Restructured the folder structure of the test target.

Test/Sources/Helpers/Extensions/URL+Samples.swift

@@ -0,0 +1,18 @@
+import Foundation
+
+@testable import ColibriLibrary
+
+extension URL {
+    
+    // MARK: Constants
+    
+    static let someCurrentFolder = URL(at: "/some/current/folder")
+    static let someDotFolder = URL(at: ".")
+    static let someExistingFolder = URL(at: "/some/existing/folder")
+    static let someExistingFile = URL(at: "/some/existing/file")
+    static let someNewFolder = URL(at: "/some/new/folder")
+    static let someNewFile = URL(at: "/some/new/file")
+    static let someRandomURL = URL(string: "http://some.random.url")!
+    static let someTildeFolder = URL(at: "~")
+    
+}

Test/Sources/Helpers/Mocks/FileServiceMock.swift

@@ -0,0 +1,135 @@
+import ColibriLibrary
+import Foundation
+
+final class FileServiceMock {
+    
+    // MARK: Properties
+    
+    private let folder: URL
+    
+    private var actions: [Action] = []
+    
+    private weak var spy: FileServiceSpy?
+    
+    // MARK: Initialisers
+    
+    init(
+        currentFolder: URL,
+        action: Action? = nil,
+        spy: FileServiceSpy? = nil
+    ) {
+        self.actions = if let action {
+            [action]
+        } else {
+            []
+        }
+        self.folder = currentFolder
+        self.spy = spy
+    }
+    
+    init(
+        currentFolder: URL,
+        actions: [Action],
+        spy: FileServiceSpy? = nil
+    ) {
+        self.actions = actions
+        self.folder = currentFolder
+        self.spy = spy
+    }
+    
+}
+
+// MARK: - FileServicing
+
+extension FileServiceMock: FileServicing {
+
+    // MARK: Computed
+    
+    var currentFolder: URL {
+        get async { folder }
+    }
+    
+    // MARK: Functions
+    
+    func copyItem(from source: URL, to destination: URL) async throws (FileServiceError) {
+        guard let nextAction else { return }
+        
+        switch nextAction {
+        case .error(let error):
+            throw error
+        case let .copyItem(source, destination):
+            try await spy?.copyItem(from: source, to: destination)
+        default:
+            break
+        }
+    }
+    
+    func createFolder(at location: URL) async throws (FileServiceError) {
+        guard let nextAction else { return }
+        
+        switch nextAction {
+        case .error(let error):
+            throw error
+        case let .createFolder(location):
+            try await spy?.createFolder(at: location)
+        default:
+            break
+        }
+    }
+    
+    func deleteItem(at location: URL) async throws (FileServiceError) {
+        guard let nextAction else { return }
+        
+        switch nextAction {
+        case .error(let error):
+            throw error
+        case let .deleteItem(location):
+            try await spy?.deleteItem(at: location)
+        default:
+            break
+        }
+    }
+    
+    func isItemExists(at location: URL) async throws (FileServiceError) -> Bool {
+        guard let nextAction else { return false }
+        
+        switch nextAction {
+        case .error(let error):
+            throw error
+        case let .isItemExists(location, exists):
+            try await spy?.isItemExists(at: location)
+            return exists
+        default:
+            return false
+        }
+    }
+    
+}
+
+// MARK: - Helpers
+
+private extension FileServiceMock {
+    
+    // MARK: Computed
+    
+    var nextAction: Action? {
+        guard !actions.isEmpty else {
+            return nil
+        }
+
+        return actions.removeFirst()
+    }
+    
+}
+
+// MARK: - Actions
+
+extension FileServiceMock {
+    enum Action {
+        case copyItem(URL, URL)
+        case createFolder(URL)
+        case deleteItem(URL)
+        case error(FileServiceError)
+        case isItemExists(URL, Bool)
+    }
+}

Test/Sources/Helpers/Spies/FileServiceSpy.swift

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+import Foundation
+
+@testable import ColibriLibrary
+
+final class FileServiceSpy {
+    
+    // MARK: Properties
+    
+    private(set) var actions: [Action] = []
+    
+}
+
+// MARK: - FileServicing
+
+extension FileServiceSpy: FileServicing {
+
+    var currentFolder: URL {
+        get async { .someCurrentFolder }
+    }
+    
+    func copyItem(from source: URL, to destination: URL) async throws (FileServiceError) {
+        actions.append(.itemCopied(source, destination))
+    }
+    
+    func createFolder(at location: URL) async throws (FileServiceError) {
+        actions.append(.folderCreated(location))
+    }
+    
+    func deleteItem(at location: URL) async throws (FileServiceError) {
+        actions.append(.itemDeleted(location))
+    }
+    
+    @discardableResult
+    func isItemExists(at location: URL) async throws (FileServiceError) -> Bool {
+        actions.append(.itemExists(location))
+
+        return .random()
+    }
+    
+}
+
+// MARK: - Action
+
+extension FileServiceSpy {
+    enum Action: Equatable {
+        case folderCreated(_ location: URL)
+        case itemCopied(_ source: URL, _ destination: URL)
+        case itemDeleted(_ location: URL)
+        case itemExists(_ location: URL)
+    }
+}