Add tests for Msg_GetAddrHeader

Introduce unit tests for the GetAddrHeader function in the Msg struct. These tests cover various scenarios, including valid addresses and handling of headers like "from," "to," "cc," and "bcc."

msg_test.go

@@ -2384,6 +2384,82 @@ func TestMsg_GetRecipients(t *testing.T) {
 	})
 }
 
+func TestMsg_GetAddrHeader(t *testing.T) {
+	t.Run("GetAddrHeader with valid address (from)", func(t *testing.T) {
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		if err := message.From("toni.tester@example.com"); err != nil {
+			t.Fatalf("failed to set header: %s", err)
+		}
+		addrheader := message.GetAddrHeader(HeaderFrom)
+		if len(addrheader) != 1 {
+			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())
+		}
+	})
+	t.Run("GetAddrHeader with valid address (to, cc, bcc)", func(t *testing.T) {
+		var fn 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
+			case HeaderCc:
+				fn = message.Cc
+			case HeaderBcc:
+				fn = message.Bcc
+			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)
+				}
+				addrheader := message.GetAddrHeader(tt.header)
+				if len(addrheader) != 1 {
+					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())
+				}
+			})
+		}
+	})
+	t.Run("GetAddrHeader with no addresses", func(t *testing.T) {
+		message := NewMsg()
+		if message == nil {
+			t.Fatal("message is nil")
+		}
+		for _, tt := range addrHeaderTests {
+			t.Run(tt.name, func(t *testing.T) {
+				addrheader := message.GetAddrHeader(HeaderFrom)
+				if len(addrheader) != 0 {
+					t.Errorf("GetAddrHeader: expected 0 address, got: %d", len(addrheader))
+				}
+			})
+		}
+	})
+}
+
 // checkAddrHeader verifies the correctness of an AddrHeader in a Msg based on the provided criteria.
 // It checks whether the AddrHeader contains the correct address, name, and number of fields.
 func checkAddrHeader(t *testing.T, message *Msg, header AddrHeader, fn string, field, wantFields int,