Which testing approach involves testing individual components or units of code?

Concept: Software testing is organized into levels based on the scope of what is being verified — from a single code unit, up through combined modules, to the complete system, and finally to overall business acceptance.

Application: The question asks for the approach that tests “individual components or units of code” in isolation. That is exactly what Unit Testing (also called component testing) does — a developer writes a focused test for one function, method, or class, typically using mocks or stubs to isolate it from its dependencies.

Cross-check: Contrasting what the other options actually test:

• Integration Testing checks how two or more already-unit-tested modules interact once combined — it operates above the single-unit level.

• System Testing evaluates the fully integrated application as a whole against overall requirements — again, not a single isolated unit.

• Acceptance Testing checks whether the finished system meets business and user needs before release — a delivery-readiness check, not a unit-level check.

Because only Unit Testing isolates and verifies a single component at a time, Unit Testing is the correct approach for this stem.