Integration testing is the practice of checking how separate parts of a system behave once they are wired together. Where individual checks confirm each piece works alone, integration testing confirms they cooperate. It is a stage in the testing process rather than a single check.
Think of a relay race. Each runner can be fast on their own, but the race is won or lost at the baton handoff. Integration testing focuses on those handoffs across your software: the front end passing data to the back end, the back end writing to the database, the app calling an outside service. It builds on unit testing, which verifies each runner in isolation, and it is made up of many individual checks, each one being an integration test that exercises a specific connection.
There are two common ways to approach it. Bottom-up testing joins the lowest pieces first and works upward, while top-down starts at the outer flow and fills in the inner parts with stand-ins. Most teams mix the two, guided by where the riskiest connections sit.
Done well, integration testing fits into a wider quality assurance plan and runs often, so a change that quietly breaks a connection is caught the same day rather than weeks later in production. The pitfall is leaving it until the end, when every part lands at once and a single failure could be hiding in any of a dozen seams. Adding these checks gradually, as each connection is built, keeps that debugging cheap.
At TopDevs we treat integration testing as a routine part of building, so the connections that hold your system together keep working as it grows and changes.
