Common Software Testing Antipatterns and the Real Meaning of Code Coverage

The article continues a series on software testing, linking to the original post and author, and focuses on three new testing misconceptions.

Misconception 4 – Testing the Wrong Functionality: Developers often waste time writing tests for low‑impact code while neglecting critical features. A mental model classifies code into critical , core , and other layers, urging teams to prioritize tests for critical and core code first, as illustrated by an e‑commerce checkout bug example.

Misconception 5 – Testing Internal Implementation: Tests should verify expected behavior, not internal structures. Use mocks for dependent objects and centralise test setup in helpers such as createSampleCustomer() . Changing internal implementations should not require test changes.

Misconception 6 – Over‑Emphasising Code Coverage: Coverage is an easy‑to‑measure metric but not a reliable quality indicator. The author introduces CTM (Codepipes Testing Metrics) – PDWT, PBCNT, PTVB, PTD – and suggests a realistic target of around 20% coverage, based on the Pareto principle.

The overall recommendation is to focus on valuable, behavior‑driven tests for critical code rather than chasing high coverage percentages, and to push back against management demands that treat coverage as the sole quality metric.