diff --git a/Package.swift b/Package.swift
index ac0f503..c5770a2 100644
--- a/Package.swift
+++ b/Package.swift
@@ -1,49 +1,46 @@
-// swift-tools-version:6.4
+// swift-tools-version:5.5
 import PackageDescription
 
 let package = Package(
     name: "JavaScriptCore",
-    platforms: [
-        .macOS(.v26),
-    ],
     products: [
         .library(
             name: "SJavaScriptCore",
-            targets: ["SJavaScriptCore"]
-        ),
+            targets: ["SJavaScriptCore"]),
     ],
     dependencies: [
         .package(name: "JavaScript"),
+        .package(name: "Test"),
     ],
     targets: [
         .target(
-            name: "SJavaScriptCore",
-            dependencies: [
-                .target(
-                    name: "CJavaScriptCore",
-                    condition: .when(platforms: [.linux])
-                ),
-                .product(
-                    name: "JavaScript",
-                    package: "javascript"
-                ),
-            ],
-            path: "./Sources/JavaScriptCore"
-        ),
-        .systemLibrary(
             name: "CJavaScriptCore",
-            pkgConfig: "javascriptcoregtk-4.1",
-            providers: [.aptItem(["libjavascriptcoregtk-4.1-dev"])]
-        ),
-        .testTarget(
-            name: "Tests",
-            dependencies: [
-                "SJavaScriptCore"
-            ]
-        )
+            dependencies: []),
+        .target(
+            name: "SJavaScriptCore",
+            dependencies: ["CJavaScriptCore", "JavaScript"])
     ]
 )
 
+// MARK: - tests
+
+testTarget("SJavaScriptCore") { test in
+    test("JavaScript")
+    test("JSValue")
+}
+
+func testTarget(_ target: String, task: ((String) -> Void) -> Void) {
+    task { test in addTest(target: target, name: test) }
+}
+
+func addTest(target: String, name: String) {
+    package.targets.append(
+        .executableTarget(
+            name: "Tests/\(target)/\(name)",
+            dependencies: ["Test", "SJavaScriptCore"],
+            path: "Tests/\(target)/\(name)"))
+}
+
 // MARK: - custom package source
 
 #if canImport(ObjectiveC)
@@ -60,7 +57,7 @@ extension Package.Dependency {
 
         var baseUrl: String {
             switch self {
-            case .local: return "../../swiftstack/"
+            case .local: return "../"
             case .remote: return "https://swiftstack.io/"
             case .github: return "https://github.com/swiftstack/"
             }
@@ -86,6 +83,6 @@ extension Package.Dependency {
     static func package(name: String, source: Source) -> Package.Dependency {
         return source == .local
             ? .package(name: name, path: source.url(for: name))
-            : .package(url: source.url(for: name), branch: "dev")
+            : .package(name: name, url: source.url(for: name), .branch("dev"))
     }
 }
diff --git a/README.md b/README.md
index 95fa1c9..5179f60 100644
--- a/README.md
+++ b/README.md
@@ -30,5 +30,7 @@ Just works
 ### Linux
 
 ```bash
-apt install -y libjavascriptcoregtk-4.1-dev
+apt install -y libjavascriptcoregtk-4.0-dev
+swift build -Xcc -I/usr/include/webkitgtk-4.0
+swift test -Xcc -I/usr/include/webkitgtk-4.0
 ```
diff --git a/Sources/CJavaScriptCore/blank.c b/Sources/CJavaScriptCore/blank.c
new file mode 100644
index 0000000..e69de29
diff --git a/Sources/CJavaScriptCore/include/include.h b/Sources/CJavaScriptCore/include/include.h
new file mode 100644
index 0000000..2f77237
--- /dev/null
+++ b/Sources/CJavaScriptCore/include/include.h
@@ -0,0 +1,7 @@
+
+#ifndef __JAVASCRIPTCORE_H__
+#define __JAVASCRIPTCORE_H__
+
+#include <JavaScriptCore/JavaScript.h>
+
+#endif
diff --git a/Sources/CJavaScriptCore/include/module.modulemap b/Sources/CJavaScriptCore/include/module.modulemap
new file mode 100644
index 0000000..88dda56
--- /dev/null
+++ b/Sources/CJavaScriptCore/include/module.modulemap
@@ -0,0 +1,6 @@
+
+module CJavaScriptCore [system] {
+    header "include.h"
+    link "javascriptcoregtk-4.0"
+    export *
+}
diff --git a/Sources/CJavaScriptCore/module.modulemap b/Sources/CJavaScriptCore/module.modulemap
deleted file mode 100644
index 654928b..0000000
--- a/Sources/CJavaScriptCore/module.modulemap
+++ /dev/null
@@ -1,5 +0,0 @@
-module CJavaScriptCore [system] {
-    header "/usr/include/webkitgtk-4.1/JavaScriptCore/JavaScript.h"
-    link "javascriptcoregtk-4.1"
-    export *
-}
diff --git a/Sources/JavaScriptCore/JSContext+closure.swift b/Sources/SJavaScriptCore/JSContext+closure.swift
similarity index 68%
rename from Sources/JavaScriptCore/JSContext+closure.swift
rename to Sources/SJavaScriptCore/JSContext+closure.swift
index 2957649..44bd883 100644
--- a/Sources/JavaScriptCore/JSContext+closure.swift
+++ b/Sources/SJavaScriptCore/JSContext+closure.swift
@@ -1,37 +1,31 @@
+
 #if os(Linux)
 import CJavaScriptCore
 #else
 import JavaScriptCore
 #endif
 
-import Synchronization
-
 @_exported import JavaScript
 
-private
-let functions: Mutex<[OpaquePointer: ([JSValue]) throws -> Value]> = .init([:])
-
-extension JSObjectRef: @unchecked @retroactive Sendable {}
+private var functions: [OpaquePointer: ([JSValue]) throws -> Value] = [:]
 
 extension JSContext {
     public func createFunction(
         name: String,
-        _ body: @escaping @Sendable ([JSValue]) throws -> Value
-    ) throws {
+        _ body: @escaping ([JSValue]) throws -> Value) throws
+    {
         let function = try createFunction(name: name, callback: wrapper)
-        functions.withLock { $0[function] = body }
+        functions[function] = body
     }
 
     public func createFunction(
         name: String,
-        _ body: @escaping @Sendable ([JSValue]) throws -> Void
-    ) throws {
+        _ body: @escaping ([JSValue]) throws -> Void) throws
+    {
         let function = try createFunction(name: name, callback: wrapper)
-        functions.withLock {
-            $0[function] = { arguments in
-                try body(arguments)
-                return .undefined
-            }
+        functions[function] = { arguments in
+            try body(arguments)
+            return .undefined
         }
     }
 }
@@ -39,8 +33,8 @@ extension JSContext {
 extension JSContext {
     public func createFunction(
         name: String,
-        _ body: @escaping @Sendable () throws -> Value
-    ) throws {
+        _ body: @escaping () throws -> Value) throws
+    {
         return try createFunction(name: name) { _ in
             return try body()
         }
@@ -48,8 +42,8 @@ extension JSContext {
 
     public func createFunction(
         name: String,
-        _ body: @escaping @Sendable () throws -> Void
-    ) throws {
+        _ body: @escaping () throws -> Void) throws
+    {
         try createFunction(name: name) { _ in
             try body()
         }
@@ -62,9 +56,9 @@ func wrapper(
     thisObject: JSObjectRef!,
     argumentCount: Int,
     arguments: UnsafePointer<JSValueRef?>?,
-    exception: UnsafeMutablePointer<JSValueRef?>?
-) -> JSValueRef? {
-    guard let body = functions.withLock({ $0[function] }) else {
+    exception: UnsafeMutablePointer<JSValueRef?>?) -> JSValueRef?
+{
+    guard let body = functions[function] else {
         if let exception = exception {
             let error = "swift error: unregistered function"
             exception.pointee = JSValue(string: error, in: ctx).pointer
diff --git a/Sources/JavaScriptCore/JSContext.swift b/Sources/SJavaScriptCore/JSContext.swift
similarity index 97%
rename from Sources/JavaScriptCore/JSContext.swift
rename to Sources/SJavaScriptCore/JSContext.swift
index 47e5872..964e449 100644
--- a/Sources/JavaScriptCore/JSContext.swift
+++ b/Sources/SJavaScriptCore/JSContext.swift
@@ -1,3 +1,4 @@
+
 #if os(Linux)
 import CJavaScriptCore
 #else
@@ -7,7 +8,7 @@ import JavaScriptCore
 public class JSContext {
     let group: JSContextGroupRef
     let context: JSGlobalContextRef
-    var exception: JSObjectRef?
+    var exception: JSObjectRef? = nil
 
     var global: JSObjectRef {
         return JSContextGetGlobalObject(context)!
diff --git a/Sources/JavaScriptCore/JSError.swift b/Sources/SJavaScriptCore/JSError.swift
similarity index 99%
rename from Sources/JavaScriptCore/JSError.swift
rename to Sources/SJavaScriptCore/JSError.swift
index 09cda29..ee8e9e8 100644
--- a/Sources/JavaScriptCore/JSError.swift
+++ b/Sources/SJavaScriptCore/JSError.swift
@@ -1,3 +1,4 @@
+
 #if os(Linux)
 import CJavaScriptCore
 #else
diff --git a/Sources/JavaScriptCore/JSValue.swift b/Sources/SJavaScriptCore/JSValue.swift
similarity index 98%
rename from Sources/JavaScriptCore/JSValue.swift
rename to Sources/SJavaScriptCore/JSValue.swift
index cf95f16..a94a045 100644
--- a/Sources/JavaScriptCore/JSValue.swift
+++ b/Sources/SJavaScriptCore/JSValue.swift
@@ -1,3 +1,4 @@
+
 #if os(Linux)
 import CJavaScriptCore
 #else
@@ -78,7 +79,7 @@ extension JSValue {
         let property = JSStringCreateWithCharacters(bytes, bytes.count)
         defer { JSStringRelease(property) }
 
-        var exception: JSValueRef?
+        var exception: JSValueRef? = nil
         let result = JSObjectGetProperty(context, pointer, property, &exception)
 
         if exception != nil {
@@ -88,6 +89,7 @@ extension JSValue {
     }
 }
 
+
 extension JSValue {
     public var isNull: Bool {
         return JSValueIsNull(context, pointer)
diff --git a/Sources/JavaScriptCore/shims.swift b/Sources/SJavaScriptCore/shims.swift
similarity index 72%
rename from Sources/JavaScriptCore/shims.swift
rename to Sources/SJavaScriptCore/shims.swift
index 2418ab5..909cdd5 100644
--- a/Sources/JavaScriptCore/shims.swift
+++ b/Sources/SJavaScriptCore/shims.swift
@@ -1,3 +1,4 @@
+
 #if os(Linux)
 import CJavaScriptCore
 #else
@@ -8,7 +9,7 @@ public func JSValueToStringCopy(
     _ ctx: JSContextRef,
     _ value: JSValueRef
 ) throws -> JSStringRef {
-    var exception: JSValueRef?
+    var exception: JSValueRef? = nil
     let result = JSValueToStringCopy(ctx, value, &exception)
     if let exception = exception {
         throw JSError(context: ctx, pointer: exception)
@@ -20,7 +21,7 @@ public func JSValueToNumber(
     _ ctx: JSContextRef,
     _ value: JSValueRef
 ) throws -> Double {
-    var exception: JSValueRef?
+    var exception: JSValueRef? = nil
     let result = JSValueToNumber(ctx, value, &exception)
     if let exception = exception {
         throw JSError(context: ctx, pointer: exception)
@@ -36,7 +37,7 @@ public func JSEvaluateScript(
     _ sourceURL: JSStringRef!,
     _ startingLineNumber: Int32
 ) throws -> JSValueRef {
-    var exception: JSValueRef?
+    var exception: JSValueRef? = nil
     let result = JSEvaluateScript(
         ctx, script, thisObject, sourceURL, startingLineNumber, &exception)
     if let exception = exception {
@@ -46,7 +47,7 @@ public func JSEvaluateScript(
     return result!
 }
 
-public struct JSPropertyAttributes: OptionSet, Sendable {
+public struct JSPropertyAttributes: OptionSet {
     public let rawValue: UInt32
 
     public init(rawValue: UInt32) {
@@ -54,18 +55,13 @@ public struct JSPropertyAttributes: OptionSet, Sendable {
     }
 
     /// Specifies that a property has no special attributes.
-    static let none = JSPropertyAttributes(
-        rawValue: UInt32(kJSPropertyAttributeNone))
+    static let none = JSPropertyAttributes(rawValue: UInt32(kJSPropertyAttributeNone))
     /// Specifies that a property is read-only.
-    static let readOnly = JSPropertyAttributes(
-        rawValue: UInt32(kJSPropertyAttributeNone))
-    /// Specifies that a property should not be enumerated by
-    /// JSPropertyEnumerators and JavaScript for...in loops.
-    static let dontEnum = JSPropertyAttributes(
-        rawValue: UInt32(kJSPropertyAttributeNone))
+    static let readOnly = JSPropertyAttributes(rawValue: UInt32(kJSPropertyAttributeNone))
+    /// Specifies that a property should not be enumerated by JSPropertyEnumerators and JavaScript for...in loops.
+    static let dontEnum = JSPropertyAttributes(rawValue: UInt32(kJSPropertyAttributeNone))
     /// Specifies that the delete operation should fail on a property.
-    static let dontDelete = JSPropertyAttributes(
-        rawValue: UInt32(kJSPropertyAttributeNone))
+    static let dontDelete = JSPropertyAttributes(rawValue: UInt32(kJSPropertyAttributeNone))
 }
 
 public func JSObjectSetProperty(
@@ -75,7 +71,7 @@ public func JSObjectSetProperty(
     _ value: JSValueRef!,
     _ attributes: JSPropertyAttributes
 ) throws {
-    var exception: JSValueRef?
+    var exception: JSValueRef? = nil
     JSObjectSetProperty(
         ctx, object, propertyName, value, attributes.rawValue, &exception)
     if let exception = exception {
diff --git a/Tests/SJavaScriptCore/JSValue.swift b/Tests/SJavaScriptCore/JSValue.swift
deleted file mode 100644
index 9045f01..0000000
--- a/Tests/SJavaScriptCore/JSValue.swift
+++ /dev/null
@@ -1,83 +0,0 @@
-import Testing
-@testable import SJavaScriptCore
-
-@Test func isUndefined() async throws {
-    let context = JSContext()
-
-    let result = try context.evaluate("undefined")
-    #expect(result.isUndefined)
-    #expect(!result.isNull)
-    #expect(!result.isBool)
-    #expect(!result.isNumber)
-    #expect(!result.isString)
-    #expect(try result.toString() == "undefined")
-}
-
-@Test func isNull() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("null")
-    #expect(!result.isUndefined)
-    #expect(result.isNull)
-    #expect(!result.isBool)
-    #expect(!result.isNumber)
-    #expect(!result.isString)
-    #expect(try result.toString() == "null")
-}
-
-@Test func isBool() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("true")
-    #expect(!result.isUndefined)
-    #expect(!result.isNull)
-    #expect(result.isBool)
-    #expect(!result.isNumber)
-    #expect(!result.isString)
-    #expect(try result.toString() == "true")
-    #expect(result.toBool() == true)
-}
-
-@Test func isNumber() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("3.14")
-    #expect(!result.isUndefined)
-    #expect(!result.isNull)
-    #expect(!result.isBool)
-    #expect(result.isNumber)
-    #expect(!result.isString)
-    #expect(try result.toString() == "3.14")
-    #expect(try result.toDouble() == 3.14)
-}
-
-@Test func isString() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("'success'")
-    #expect(!result.isUndefined)
-    #expect(!result.isNull)
-    #expect(!result.isBool)
-    #expect(!result.isNumber)
-    #expect(result.isString)
-    #expect(try result.toString() == "success")
-}
-
-@Test func toInt() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("40 + 2")
-    #expect(try result.toInt() == 42)
-}
-
-@Test func toString() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("40 + 2")
-    #expect(try result.toString() == "42")
-}
-
-@Test func property() async throws {
-    let context = JSContext()
-    let result = try context.evaluate("""
-        (function(){
-            return { property: 'test' }
-        })()
-        """)
-
-    #expect(try result["property"]?.toString() == "test")
-}
diff --git a/Tests/SJavaScriptCore/JSValue/main.swift b/Tests/SJavaScriptCore/JSValue/main.swift
new file mode 100644
index 0000000..ccdc31e
--- /dev/null
+++ b/Tests/SJavaScriptCore/JSValue/main.swift
@@ -0,0 +1,85 @@
+import Test
+@testable import SJavaScriptCore
+
+test.case("isUndefined") {
+    let context = JSContext()
+
+    let result = try context.evaluate("undefined")
+    expect(result.isUndefined)
+    expect(!result.isNull)
+    expect(!result.isBool)
+    expect(!result.isNumber)
+    expect(!result.isString)
+    expect(try result.toString() == "undefined")
+}
+
+test.case("isNull") {
+    let context = JSContext()
+    let result = try context.evaluate("null")
+    expect(!result.isUndefined)
+    expect(result.isNull)
+    expect(!result.isBool)
+    expect(!result.isNumber)
+    expect(!result.isString)
+    expect(try result.toString() == "null")
+}
+
+test.case("isBool") {
+    let context = JSContext()
+    let result = try context.evaluate("true")
+    expect(!result.isUndefined)
+    expect(!result.isNull)
+    expect(result.isBool)
+    expect(!result.isNumber)
+    expect(!result.isString)
+    expect(try result.toString() == "true")
+    expect(result.toBool() == true)
+}
+
+test.case("isNumber") {
+    let context = JSContext()
+    let result = try context.evaluate("3.14")
+    expect(!result.isUndefined)
+    expect(!result.isNull)
+    expect(!result.isBool)
+    expect(result.isNumber)
+    expect(!result.isString)
+    expect(try result.toString() == "3.14")
+    expect(try result.toDouble() == 3.14)
+}
+
+test.case("isString") {
+    let context = JSContext()
+    let result = try context.evaluate("'success'")
+    expect(!result.isUndefined)
+    expect(!result.isNull)
+    expect(!result.isBool)
+    expect(!result.isNumber)
+    expect(result.isString)
+    expect(try result.toString() == "success")
+}
+
+test.case("toInt()") {
+    let context = JSContext()
+    let result = try context.evaluate("40 + 2")
+    expect(try result.toInt() == 42)
+}
+
+test.case("toString()") {
+    let context = JSContext()
+    let result = try context.evaluate("40 + 2")
+    expect(try result.toString() == "42")
+}
+
+test.case("property") {
+    let context = JSContext()
+    let result = try context.evaluate("""
+        (function(){
+            return { property: 'test' }
+        })()
+        """)
+
+    expect(try result["property"]?.toString() == "test")
+}
+
+test.run()
diff --git a/Tests/SJavaScriptCore/JavaScript.swift b/Tests/SJavaScriptCore/JavaScript/main.swift
similarity index 58%
rename from Tests/SJavaScriptCore/JavaScript.swift
rename to Tests/SJavaScriptCore/JavaScript/main.swift
index 1300bf7..efdc8a5 100644
--- a/Tests/SJavaScriptCore/JavaScript.swift
+++ b/Tests/SJavaScriptCore/JavaScript/main.swift
@@ -1,112 +1,112 @@
-import Testing
+import Test
 @testable import SJavaScriptCore
 
-@Test func evaluate() async throws {
+test.case("evaluate") {
     let context = JSContext()
     _ = try context.evaluate("40 + 2")
 }
 
-@Test func exception() async throws {
+test.case("exception") {
     let context = JSContext()
-    #expect(throws: JSError("Can't find variable: x")) {
+    expect(throws: JSError("Can't find variable: x")) {
         try context.evaluate("x()")
     }
 
-    #expect(throws: JSError("Unexpected end of script")) {
+    expect(throws: JSError("Unexpected end of script")) {
         try context.evaluate("{")
     }
 }
 
-@Test func function() async throws {
+test.case("function") {
     let context = JSContext()
     try context.createFunction(name: "test") { (_) -> Value in
         return .string("success")
     }
     let result = try context.evaluate("test()")
-    #expect(try result.toString() == "success")
+    expect(try result.toString() == "success")
 }
 
-@Test func closure() async throws {
+test.case("closure") {
     let context = JSContext()
 
     try context.createFunction(name: "testUndefined") {
         return .undefined
     }
     let undefinedResult = try context.evaluate("testUndefined()")
-    #expect(undefinedResult.isUndefined)
+    expect(undefinedResult.isUndefined)
 
     try context.createFunction(name: "testNull") {
         return .null
     }
     let nullResult = try context.evaluate("testNull()")
-    #expect(nullResult.isNull)
+    expect(nullResult.isNull)
 
     try context.createFunction(name: "testBool") {
         return .bool(true)
     }
     let boolResult = try context.evaluate("testBool()")
-    #expect(boolResult.isBool)
+    expect(boolResult.isBool)
 
     try context.createFunction(name: "testNumber") {
         return .number(3.14)
     }
     let numberResult = try context.evaluate("testNumber()")
-    #expect(numberResult.isNumber)
+    expect(numberResult.isNumber)
 
     try context.createFunction(name: "testString") {
         return .string("success")
     }
     let stringResult = try context.evaluate("testString()")
-    #expect(stringResult.isString)
+    expect(stringResult.isString)
 }
 
-@Test func capture() async throws {
+test.case("capture") {
     let context = JSContext()
-    final class Box: @unchecked Sendable {
-        var captured = false
-    }
-    let box = Box()
+
+    var captured = false
     try context.createFunction(name: "test") { (_) -> Value in
-        box.captured = true
+        captured = true
         return .string("captured")
     }
     let result = try context.evaluate("test()")
-    #expect(box.captured == true)
-    #expect("\(result)" == "captured")
+    expect(captured)
+    expect("\(result)" == "captured")
 }
 
-@Test func arguments() async throws {
+test.case("arguments") {
     let context = JSContext()
     try context.createFunction(name: "test") { (arguments) -> Void in
-        #expect(arguments.count == 2)
-        try #expect(arguments.first?.toString() == "one")
-        try #expect(arguments.last?.toInt() == 42)
+        expect(arguments.count == 2)
+        expect(try arguments.first?.toString() == "one")
+        expect(try arguments.last?.toInt() == 42)
     }
     try context.evaluate("test('one', 42)")
 }
 
-@Test func `persistent context`() async throws {
+test.case("persistent context") {
     let context = JSContext()
     try context.evaluate("result = 'success'")
-    #expect(try context.evaluate("result").toString() == "success")
+    expect(try context.evaluate("result").toString() == "success")
 
-    try context.createFunction(name: "test") { (_) -> Value in
+    try context.createFunction(name: "test") { (arguments) -> Value in
         return .string("test ok")
     }
 
-    #expect(try context.evaluate("result").toString() == "success")
+    expect(try context.evaluate("result").toString() == "success")
 }
 
-@Test func sandbox() async throws {
+test.case("sandbox") {
     try {
         let context = JSContext()
         try context.evaluate("test = 'hello'")
         let result = try context.evaluate("test")
-        #expect(try result.toString() == "hello")
+        expect(try result.toString() == "hello")
     }()
 
     let context = JSContext()
-    #expect(throws: JSError("Can\'t find variable: test")) {
+    expect(throws: JSError("Can\'t find variable: test")) {
         try context.evaluate("test")
     }
 }
+
+test.run()
diff --git a/run_tests b/run_tests
new file mode 100755
index 0000000..ff5b535
--- /dev/null
+++ b/run_tests
@@ -0,0 +1,10 @@
+#!/bin/bash
+
+set -e
+
+swift build
+
+export DYLD_LIBRARY_PATH=/Library/Developer/Toolchains/swift-latest.xctoolchain/usr/lib/swift/macosx
+
+.build/debug/Tests/SJavaScriptCore/JavaScript
+.build/debug/Tests/SJavaScriptCore/JSValue