fs/asyncreader: skip some tests to work around race detector bug

The race detector currently detects a race with len(chan) against
close(chan).

See: golang/go#27070

Skip the tests which trip this bug under the race detector.

fs/asyncreader/asyncreader_test.go

@@ -13,6 +13,7 @@ import (
 	"testing/iotest"
 	"time"
 
+	"github.com/ncw/rclone/lib/israce"
 	"github.com/ncw/rclone/lib/readers"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -303,6 +304,9 @@ func TestAsyncReaderSkipBytes(t *testing.T) {
 		8000, len(data), BufferSize, 2 * BufferSize}
 
 	for buffers := 1; buffers <= 5; buffers++ {
+		if israce.Enabled && buffers > 1 {
+			t.Skip("FIXME Skipping further tests with race detector until https://github.com/golang/go/issues/27070 is fixed.")
+		}
 		t.Run(fmt.Sprintf("%d", buffers), func(t *testing.T) {
 			for _, initialRead := range initialReads {
 				t.Run(fmt.Sprintf("%d", initialRead), func(t *testing.T) {

lib/israce/israce.go

@@ -0,0 +1,9 @@
+// +build race
+
+// Package israce reports if the Go race detector is enabled.
+//
+// From https://stackoverflow.com/questions/44944959/how-can-i-check-if-the-race-detector-is-enabled-at-runtime
+package israce
+
+// Enabled reports if the race detector is enabled.
+const Enabled = true

lib/israce/norace.go

@@ -0,0 +1,9 @@
+// +build !race
+
+// Package israce reports if the Go race detector is enabled.
+//
+// From https://stackoverflow.com/questions/44944959/how-can-i-check-if-the-race-detector-is-enabled-at-runtime
+package israce
+
+// Enabled reports if the race detector is enabled.
+const Enabled = false