Minor clean-up after #3640 (#3653)

plugin/storage/grpc/README.md

@@ -112,7 +112,9 @@ grpc.Serve(&shared.PluginServices{
 })
 ```
 
-To support writing span via client stream (which can enlarge the throughput), you must fill `StreamingSpanWriter` with the same plugin with `Store` field. Note that use streaming spanWriter may make the `save_by_svr` metric inaccurate, in which case users will need to pay attention to the metrics provided by plugin.
+The plugin framework supports writing spans via gRPC stream, instead of unary messages. Streaming writes can improve throughput and decrease CPU load (see benchmarks in Issue #3636). The plugin needs to implement `StreamingSpanWriter` interface and indicate support via the `streamingSpanWriter` flag in the `Capabilities` response.
+
+Note that using the streaming spanWriter may make the collector's `save_by_svr` metric inaccurate, in which case users will need to pay attention to the metrics provided by the plugin.
 
 Running with a plugin
 ---------------------

plugin/storage/integration/grpc_test.go

@@ -12,6 +12,7 @@
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
+
 //go:build grpc_storage_integration
 // +build grpc_storage_integration
 
@@ -157,11 +158,11 @@ func getPluginFlags(t *testing.T) []string {
 
 func TestGRPCStorage(t *testing.T) {
 	flags := getPluginFlags(t)
-	configPath := os.Getenv("PLUGIN_CONFIG_PATH")
-	if configPath == "" {
+	if configPath := os.Getenv("PLUGIN_CONFIG_PATH"); configPath == "" {
 		t.Log("PLUGIN_CONFIG_PATH env var not set")
+	} else {
+		flags = append(flags, "--grpc-storage-plugin.configuration-file", configPath)
 	}
-	flags = append(flags, "--grpc-storage-plugin.configuration-file", configPath)
 
 	s := &GRPCStorageIntegrationTestSuite{
 		flags: flags,
@@ -174,7 +175,9 @@ func TestGRPCStreamingWriter(t *testing.T) {
 	flags := getPluginFlags(t)
 	wd, err := os.Getwd()
 	require.NoError(t, err)
-	flags = append(flags, "--grpc-storage-plugin.configuration-file", path.Join(wd, streamingPluginConfigPath))
+	flags = append(flags,
+		"--grpc-storage-plugin.configuration-file",
+		path.Join(wd, streamingPluginConfigPath))
 
 	s := &GRPCStorageIntegrationTestSuite{
 		flags: flags,