according to specifications
Test basis	Architectural diagrams, module design	Requirements, user stories, specifications
Test examples	Data transfer between services	Correctness of salary calculation

Integration testing is often the next step after module testing, and functional testing can be conducted at various levels, including end-to-end system tests.