Q24 of 38 · Test design

What is statement coverage and how does it relate to test design?

Test designJuniortest-designcoveragestatement-coveragebranch-coveragestructural-testing

Short answer

Short answer: Statement coverage measures the percentage of executable statements exercised by your tests. As a test design concept, it tells you which code paths have never been tested — not whether the tests are good, but where the gaps are.

Detail

Statement coverage (also called line coverage) is the simplest structural coverage metric: every executable line that is reached by at least one test contributes to the percentage. 100% statement coverage means every line ran, but it does not mean every outcome was verified.

Branch coverage is stricter: every decision point (if/else, switch, ternary) must have its true and false branches both exercised. A test suite can achieve 100% statement coverage with 0% branch coverage if every if-block happens to evaluate true in every test.

At the design level, coverage metrics are gap-finding tools. Use them to identify which logical branches have no corresponding test case, then write tests that target those branches intentionally — not to inflate the percentage mechanically.

// WHAT INTERVIEWERS LOOK FOR

Knowing the difference between statement and branch coverage. Understanding coverage as a gap-finding tool, not a quality target. Not confusing high coverage with good tests.

// Related questions

How do you approach branch coverage for a complex conditional logic block?

Test design