Code Coverage Calculator

The four standard coverage types are: Lines (percentage of source lines executed), Functions (percentage of functions/methods called), Branches (percentage of decision branches taken — e.g. both true and false sides of an if statement), and Statements (percentage of individual statements executed). Branch coverage is generally the strictest and most meaningful measure of test thoroughness.

80% is the widely accepted industry standard for most production projects. Google's engineering practices recommend 60% as acceptable, 75% as good, and 90%+ as exemplary. However, raw coverage percentages can be misleading — 100% line coverage does not mean your tests verify the correct behavior. Focus on meaningful assertions alongside coverage targets.

Add a coverageThreshold block to your jest.config.js or vitest.config.ts under the coverage key. Set global thresholds for lines, functions, branches, and statements as percentages (0–100). When running with --coverage, Jest/Vitest will fail the run if any metric falls below the configured threshold — perfect for CI enforcement.

Line coverage counts whether a line was executed at least once. Branch coverage checks whether every logical path was taken — for example, both the true and false branches of an if/else. A line can be 'covered' even if only one branch was tested, so branch coverage catches gaps that line coverage misses. Always aim to meet both thresholds.

Common causes: (1) Your jest.config.js has a coverageThreshold that one metric falls below. (2) You are running coverage on a different set of files locally vs CI (check collectCoverageFrom). (3) A new file was added without tests, which reduces overall percentages. (4) You're comparing v8 vs babel coverage providers, which count differently. Run jest --coverage --verbose locally to match CI exactly.

No. 100% coverage means every line was executed during tests, but it says nothing about whether those tests actually assert correct behavior. You can achieve 100% coverage with tests that never check any output. Coverage is a floor, not a ceiling — combine it with meaningful assertions, property-based testing, and integration tests for real confidence.