fix for empty body codec test

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

codec/codec_test.go

@@ -0,0 +1,46 @@
+package codec_test
+
+import (
+	"testing"
+
+	grpc "github.com/unistack-org/micro-codec-grpc"
+	json "github.com/unistack-org/micro-codec-json"
+	proto "github.com/unistack-org/micro-codec-proto"
+	"github.com/unistack-org/micro/v3/codec"
+)
+
+type testRWC struct{}
+
+func (rwc *testRWC) Read(p []byte) (n int, err error) {
+	return 0, nil
+}
+
+func (rwc *testRWC) Write(p []byte) (n int, err error) {
+	return 0, nil
+}
+
+func (rwc *testRWC) Close() error {
+	return nil
+}
+
+func getCodecs() map[string]codec.Codec {
+	return map[string]codec.Codec{
+		"bytes": codec.NewCodec(),
+		"grpc":  grpc.NewCodec(),
+		"json":  json.NewCodec(),
+		"proto": proto.NewCodec(),
+	}
+}
+
+func Test_WriteEmptyBody(t *testing.T) {
+	rw := &testRWC{}
+	for name, c := range getCodecs() {
+		err := c.Write(rw, &codec.Message{
+			Type:   codec.Error,
+			Header: map[string]string{},
+		}, nil)
+		if err != nil {
+			t.Fatalf("codec %s - expected no error when writing empty/nil body: %s", name, err)
+		}
+	}
+}