When we write production-grade code, we want confidence that it behaves as expected. One of the main ways to achieve that is through unit tests — small automated checks verifying that specific parts of the code work correctly. Naturally, this raises a few questions: How many tests do we need? And how effective are they? A common answer is test coverage — a metric showing how much of the codebase is executed during testing. Many teams use test coverage as a quality gate: if the number drops below a threshold, new code can’t be merged. But these thresholds are often arbitrary — high enough to feel safe, yet low enough to be achievable. 75%, 80%, 85% — familiar numbers that might look meaningful but rarely are. Before relying on coverage as a quality signal, we should ask: What does test coverage actually tell us? How useful is it as a metric? Does a certain percentage guarantee well-tested code? This post explores those questions and shows why high coverage can still be misleading.…