Root folder creation (#2)

This PR contains the work done to create the root folder of a new project when executing the _colibri_ executable. In addition, some other work has been done:

* added the `ArgumentParser` package dependency to the package;
* implemented the `FileService` service in the _library_ target;
* implemented the `CreateRootFolderTask` task in the _library_ target;
* removed some unnecessary comments and boilerplate code;

Reviewed-on: #2
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Tests/Library/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: "~")
+    
+}

Tests/Library/Helpers/Mocks/FileServiceMock.swift

@@ -0,0 +1,84 @@
+import ColibriLibrary
+import Foundation
+
+struct FileServiceMock {
+    
+    // MARK: Properties
+    
+    private let action: Action?
+    private let folder: URL
+    
+    private weak var spy: FileServiceSpy?
+    
+    // MARK: Initialisers
+    
+    init(
+        currentFolder: URL,
+        action: Action? = nil,
+        spy: FileServiceSpy? = nil
+    ) {
+        self.action = action
+        self.folder = currentFolder
+        self.spy = spy
+    }
+    
+}
+
+// MARK: - FileServicing
+
+extension FileServiceMock: FileServicing {
+    
+    // MARK: Computed
+    
+    var currentFolder: URL {
+        get async { folder }
+    }
+    
+    // MARK: Functions
+    
+    func createFolder(at url: URL) async throws(FileServiceError) {
+        switch action {
+        case .error(let error):
+            throw error
+        case let .createFolder(url):
+            try await spy?.createFolder(at: url)
+        default:
+            break
+        }
+    }
+    
+    func delete(at url: URL) async throws(FileServiceError) {
+        switch action {
+        case .error(let error):
+            throw error
+        case let .delete(url):
+            try await spy?.delete(at: url)
+        default:
+            break
+        }
+    }
+    
+    func exists(at url: URL) async throws(FileServiceError) -> Bool {
+        switch action {
+        case .error(let error):
+            throw error
+        case let .exists(url, exists):
+            try await spy?.exists(at: url)
+            return exists
+        default:
+            return false
+        }
+    }
+    
+}
+
+// MARK: - Enumerations
+
+extension FileServiceMock {
+    enum Action {
+        case createFolder(URL)
+        case delete(URL)
+        case error(FileServiceError)
+        case exists(URL, Bool)
+    }
+}

Tests/Library/Helpers/Spies/FileServiceSpy.swift

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+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()
+    }
+    
+}