newcover.go

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Support for test coverage with redesigned coverage implementation.
     6  
     7  package testing
     8  
     9  import (
    10  	"fmt"
    11  	"os"
    12  	_ "unsafe" // for linkname
    13  )
    14  
    15  // cover variable stores the current coverage mode and a
    16  // tear-down function to be called at the end of the testing run.
    17  var cover struct {
    18  	mode        string
    19  	tearDown    func(coverprofile string, gocoverdir string) (string, error)
    20  	snapshotcov func() float64
    21  }
    22  
    23  // registerCover is invoked during "go test -cover" runs.
    24  // It is used to record a 'tear down' function
    25  // (to be called when the test is complete) and the coverage mode.
    26  func registerCover(mode string, tearDown func(coverprofile string, gocoverdir string) (string, error), snapcov func() float64) {
    27  	if mode == "" {
    28  		return
    29  	}
    30  	cover.mode = mode
    31  	cover.tearDown = tearDown
    32  	cover.snapshotcov = snapcov
    33  }
    34  
    35  // coverReport reports the coverage percentage and
    36  // writes a coverage profile if requested.
    37  // This invokes a callback in _testmain.go that will
    38  // emit coverage data at the point where test execution is complete,
    39  // for "go test -cover" runs.
    40  func coverReport() {
    41  	if errmsg, err := cover.tearDown(*coverProfile, *gocoverdir); err != nil {
    42  		fmt.Fprintf(os.Stderr, "%s: %v\n", errmsg, err)
    43  		os.Exit(2)
    44  	}
    45  }
    46  
    47  // Coverage reports the current code coverage as a fraction in the range [0, 1].
    48  // If coverage is not enabled, Coverage returns 0.
    49  //
    50  // When running a large set of sequential test cases, checking Coverage after each one
    51  // can be useful for identifying which test cases exercise new code paths.
    52  // It is not a replacement for the reports generated by 'go test -cover' and
    53  // 'go tool cover'.
    54  func Coverage() float64 {
    55  	if cover.mode == "" {
    56  		return 0.0
    57  	}
    58  	return cover.snapshotcov()
    59  }
    60
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