Beyond %: a practical guide to coverage metrics (and when to ignore them)

Code coverage is deceptively simple — until you try to make decisions from it. This talk explains the main metrics — line, statement, branch, and path coverage — shows how each can mislead, and explains when raising the percentage no longer raises quality. We will use small, clear examples to expose common coverage illusions (green lines and rising percentages that do not add test quality), show how cyclomatic complexity can bound the minimum number of tests you need (and when it does not), and discuss mutation testing as a complementary technique and its practical limitations. You will learn how to spot the saturation zone where chasing extra percent stops paying off, and how to set sensible gates that reward real defect-finding rather than vanity targets.
Key takeaways
• What line, branch, and path coverage actually measure, and their blind spots
• How cyclomatic complexity relates to required test cases (and when it does not)
• Practical tips for reading and interpreting coverage reports
• The trade-off between measurement precision and practical usability
• Why saturation happens and why setting meaningful coverage gates is hard
Target audience
Engineers, SDETs, and tech leads who own tests or quality gates and want actionable guidance beyond a single number.