Coverage measures how much of your code is tested. It matters because it helps identify untested code, guides testing efforts, and ensures critical paths are tested.
Measuring coverage
go test -cover # Show coverage percentage
go test -coverprofile=coverage.out # Generate coverage file
go tool cover -html=coverage.out # View in browserCoverage goals
100% coverage isn't always the goal. Focus on testing critical paths, edge cases, and error conditions. Some code (like simple getters/setters) may not need tests.