The coverage is based on the built in go tooling, which supports line or function based analysis. In addition it can start a webserver where you can browse coverage by file with color output.

    # Generate coverage data
    go test -coverprofile=coverage.out
    
    # View coverage by function
    go tool cover -func="coverage.out"
    
    # View coverage line by line
    go tool cover -html="coverage.out"