         var fs = InMemoryFileSystem()
         try fs.createEmptyFiles("/Sources/main.swift",
                                 "/Sources/main.c")
-        PackageBuilderTester(.root, in: fs) { result in
+        PackageBuilderTester("MixedSources", in: fs) { result in
             result.checkError("the module at /Sources contains mixed language source files fix: use only a single language within a module")
         }
     }

    var ignoreOtherModules: Bool = false

    @discardableResult
    init(_ path: AbsolutePath, in fs: FileSystem, package: PackageDescription.Package? = nil, file: StaticString = #file, line: UInt = #line, _ body: @noescape (PackageBuilderTester) -> Void) {
        do {
            let loadedPackage = try loadPackage(path, in: fs, package: package)
            result = .package(loadedPackage)
            uncheckedModules = Set(loadedPackage.allModules)
        } catch {

    }
}

/// Loads a package using PackageBuilder at the given path.
///
/// - Parameters:
///     - package: PackageDescription instance to use for loading this package.
///     - path: Directory where the package is located.
///     - in: FileSystem in which the package should be loaded from.
///
/// - Throws: ModuleError, ProductError
private func loadPackage(_ package: PackageDescription.Package, path: AbsolutePath, in fs: FileSystem) throws -> PackageModel.Package {
    let manifest = Manifest(path: path.appending(component: Manifest.filename), url: "", package: package, products: [], version: nil)
    let builder = PackageBuilder(manifest: manifest, path: path, fileSystem: fs)
    return try builder.construct(includingTestModules: true)
}
