Implemented the FileServiceSpy spy in the Tests target.

Tests/Library/Helpers/Spies/FileServiceSpy.swift

@@ -0,0 +1,47 @@
+import Foundation
+
+@testable import ColibriLibrary
+
+final class FileServiceSpy {
+    
+    // MARK: Properties
+    
+    private(set) var isCreateFolderCalled: Bool = false
+    private(set) var isDeleteCalled: Bool = false
+    private(set) var isExistsAtCalled: Bool = false
+    private(set) var urlCalled: URL?
+    
+}
+
+// MARK: - FileServicing
+
+extension FileServiceSpy: FileServicing {
+    var currentFolder: URL {
+        get async { .someCurrentFolder }
+    }
+    
+    func createFolder(at url: URL) async throws(FileServiceError) {
+        isCreateFolderCalled = true
+        urlCalled = url
+    }
+    
+    func delete(at url: URL) async throws(FileServiceError) {
+        isDeleteCalled = true
+        urlCalled = url
+    }
+    
+    @discardableResult
+    func exists(at url: URL) async throws(FileServiceError) -> Bool {
+        isExistsAtCalled = true
+        urlCalled = url
+        
+        return .random()
+    }
+    
+}
+
+// MARK: - URL+Constants
+
+private extension URL {
+    static let someCurrentFolder = URL(at: "some/current/folder")
+}