Source watcher ErrStoppedWatcher and fixed test

config/source/env/env_test.go

@@ -86,8 +86,8 @@ func TestEnvvar_Prefixes(t *testing.T) {
 }
 
 func TestEnvvar_WatchNextNoOpsUntilStop(t *testing.T) {
-	source := NewSource(WithStrippedPrefix("GOMICRO_"))
-	w, err := source.Watch()
+	src := NewSource(WithStrippedPrefix("GOMICRO_"))
+	w, err := src.Watch()
 	if err != nil {
 		t.Error(err)
 	}
@@ -97,7 +97,7 @@ func TestEnvvar_WatchNextNoOpsUntilStop(t *testing.T) {
 		w.Stop()
 	}()
 
-	if _, err := w.Next(); err.Error() != "watcher stopped" {
+	if _, err := w.Next(); err != source.ErrWatcherStopped {
 		t.Errorf("expected watcher stopped error, got %v", err)
 	}
 }

config/source/env/watcher.go

@@ -1,8 +1,6 @@
 package env
 
 import (
-	"errors"
-
 	"github.com/micro/go-micro/config/source"
 )
 
@@ -13,7 +11,7 @@ type watcher struct {
 func (w *watcher) Next() (*source.ChangeSet, error) {
 	<-w.exit
 
-	return nil, errors.New("watcher stopped")
+	return nil, source.ErrWatcherStopped
 }
 
 func (w *watcher) Stop() error {