Migrate BigInt support tests to XCTest

Author: kateinoigakukun

Diff for: IntegrationTests/TestSuites/Sources/PrimaryTests/I64.swift

@@ -914,5 +914,4 @@ try test("JSValueDecoder") {
     try expectEqual(decodedTama.isCat, true)
 }
 
-try testI64()
 Expectation.wait(expectations)

Diff for: IntegrationTests/TestSuites/Sources/PrimaryTests/main.swift

@@ -42,6 +42,10 @@ let package = Package(
             dependencies: ["_CJavaScriptBigIntSupport", "JavaScriptKit"]
         ),
         .target(name: "_CJavaScriptBigIntSupport", dependencies: ["_CJavaScriptKit"]),
+        .testTarget(
+            name: "JavaScriptBigIntSupportTests",
+            dependencies: ["JavaScriptBigIntSupport", "JavaScriptKit"]
+        ),
 
         .target(
             name: "JavaScriptEventLoop",

Diff for: Package.swift

@@ -0,0 +1,50 @@
+import XCTest
+import JavaScriptBigIntSupport
+import JavaScriptKit
+
+class JavaScriptBigIntSupportTests: XCTestCase {
+    func testBigIntSupport() {
+        // Test signed values
+        func testSignedValue(_ value: Int64, file: StaticString = #filePath, line: UInt = #line) {
+            let bigInt = JSBigInt(value)
+            XCTAssertEqual(bigInt.description, value.description, file: file, line: line)
+            let bigInt2 = JSBigInt(_slowBridge: value)
+            XCTAssertEqual(bigInt2.description, value.description, file: file, line: line)
+        }
+        
+        // Test unsigned values
+        func testUnsignedValue(_ value: UInt64, file: StaticString = #filePath, line: UInt = #line) {
+            let bigInt = JSBigInt(unsigned: value)
+            XCTAssertEqual(bigInt.description, value.description, file: file, line: line)
+            let bigInt2 = JSBigInt(_slowBridge: value)
+            XCTAssertEqual(bigInt2.description, value.description, file: file, line: line)
+        }
+        
+        // Test specific signed values
+        testSignedValue(0)
+        testSignedValue(1 << 62)
+        testSignedValue(-2305)
+        
+        // Test random signed values
+        for _ in 0..<100 {
+            testSignedValue(.random(in: .min ... .max))
+        }
+        
+        // Test edge signed values
+        testSignedValue(.min)
+        testSignedValue(.max)
+        
+        // Test specific unsigned values
+        testUnsignedValue(0)
+        testUnsignedValue(1 << 62)
+        testUnsignedValue(1 << 63)
+        testUnsignedValue(.min)
+        testUnsignedValue(.max)
+        testUnsignedValue(~0)
+        
+        // Test random unsigned values
+        for _ in 0..<100 {
+            testUnsignedValue(.random(in: .min ... .max))
+        }
+    }
+}