diff --git a/metadapta_test.go b/metadapta_test.go
index c4c8f9b..cb39859 100644
--- a/metadapta_test.go
+++ b/metadapta_test.go
@@ -1,6 +1,8 @@
 package hopp
 
+import "io"
 import "bytes"
+import "errors"
 import "slices"
 import "testing"
 
@@ -25,3 +27,42 @@ func TestDecodeMessageA(test *testing.T) {
 		test.Fatalf("not equal: %v %v", got, correct)
 	}
 }
+
+func TestDecodeMessageAErr(test *testing.T) {
+	_, _, _, err := decodeMessageA(bytes.NewReader([]byte {
+		0x58, 0x00, 0xFE, 0xAB, 0xC3, 0x10, 0x4F, 0x04,
+		0x6B, 0x12,
+		0x01, 0x06,
+		0x00, 0x01, 0x02, 0x03, 0x04, 0x05,
+	}))
+	if !errors.Is(err, io.ErrUnexpectedEOF) {
+		test.Fatalf("wrong error: %v", err)
+	}
+}
+
+func TestEncodeMessageA(test *testing.T) {
+	buffer := new(bytes.Buffer)
+	payload := []byte { 0x00, 0x01, 0x02, 0x03, 0x04, 0x05 }
+	err := encodeMessageA(buffer, 0x5800FEABC3104F04, 0x6B12, payload)
+	correct := []byte {
+		0x58, 0x00, 0xFE, 0xAB, 0xC3, 0x10, 0x4F, 0x04,
+		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 TestEncodeMessageAErr(test *testing.T) {
+	buffer := new(bytes.Buffer)
+	payload := make([]byte, 0x10000)
+	err := encodeMessageA(buffer, 0x5800FEABC3104F04, 0x6B12, payload)
+	if !errors.Is(err, ErrPayloadTooLarge) {
+		test.Fatalf("wrong error: %v", err)
+	}
+}