Source: cover.go in package testing

Support for test coverage.


package testing

import (
	"fmt"
	"os"
	"sync/atomic"
)

CoverBlock records the coverage data for a single basic block. The fields are 1-indexed, as in an editor: The opening line of the file is number 1, for example. Columns are measured in bytes. NOTE: This struct is internal to the testing infrastructure and may change. It is not covered (yet) by the Go 1 compatibility guidelines.

type CoverBlock struct {
	Line0 uint32 // Line number for block start.
	Col0  uint16 // Column number for block start.
	Line1 uint32 // Line number for block end.
	Col1  uint16 // Column number for block end.
	Stmts uint16 // Number of statements included in this block.
}

var cover Cover

Cover records information about test coverage checking. NOTE: This struct is internal to the testing infrastructure and may change. It is not covered (yet) by the Go 1 compatibility guidelines.

type Cover struct {
	Mode            string
	Counters        map[string][]uint32
	Blocks          map[string][]CoverBlock
	CoveredPackages string
}

Coverage reports the current code coverage as a fraction in the range [0, 1]. If coverage is not enabled, Coverage returns 0. When running a large set of sequential test cases, checking Coverage after each one can be useful for identifying which test cases exercise new code paths. It is not a replacement for the reports generated by 'go test -cover' and 'go tool cover'.

func Coverage() float64 {
	var n, d int64
	for _, counters := range cover.Counters {
		for i := range counters {
			if atomic.LoadUint32(&counters[i]) > 0 {
				n++
			}
			d++
		}
	}
	if d == 0 {
		return 0
	}
	return float64(n) / float64(d)
}

RegisterCover records the coverage data accumulators for the tests. NOTE: This function is internal to the testing infrastructure and may change. It is not covered (yet) by the Go 1 compatibility guidelines.

func RegisterCover(c Cover) {
	cover = c
}

mustBeNil checks the error and, if present, reports it and exits.

func mustBeNil(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "testing: %s\n", err)
		os.Exit(2)
	}
}

coverReport reports the coverage percentage and writes a coverage profile if requested.

func coverReport() {
	var f *os.File
	var err error
	if *coverProfile != "" {
		f, err = os.Create(toOutputDir(*coverProfile))
		mustBeNil(err)
		fmt.Fprintf(f, "mode: %s\n", cover.Mode)
		defer func() { mustBeNil(f.Close()) }()
	}

	var active, total int64
	var count uint32
	for name, counts := range cover.Counters {
		blocks := cover.Blocks[name]
		for i := range counts {
			stmts := int64(blocks[i].Stmts)
			total += stmts
			count = atomic.LoadUint32(&counts[i]) // For -mode=atomic.
			if count > 0 {
				active += stmts
			}
			if f != nil {
				_, err := fmt.Fprintf(f, "%s:%d.%d,%d.%d %d %d\n", name,
					blocks[i].Line0, blocks[i].Col0,
					blocks[i].Line1, blocks[i].Col1,
					stmts,
					count)
				mustBeNil(err)
			}
		}
	}
	if total == 0 {
		fmt.Println("coverage: [no statements]")
		return
	}
	fmt.Printf("coverage: %.1f%% of statements%s\n", 100*float64(active)/float64(total), cover.CoveredPackages)