What integration testing is
Integration testing is a kind of software testing that checks whether different parts of a system work correctly when they are combined. While unit testing verifies individual pieces on their own, integration testing focuses on how those pieces work together. The goal is to catch problems that appear at the connections between parts, which may not show up when each part is tested in isolation.
Why combining parts matters
Even if each individual piece of a program works correctly on its own, problems can arise when the pieces are combined. The parts may not fit together as expected, or may make incorrect assumptions about each other. Integration testing addresses this by testing the pieces working together, revealing issues at the boundaries where one part connects to another.
How integration testing works
In integration testing, multiple units or components are brought together and tested as a group to see if they function correctly in combination. The tests check that data and control pass properly between the parts and that the combined behavior is correct. By exercising the interactions between components, integration testing verifies that the assembled pieces cooperate as intended.
Integration versus unit testing
Integration testing and unit testing are complementary. Unit testing checks the smallest pieces in isolation, while integration testing checks that those pieces work together correctly. A program can pass all its unit tests yet still fail when the parts are combined, which is exactly what integration testing is designed to catch. Both are important for thorough testing.
Where integration testing fits
Integration testing typically comes after unit testing, once the individual pieces have been verified, and before testing the complete system as a whole. It occupies a middle layer in the overall testing process, focusing on how components connect. This layered approach helps ensure that software is reliable at every level, from individual units up to the full system.
Why it matters
Integration testing is essential for catching the problems that only appear when parts of a system come together. Understanding what integration testing is - checking that combined components work correctly, not just individually - clarifies a key layer of software testing. For anyone interested in building reliable software, it is an important concept.
Related on Skillo
See also: What is unit testing? Explained, What is continuous integration (CI/CD)?.
Sources
Published date reflects the original event date (2024-05-21). This article is original Skillo editorial written from the sources above; facts were verified in September 2026.
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