Swift Mock filesystem?

InfRandomness · June 29, 2022, 12:39am

Hey everyone,

I'm currently writing some tests for my code (which reads from files and directories)
I was told to use a Mock filesystem instead of manually creating a bunch of directories / files into my test's setUp methods
Does anyone know if that's a good idea ? Is there any good library out there that'd "mock" the FileManager / URL library and let me create in-memory file?

vermont42 · June 29, 2022, 2:53am

No need for a library. Just use a protocol instead of actual filesystem APIs and create a mock implementation for unit tests and a real implementation for production. I did something similar for UserDefaults access.

github.com

vermont42/Conjugar/blob/master/Conjugar/GetterSetter.swift

//
//  GetterSetter.swift
//  Conjugar
//
//  Created by Joshua Adams on 1/13/19.
//  Copyright © 2019 Josh Adams. All rights reserved.
//

import Foundation

protocol GetterSetter {
  func get(key: String) -> String?
  func set(key: String, value: String)
}

github.com

vermont42/Conjugar/blob/master/Conjugar/DictionaryGetterSetter.swift

//
//  DictionaryGetterSetter.swift
//  Conjugar
//
//  Created by Joshua Adams on 1/13/19.
//  Copyright © 2019 Josh Adams. All rights reserved.
//

import Foundation

class DictionaryGetterSetter: GetterSetter {
  var dictionary: [String: String] = [:]

  init() {}

  init(dictionary: [String: String]) {
    self.dictionary = dictionary
  }

  func get(key: String) -> String? {

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github.com

vermont42/Conjugar/blob/master/Conjugar/UserDefaultsGetterSetter.swift

//
//  UserDefaultsGetterSetter.swift
//  Conjugar
//
//  Created by Joshua Adams on 1/13/19.
//  Copyright © 2019 Josh Adams. All rights reserved.
//

import Foundation

class UserDefaultsGetterSetter: GetterSetter {
  private let userDefaults = UserDefaults.standard

  func get(key: String) -> String? {
    return userDefaults.string(forKey: key)
  }

  func set(key: String, value: String) {
    userDefaults.set(value, forKey: key)
  }

This file has been truncated. show original

Jon_Shier · June 29, 2022, 3:20am

It’s also fine to test writing real files. Purity for purity’s sake helps no one.

InfRandomness · June 30, 2022, 4:41am

I have decided to opt for Bundles to feed pre existing files and directories for my tests to work against but I can't quite get a path to the bundles I have created

with my package.swift file being :

// swift-tools-version: 5.6
// The swift-tools-version declares the minimum version of Swift required to build this package.

import PackageDescription

let package = Package(
  name: "Swatter",
  dependencies: [
    // Dependencies declare other packages that this package depends on.
    // .package(url: /* package url */, from: "1.0.0"),
    .package(url: "https://github.com/apple/swift-syntax.git", from: "0.50600.1"),
    .package(url: "https://github.com/apple/swift-argument-parser", from: "1.0.0"),
  ],
  targets: [
    // Targets are the basic building blocks of a package. A target can define a module or a test suite.
    // Targets can depend on other targets in this package, and on products in packages this package depends on.
    .executableTarget(
      name: "Swatter",
      dependencies: [
        .product(name: "SwiftSyntax", package: "swift-syntax"),
        .product(name: "ArgumentParser", package: "swift-argument-parser"),
      ]),
    .testTarget(
      name: "SwatterTests",
      dependencies: [
        "Swatter"
      ],
      resources: [.copy("ProjectTests")]),
  ]
)

my project structure being :

Calling this code

    let test = Bundle(for: type(of: self))
    print(test.bundlePath)

inside the test returns a result to the debug directory of my build "/home/infrandomness/Documents/Dev/Swatter/.build/x86_64-unknown-linux-gnu/debug"

and after a bit of searching around, the files are copied, but the returned bundlePath is not correct :

[infrandomness@fedora Swatter]$ find . -name Cartfile
./Tests/SwatterTests/ProjectTests/TestIsValidProject/Carthage/Cartfile <- original file
./.build/x86_64-unknown-linux-gnu/debug/Swatter_SwatterTests.resources/ProjectTests/TestIsValidProject/Carthage/Cartfile <- correct file path

phoneyDev · June 30, 2022, 5:12pm

One reason to use mocks is that they'll be faster than the actual APIs. This is likely true for Networking APIs but file system APIs are pretty fast anyway. I use the file system APIs directly in my tests with no problems.
If whoever told you to use file system mocks didn't tell you what mock library they use, well...