test(dnsserver): improve core/dnsserver test coverage (#7317)

Add comprehensive tests for multiple components including server blocks
inspection, configuration handling, DoH/DoQ writers, and server startup
functions. Increases overall test coverage from 27% to 38.4% with
particular focus on register.go, https.go, quic.go, and config.go.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

core/dnsserver/onstartup_test.go

@@ -37,3 +37,110 @@ func TestRegex1035PrefSyntax(t *testing.T) {
 		}
 	}
 }
+
+func TestStartUpZones(t *testing.T) {
+	tests := []struct {
+		name           string
+		protocol       string
+		addr           string
+		zones          map[string][]*Config
+		expectedOutput string
+	}{
+		{
+			name:           "no zones",
+			protocol:       "dns://",
+			addr:           "127.0.0.1:53",
+			zones:          map[string][]*Config{},
+			expectedOutput: "",
+		},
+		{
+			name:           "single zone valid syntax ip and port",
+			protocol:       "dns://",
+			addr:           "127.0.0.1:53",
+			zones:          map[string][]*Config{"example.com.": nil},
+			expectedOutput: "dns://example.com.:53 on 127.0.0.1\n",
+		},
+		{
+			name:           "single zone valid syntax port only",
+			protocol:       "http://",
+			addr:           ":8080",
+			zones:          map[string][]*Config{"example.org.": nil},
+			expectedOutput: "http://example.org.:8080\n",
+		},
+		{
+			name:     "single zone invalid syntax",
+			protocol: "tls://",
+			addr:     "10.0.0.1:853",
+			zones:    map[string][]*Config{"invalid-zone": nil},
+			expectedOutput: "Warning: Domain \"invalid-zone\" does not follow RFC1035 preferred syntax\n" +
+				"tls://invalid-zone:853 on 10.0.0.1\n",
+		},
+		{
+			name:     "multiple zones sorted order",
+			protocol: "dns://",
+			addr:     "localhost:5353",
+			zones: map[string][]*Config{
+				"c-zone.com.": nil,
+				"a-zone.org.": nil,
+				"b-zone.net.": nil,
+			},
+			expectedOutput: "dns://a-zone.org.:5353 on localhost\n" +
+				"dns://b-zone.net.:5353 on localhost\n" +
+				"dns://c-zone.com.:5353 on localhost\n",
+		},
+		{
+			name:           "addr parse error",
+			protocol:       "grpc://",
+			addr:           "[::1]:8080:extra", // Malformed, should cause SplitProtocolHostPort to error
+			zones:          map[string][]*Config{"error.example.": nil},
+			expectedOutput: "grpc://error.example.:[::1]:8080:extra\n",
+		},
+		{
+			name:           "root zone",
+			protocol:       "dns://",
+			addr:           "192.168.1.1:53",
+			zones:          map[string][]*Config{".": nil},
+			expectedOutput: "dns://.:53 on 192.168.1.1\n",
+		},
+		{
+			name:           "reverse zone",
+			protocol:       "dns://",
+			addr:           ":53",
+			zones:          map[string][]*Config{"1.0.168.192.in-addr.arpa.": nil},
+			expectedOutput: "dns://1.0.168.192.in-addr.arpa.:53\n",
+		},
+		{
+			name:     "multiple zones mixed syntax and addr handling",
+			protocol: "quic://",
+			addr:     "coolserver.local:784",
+			zones: map[string][]*Config{
+				"valid.net.":         nil,
+				"_tcp.service.":      nil, // Invalid syntax
+				"another.valid.com.": nil,
+			},
+			expectedOutput: "Warning: Domain \"_tcp.service.\" does not follow RFC1035 preferred syntax\n" +
+				"quic://_tcp.service.:784 on coolserver.local\n" +
+				"quic://another.valid.com.:784 on coolserver.local\n" +
+				"quic://valid.net.:784 on coolserver.local\n",
+		},
+		{
+			name:     "zone with leading dash invalid",
+			protocol: "dns://",
+			addr:     "127.0.0.1:53",
+			zones:    map[string][]*Config{"-leadingdash.com.": nil},
+			expectedOutput: "Warning: Domain \"-leadingdash.com.\" does not follow RFC1035 preferred syntax\n" +
+				"dns://-leadingdash.com.:53 on 127.0.0.1\n",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			got := startUpZones(tc.protocol, tc.addr, tc.zones)
+			if got != tc.expectedOutput {
+				// Use %q for expected and got to make differences in whitespace/newlines visible.
+				t.Errorf("startUpZones(%q, %q, ...) mismatch for test '%s':\nGot:\n%q\nExpected:\n%q",
+					tc.protocol, tc.addr, tc.name, got, tc.expectedOutput)
+			}
+		})
+	}
+}