Add tests for Msg.UpdateReader method

Implemented new tests to validate the Msg.UpdateReader method, ensuring its functionality for both success and failure scenarios. Removed obsolete tests for Msg.NewReader to maintain code clarity and relevance.

msg_test.go

@@ -5741,6 +5741,81 @@ func TestMsg_NewReader(t *testing.T) {
 	})
 }
 
+func TestMsg_UpdateReader(t *testing.T) {
+	t.Run("UpdateReader succeeds", func(t *testing.T) {
+		message := testMessage(t)
+		reader := message.NewReader()
+		if reader == nil {
+			t.Fatalf("failed to create message reader")
+		}
+		if reader.Error() != nil {
+			t.Errorf("failed to create message reader: %s", reader.Error())
+		}
+		message.Subject("This is the actual subject")
+		message.UpdateReader(reader)
+		if reader == nil {
+			t.Fatalf("failed to create message reader")
+		}
+		if reader.Error() != nil {
+			t.Errorf("failed to create message reader: %s", reader.Error())
+		}
+		parsed, err := EMLToMsgFromReader(reader)
+		if err != nil {
+			t.Fatalf("failed to parse message in buffer: %s", err)
+		}
+		checkAddrHeader(t, parsed, HeaderFrom, "WriteTo", 0, 1, TestSenderValid, "")
+		checkAddrHeader(t, parsed, HeaderTo, "WriteTo", 0, 1, TestRcptValid, "")
+		checkGenHeader(t, parsed, HeaderSubject, "WriteTo", 0, 1, "This is the actual subject")
+		parts := parsed.GetParts()
+		if len(parts) != 1 {
+			t.Fatalf("expected 1 parts, got: %d", len(parts))
+		}
+		if parts[0].contentType != TypeTextPlain {
+			t.Errorf("expected contentType to be %s, got: %s", TypeTextPlain, parts[0].contentType)
+		}
+		if parts[0].encoding != EncodingQP {
+			t.Errorf("expected encoding to be %s, got: %s", EncodingQP, parts[0].encoding)
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = parts[0].writeFunc(messageBuf)
+		if err != nil {
+			t.Errorf("writer func failed: %s", err)
+		}
+		got := strings.TrimSpace(messageBuf.String())
+		if !strings.HasSuffix(got, "Testmail") {
+			t.Errorf("expected message buffer to contain Testmail, got: %s", got)
+		}
+	})
+	t.Run("UpdateReader should fail on write", func(t *testing.T) {
+		message := testMessage(t)
+		reader := message.NewReader()
+		if reader == nil {
+			t.Fatalf("failed to create message reader")
+		}
+		if reader.Error() != nil {
+			t.Errorf("failed to create message reader: %s", reader.Error())
+		}
+		message.Subject("This is the actual subject")
+		if len(message.parts) != 1 {
+			t.Fatalf("expected 1 parts, got: %d", len(message.parts))
+		}
+		message.parts[0].writeFunc = func(io.Writer) (int64, error) {
+			return 0, errors.New("intentional write error")
+		}
+		message.UpdateReader(reader)
+		if reader == nil {
+			t.Fatalf("failed to create message reader")
+		}
+		if reader.Error() == nil {
+			t.Fatalf("expected error on write, got nil")
+		}
+		if !strings.EqualFold(reader.Error().Error(), `bodyWriter function: intentional write error`) {
+			t.Errorf("expected error to be %s, got: %s", `bodyWriter function: intentional write error`,
+				reader.Error().Error())
+		}
+	})
+}
+
 /*
 // TestMsg_hasAlt tests the hasAlt() method of the Msg
 
@@ -5775,51 +5850,6 @@ func TestMsg_NewReader(t *testing.T) {
 		}
 	}
 
-// TestMsg_NewReader tests the Msg.NewReader method
-
-	func TestMsg_NewReader(t *testing.T) {
-		m := NewMsg()
-		m.SetBodyString(TypeTextPlain, "TEST123")
-		mr := m.NewReader()
-		if mr == nil {
-			t.Errorf("NewReader failed: Reader is nil")
-		}
-		if mr.Error() != nil {
-			t.Errorf("NewReader failed: %s", mr.Error())
-		}
-	}
-
-// TestMsg_NewReader_ioCopy tests the Msg.NewReader method using io.Copy
-
-	func TestMsg_NewReader_ioCopy(t *testing.T) {
-		wbuf1 := bytes.Buffer{}
-		wbuf2 := bytes.Buffer{}
-		m := NewMsg()
-		m.SetBodyString(TypeTextPlain, "TEST123")
-		mr := m.NewReader()
-		if mr == nil {
-			t.Errorf("NewReader failed: Reader is nil")
-		}
-
-		// First we use WriteTo to have something to compare to
-		_, err := m.WriteTo(&wbuf1)
-		if err != nil {
-			t.Errorf("failed to write body to buffer: %s", err)
-		}
-
-		// Then we write to wbuf2 via io.Copy
-		n, err := io.Copy(&wbuf2, mr)
-		if err != nil {
-			t.Errorf("failed to use io.Copy on Reader: %s", err)
-		}
-		if n != int64(wbuf1.Len()) {
-			t.Errorf("message length of WriteTo and io.Copy differ. Expected: %d, got: %d", wbuf1.Len(), n)
-		}
-		if wbuf1.String() != wbuf2.String() {
-			t.Errorf("message content of WriteTo and io.Copy differ")
-		}
-	}
-
 // TestMsg_UpdateReader tests the Msg.UpdateReader method
 
 	func TestMsg_UpdateReader(t *testing.T) {