Revert macro tests to use XCTest

swift-testing is not supported for macro expansion tests yet.
See swiftlang/swift-syntax#2720

Tests/DefaultsMacrosDeclarationsTests/ObservableDefaultMacroTests.swift

@@ -1,6 +1,6 @@
 import SwiftSyntaxMacros
 import SwiftSyntaxMacrosTestSupport
-import Testing
+import XCTest
 
 // Macro implementations build for the host, so the corresponding module is not available when cross-compiling.
 // Cross-compiled tests may still make use of the macro itself in end-to-end tests.
@@ -15,10 +15,9 @@ let testMacros: [String: Macro.Type] = [
 let testMacros: [String: Macro.Type] = [:]
 #endif
 
-@Suite(.serialized)
-final class ObservableDefaultMacroTests {
-	@Test(.disabled(if: testMacros.isEmpty))
+final class ObservableDefaultMacroTests: XCTestCase {
 	func testExpansionWithMemberSyntax() throws {
+		#if canImport(DefaultsMacrosDeclarations)
 		assertMacroExpansion(
 			#"""
 			@Observable
@@ -49,10 +48,13 @@ final class ObservableDefaultMacroTests {
 			macros: testMacros,
 			indentationWidth: .tabs(1)
 		)
+		#else
+		throw XCTSkip("Macros are only supported when running tests for the host platform")
+		#endif
 	}
 
-	@Test(.disabled(if: testMacros.isEmpty))
 	func testExpansionWithDotSyntax() throws {
+		#if canImport(DefaultsMacrosDeclarations)
 		assertMacroExpansion(
 			#"""
 			@Observable
@@ -83,10 +85,13 @@ final class ObservableDefaultMacroTests {
 			macros: testMacros,
 			indentationWidth: .tabs(1)
 		)
+		#else
+		throw XCTSkip("Macros are only supported when running tests for the host platform")
+		#endif
 	}
 
-	@Test(.disabled(if: testMacros.isEmpty))
 	func testExpansionWithFunctionCall() throws {
+		#if canImport(DefaultsMacrosDeclarations)
 		assertMacroExpansion(
 			#"""
 			@Observable
@@ -117,10 +122,13 @@ final class ObservableDefaultMacroTests {
 			macros: testMacros,
 			indentationWidth: .tabs(1)
 		)
+		#else
+		throw XCTSkip("Macros are only supported when running tests for the host platform")
+		#endif
 	}
 
-	@Test(.disabled(if: testMacros.isEmpty))
 	func testExpansionWithProperty() throws {
+		#if canImport(DefaultsMacrosDeclarations)
 		assertMacroExpansion(
 			#"""
 			@Observable
@@ -151,5 +159,8 @@ final class ObservableDefaultMacroTests {
 			macros: testMacros,
 			indentationWidth: .tabs(1)
 		)
+		#else
+		throw XCTSkip("Macros are only supported when running tests for the host platform")
+		#endif
 	}
 }