Is 100% Code Coverage Worth Chasing?

Many engineering teams set ambitious targets like 90% or even 100% code coverage, believing that the highest number must mean the strongest quality. But coverage is only a metric that shows which lines executed during testing — not whether the tests validated correct behavior.

A suite full of shallow tests can hit every line while still missing critical defects in logic, boundary conditions, or error handling. Conversely, a slightly lower coverage score paired with thoughtful, high-value tests often delivers far better production reliability.

A more practical approach is to interpret code coverage through the lens of risk and impact:

Which parts of the system hold core business logic?

Where do failures have the highest cost?

What areas change frequently and need stronger regression confidence?

Instead of chasing 100%, teams benefit more from purpose-driven coverage — targeting complex paths, edge cases, and unstable modules. Code coverage works best as a diagnostic signal, guiding improvements rather than acting as a trophy metric. Quality isn’t measured by how much code is touched, but by how well the system is protected from real-world failures.