diff --git a/protocol/nats_jetstream/v3/protocol_test.go b/protocol/nats_jetstream/v3/protocol_test.go
new file mode 100644
index 0000000..b857a94
--- /dev/null
+++ b/protocol/nats_jetstream/v3/protocol_test.go
@@ -0,0 +1,85 @@
+/*
+ Copyright 2024 The CloudEvents Authors
+ SPDX-License-Identifier: Apache-2.0
+*/
+
+package nats_jetstream
+
+import (
+	"context"
+	"testing"
+
+	"github.com/cloudevents/sdk-go/v2/test"
+	"github.com/nats-io/nats.go"
+	"github.com/nats-io/nats.go/jetstream"
+)
+
+// mockJetStream implements jetstream.JetStream interface for testing
+type mockJetStream struct {
+	streamNameBySubjectFunc func(ctx context.Context, subject string) (string, error)
+	publishMsgFunc          func(ctx context.Context, msg *nats.Msg, opts ...jetstream.PublishOpt) (*jetstream.PubAck, error)
+	jetstream.JetStream
+}
+
+func (m *mockJetStream) StreamNameBySubject(ctx context.Context, subject string) (string, error) {
+	return m.streamNameBySubjectFunc(ctx, subject)
+}
+
+func (m *mockJetStream) PublishMsg(ctx context.Context, msg *nats.Msg, opts ...jetstream.PublishOpt) (*jetstream.PubAck, error) {
+	return m.publishMsgFunc(ctx, msg, opts...)
+}
+
+func TestSend(t *testing.T) {
+	tests := []struct {
+		name        string
+		sendSubject string
+		ctx         context.Context
+		wantSubject string
+	}{
+		{
+			name:        "using p.sendSubject",
+			sendSubject: "test.subject",
+			ctx:         context.Background(),
+			wantSubject: "test.subject",
+		},
+		{
+			name:        "using WithSubject",
+			sendSubject: "",
+			ctx:         WithSubject(context.Background(), "test.ctxSubject"),
+			wantSubject: "test.ctxSubject",
+		},
+		{
+			name:        "using WithSubject and p.sendSubject",
+			sendSubject: "test.subject",
+			ctx:         WithSubject(context.Background(), "test.ctxSubject"),
+			wantSubject: "test.ctxSubject",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockJS := &mockJetStream{
+				streamNameBySubjectFunc: func(ctx context.Context, subject string) (string, error) {
+					if subject != tt.wantSubject {
+						t.Errorf("unexpected subject: got %s, want %s", subject, tt.wantSubject)
+					}
+					return "test-stream", nil
+				},
+				publishMsgFunc: func(ctx context.Context, msg *nats.Msg, opts ...jetstream.PublishOpt) (*jetstream.PubAck, error) {
+					if msg.Subject != tt.wantSubject {
+						t.Errorf("unexpected subject in publish: got %s, want %s", msg.Subject, tt.wantSubject)
+					}
+					return nil, nil
+				},
+			}
+
+			p := &Protocol{
+				jetStream:   mockJS,
+				sendSubject: tt.sendSubject,
+			}
+
+			msg := test.FullMessage()
+			_ = p.Send(tt.ctx, msg)
+		})
+	}
+}