diff --git a/metadaptb_test.go b/metadaptb_test.go
new file mode 100644
index 0000000..416f5fd
--- /dev/null
+++ b/metadaptb_test.go
@@ -0,0 +1,62 @@
+package hopp
+
+import "io"
+import "bytes"
+import "errors"
+import "slices"
+import "testing"
+
+func TestEncodeMessageB(test *testing.T) {
+	buffer := new(bytes.Buffer)
+	payload := []byte { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 }
+	err := encodeMessageB(buffer, 0x6B12, payload)
+	correct := []byte {
+		0x6B, 0x12,
+		0x00, 0x06,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+	}
+	if err != nil {
+		test.Fatal(err)
+	}
+	if got, correct := buffer.Bytes(), correct; !slices.Equal(got, correct) {
+		test.Fatalf("not equal: %v %v", got, correct)
+	}
+}
+
+func TestEncodeMessageBErr(test *testing.T) {
+	buffer := new(bytes.Buffer)
+	payload := make([]byte, 0x10000)
+	err := encodeMessageB(buffer, 0x6B12, payload)
+	if !errors.Is(err, ErrPayloadTooLarge) {
+		test.Fatalf("wrong error: %v", err)
+	}
+}
+
+func TestDecodeMessageB(test *testing.T) {
+	method, payload, err := decodeMessageB(bytes.NewReader([]byte {
+		0x6B, 0x12,
+		0x00, 0x06,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+	}))
+	if err != nil {
+		test.Fatal(err)
+	}
+	if got, correct := method, uint16(0x6B12); got != correct {
+		test.Fatalf("not equal: %v %v", got, correct)
+	}
+	correctPayload := []byte { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 }
+	if got, correct := payload, correctPayload; !slices.Equal(got, correct) {
+		test.Fatalf("not equal: %v %v", got, correct)
+	}
+}
+
+func TestDecodeMessageBErr(test *testing.T) {
+	_, _, err := decodeMessageB(bytes.NewReader([]byte {
+		0x6B, 0x12,
+		0x01, 0x06,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+	}))
+	if !errors.Is(err, io.ErrUnexpectedEOF) {
+		test.Fatalf("wrong error: %v", err)
+	}
+}