Add lockutil test

Verify that the lock works for threads in the same process.

The test fails on windows:

    === RUN   TestWithDirLock
        lockutil_test.go:54: Expected one writer, got [writer 19 writer 0]

(Keeping as separate commit to make it easy to reproduce)

Signed-off-by: Nir Soffer <[email protected]>

Author: nirs

pkg/lockutil/lockutil_test.go

@@ -0,0 +1,56 @@
+package lockutil
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const parallel = 20
+
+func TestWithDirLock(t *testing.T) {
+	dir := t.TempDir()
+	log := filepath.Join(dir, "log")
+
+	errc := make(chan error, 10)
+	for i := 0; i < parallel; i++ {
+		go func() {
+			err := WithDirLock(dir, func() error {
+				if _, err := os.Stat(log); err == nil {
+					return nil
+				} else if !errors.Is(err, os.ErrNotExist) {
+					return err
+				}
+				logFile, err := os.OpenFile(log, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0o640)
+				if err != nil {
+					return err
+				}
+				defer logFile.Close()
+				if _, err := fmt.Fprintf(logFile, "writer %d\n", i); err != nil {
+					return err
+				}
+				return logFile.Close()
+			})
+			errc <- err
+		}()
+	}
+
+	for i := 0; i < parallel; i++ {
+		err := <-errc
+		if err != nil {
+			t.Error(err)
+		}
+	}
+
+	data, err := os.ReadFile(log)
+	if err != nil {
+		t.Fatal(err)
+	}
+	lines := strings.Split(strings.Trim(string(data), "\n"), "\n")
+	if len(lines) != 1 {
+		t.Errorf("Expected one writer, got %v", lines)
+	}
+}