Test Coverage

Test Coverage

Test coverage is a way to measure how much of a program's code is exercised by automated tests. It tells you which lines, functions, or decision points have been run while tests are executed, and whether parts of the codebase are never touched by checks. High coverage means many parts of the code have been run by tests, while low coverage reveals areas that could hide bugs. This matters because untested code can behave unexpectedly in real use and cause failures that are costly to fix. However, coverage is a guide, not proof that software is correct. Tests can execute a line without verifying the result, so numbers alone don't guarantee quality. Developers use tools to visualize untested code and prioritize where to add meaningful checks, focusing on critical features and user-facing behavior rather than chasing a perfect percentage. Overreliance on coverage can lead to superficial tests written just to raise the metric, so it’s best used alongside careful test design, code reviews, and real-world scenarios to improve confidence in the software.