Add test for GetAddrHeader with multiple valid addresses

Introduce a new test to validate the behavior of GetAddrHeader for handling multiple addresses (to, cc, bcc). This test ensures that the function correctly processes and returns the expected addresses in various headers.

msg_test.go

@@ -2444,6 +2444,59 @@ func TestMsg_GetAddrHeader(t *testing.T) {
 			})
 		}
 	})
+	t.Run("GetAddrHeader with multiple valid address (to, cc, bcc)", func(t *testing.T) {
+		var fn func(...string) error
+		var addfn func(string) error
+		for _, tt := range addrHeaderTests {
+			message := NewMsg()
+			if message == nil {
+				t.Fatal("message is nil")
+			}
+
+			switch tt.header {
+			case HeaderFrom:
+				continue
+			case HeaderTo:
+				fn = message.To
+				addfn = message.AddTo
+			case HeaderCc:
+				fn = message.Cc
+				addfn = message.AddCc
+			case HeaderBcc:
+				fn = message.Bcc
+				addfn = message.AddBcc
+			default:
+				t.Logf("header %s not supported", tt.header)
+				continue
+			}
+			t.Run(tt.name, func(t *testing.T) {
+				if err := fn("toni.tester@example.com"); err != nil {
+					t.Fatalf("failed to set header: %s", err)
+				}
+				if err := addfn("tina.tester@example.com"); err != nil {
+					t.Fatalf("failed to set additional header value: %s", err)
+				}
+				addrheader := message.GetAddrHeader(tt.header)
+				if len(addrheader) != 2 {
+					t.Errorf("GetAddrHeader: expected 1 address, got: %d", len(addrheader))
+				}
+				if addrheader[0] == nil {
+					t.Fatalf("GetAddrHeader: expected address, got nil")
+				}
+				if addrheader[0].String() != "<toni.tester@example.com>" {
+					t.Errorf("GetAddrHeader: expected address not returned. Want: %s, got: %s",
+						"<toni.tester@example.com>", addrheader[0].String())
+				}
+				if addrheader[1] == nil {
+					t.Fatalf("GetAddrHeader: expected address, got nil")
+				}
+				if addrheader[1].String() != "<tina.tester@example.com>" {
+					t.Errorf("GetAddrHeader: expected address not returned. Want: %s, got: %s",
+						"<tina.tester@example.com>", addrheader[1].String())
+				}
+			})
+		}
+	})
 	t.Run("GetAddrHeader with no addresses", func(t *testing.T) {
 		message := NewMsg()
 		if message == nil {