overallsrace.go

package overallsrace

import "fmt"

func Greeting(who string) string {
	return fmt.Sprintf("Hello %s!", who)
}

overallsrace_cover_atomic.go

package overallsrace

import _cover_atomic_ "sync/atomic"

import "fmt"

func Greeting(who string) string {
	_cover_atomic_.AddUint32(&GoCover.Count[0], 1)
	return fmt.Sprintf("Hello %s!", who)
}

var _ = _cover_atomic_.AddUint32

var GoCover = struct {
	Count     [1]uint32
	Pos       [3 * 1]uint32
	NumStmt   [1]uint16
} {
	Pos: [3 * 1]uint32{
		5, 7, 0x20022, // [0]
	},
	NumStmt: [1]uint16{
		1, // 0
	},
}

overallsrace_cover_count.go

package overallsrace

import "fmt"

func Greeting(who string) string {
	GoCover.Count[0]++
	return fmt.Sprintf("Hello %s!", who)
}

var GoCover = struct {
	Count     [1]uint32
	Pos       [3 * 1]uint32
	NumStmt   [1]uint16
} {
	Pos: [3 * 1]uint32{
		5, 7, 0x20022, // [0]
	},
	NumStmt: [1]uint16{
		1, // 0
	},
}

overallsrace_test.go

package overallsrace

import (
	"sync"
	"testing"
)

func TestGreeting(t *testing.T) {
	var wg sync.WaitGroup

	wg.Add(10)
	for i := 0; i < 10; i++ {
		go func() {
			g := Greeting("World")
			if g != "Hello World!" {
				t.Error("incorrect greeting")
			}
			wg.Done()
		}()
	}

	wg.Wait()
}

report.md

Testing with overalls gives a race

$ overalls -project=github.com/mmcloughlin/overallsrace -- -v -race
| github.com/mmcloughlin/overallsrace
Test args: [test -v -race -covermode=count -coverprofile=profile.coverprofile -outputdir=.../src/github.com/mmcloughlin/overallsrace/ ./.]
2017/04/25 21:33:07 === RUN   TestGreeting
2017/04/25 21:33:07 ==================
2017/04/25 21:33:07 WARNING: DATA RACE
                    ...
2017/04/25 21:33:07 ==================
2017/04/25 21:33:07 --- PASS: TestGreeting (0.00s)
2017/04/25 21:33:07 PASS
2017/04/25 21:33:07 coverage: 100.0% of statements
2017/04/25 21:33:08 Found 1 data race(s)
2017/04/25 21:33:08 exit status 66
2017/04/25 21:33:08 FAIL	github.com/mmcloughlin/overallsrace	1.032s
2017/04/25 21:33:08 ERROR:exit status 1

I believe this is because of -covermode=count

$ go test -v -race -covermode=count
=== RUN   TestGreeting
==================
WARNING: DATA RACE
...
==================
--- PASS: TestGreeting (0.00s)
PASS
coverage: 100.0% of statements
Found 1 data race(s)
exit status 66
FAIL	github.com/mmcloughlin/overallsrace	1.032s

Using atomic removes the race

$ go test -v -race -covermode=atomic
=== RUN   TestGreeting
--- PASS: TestGreeting (0.00s)
PASS
coverage: 100.0% of statements
ok  	github.com/mmcloughlin/overallsrace	1.030s