Mockit - A Tasty mocking framework for unit tests in Swift 5.0

by iOS Example

Mockit

Introduction

Mockit is a Tasty mocking framework for unit tests in Swift 5.0. It's at an early stage of development, but its current features are almost completely usable.

Mockit is a mocking framework that tastes brilliant. It lets you write beautiful tests with a clean & simple API. Tests written using Mockit are very readable and they produce clean verification errors. It's inspired by the famous mocking framework for Java - Mockito.

Documentation

Mockit is yet to be documented fully but it comes with a sample project that lets you try all its features and become familiar with the API. You can find it in Mockit.xcworkspace.

There's an example test file called ExampleTests.swift. Look there for some tests that can be run. This tests a class Example against a mocked collaborator ExampleCollaborator.

File an issue if you have any question.

To run the example project, clone the repo, and run pod install from the Example directory first.

Limitations

  • There's some boiler-plate code needed to create mocks. See MockExampleCollaborator for an example in the Basic Usage section below. However, a plugin development is on its way for both Xcode and AppCode to minimize writing this boiler-plate code every time a mock needs to be created.

Features

  • Stubbing. Mockit lets you stub a method and then perform any of 3 actions (thenReturn, thenDo, thenAnswer) individually or in any order via chaining;

  • Mocking. You can create a subclass extending the Mock protocol to mock required methods;

  • Call Verification. You can verify method calls using one of 8 supported modes (Once, AtLeastOnce, AtMostOnce, Times, AtLeastTimes, AtMostTimes, Never and Only);

  • Arguments of specific call. Mockit allows you to obtain the arguments of a specific method call to use custom assertions on them;

  • Helpful messages. If method verification fails or something goes wrong, Mockit provides readable messages that describes the issue;

  • Default Type matchers. Out of the box, Mockit can match the following types:

    • String / String?
    • Bool / Bool?
    • Int / Int?
    • Double / Double?
    • Float / Float?
    • Array / Array? of the above primitive types
    • Dictionary / Dictionary? of the above primitive types

Given that Swift does not have reflection, Mockit cannot magically match your custom types, so you need to subclass TypeMatcher protocol to write
your one custom type matcher. For an example, see the Basic Usage section below.

Basic Usage

The examples below assume we are mocking this class:

class ExampleCollaborator {

    func voidFunction() {
    }

    func function(int: Int, _ string: String) -> String {
      return ""
    }

    func stringDictFunction(dict: [String: String]) -> String {
      return ""
    }

}

In your test code, you'll need to create a MockExampleCollaborator, which extends ExampleCollaborator and adopts Mock. The mock creates a CallHandler, and forwards all calls to it:

class MockExampleCollaborator: ExampleCollaborator, Mock {

    let callHandler: CallHandler

    init(testCase: XCTestCase) {
      callHandler = CallHandlerImpl(withTestCase: testCase)
    }

    func instanceType() -> MockExampleCollaborator {
      return self
    }

    override func voidFunction() {
      callHandler.accept(nil, ofFunction: #function, atFile: #file, inLine: #line, withArgs: nil)
    }

    override func function(int: Int, _ string: String) -> String {
      return callHandler.accept("", ofFunction: #function, atFile: #file, inLine: #line, withArgs: int, string) as! String
    }

    override func stringDictFunction(dict: Dictionary<String, String>) -> String {
      return callHandler.accept("", ofFunction: #function, atFile: #file, inLine: #line, withArgs: dict) as! String
    }

}

To write a custom type matcher:

public class CustomMatcher: TypeMatcher {

    public func match(argument arg: Any, withArgument withArg: Any) -> Bool {
      switch (arg, withArg) {
        case ( _ as CustomType, _ as CustomType):
          // custom matching code here
          return true
        default:
          return false
      }
    }

}

It is good practice to put the mock objects and custom type matchers in a separate group in the test part of your project.

Currently-supported syntax

// stub a call on a method with parameters, then return value
mockCollaborator.when().call(withReturnValue: mockCollaborator.function(42, "frood")).thenReturn("hoopy")

// stub a call on a method with dictionary parameter, then answer value
mockCollaborator.when().call(withReturnValue: mockCollaborator.stringDictFunction(["Hello": "Pong"])).thenAnswer {
      (args: [Any?]) -> String in

      // custom code here
    }

// stub a call on a void method , then do action
mockCollaborator.when().call(withReturnValue: mockCollaborator.voidFunction()).thenDo {
      (args: [Any?]) -> Void in

      // if the call is received, this closure will be executed
      print("===== thenDo closure called =====")
    }

// stub a call on a method , then return values on multiple calls
mockCollaborator.when().call(withReturnValue: mockCollaborator.stringDictFunction(["Hello": "Pong"])).thenReturn("ping", "hoopy")

// stub a call on a method , then chain multiple actions for corresponding calls
mockCollaborator.when().call(withReturnValue: mockCollaborator.stringDictFunction(["Hello": "Pong"])).thenReturn("ping", "hoopy").thenAnswer {
      (args: [Any?]) -> String in

      // custom code here
    }

// call a method and then get arguments of a specific call which can be asserted later
systemUnderTest.doSomethingWithParamters(42, "frood")
systemUnderTest.doSomethingWithParamters(18, "hoopy")

let argumentsOfFirstCall = mockCollaborator.getArgs(callOrder: 1).of(mockCollaborator.function(AnyValue.int, AnyValue.string))
let argumentsOfSecondCall = mockCollaborator.getArgs(callOrder: 2).of(mockCollaborator.function(AnyValue.int, AnyValue.string))

With nice mocks, Mockit supports the "verify expectations after mocking" style using 8 supported verification modes

// call method on the system under test
systemUnderTest.expectMethodOneAndThree()

// Then
mockCollaborator.verify(verificationMode: Once()).methodOne()
mockCollaborator.verify(verificationMode: Never()).methodTwo()
mockCollaborator.verify(verificationMode: Once()).methodThree()


// call method on the system under test
sut.expectMethodOneTwice()

// Then
mockCollaborator.verify(verificationMode: Times(times: 2)).methodOne()


// call method on the system under test
sut.expectOnlyMethodThree()

// Then
mockCollaborator.verify(verificationMode: Only()).methodThree()


// call method on system under test
sut.expectAllThreeMethods()

// Then
mockCollaborator.verify(verificationMode: Once()).methodOne()
mockCollaborator.verify(verificationMode: AtLeastOnce()).methodTwo()
mockCollaborator.verify(verificationMode: AtMostOnce()).methodThree()


// call method on the system under test
sut.expectMethodTwoAndThree()

// Then
mockCollaborator.verify(verificationMode: AtLeastTimes(times: Times(times: 1))).methodTwo()
mockCollaborator.verify(verificationMode: Never()).methodOne()
mockCollaborator.verify(verificationMode: AtMostTimes(times: Times(times: 3))).methodThree()

Requirements

  • Xcode 9+
  • XCTest

Installation

Mockit is built with Swift 5.0.

CocoaPods

Mockit is available through CocoaPods. To install
it, simply add the following line to your Podfile:

pod 'Mockit', '1.5.0'

Manually

  1. Download and drop /Mockit folder in your project.
  2. Congratulations!

Feedback

Issues and pull-requests are most welcome - especially about improving the API further.

Author

Syed Sabir Salman-Al-Musawi, sabirvirtuoso@gmail.com

I'd also like to thank Sharafat Ibn Mollah Mosharraf for his big support during the API design and development phase.

License

Mockit is available under the MIT license. See the LICENSE file for more info.

The PNG at the top of this README.md is from www.mockit.co.uk/about.html

GitHub

https://github.com/sabirvirtuoso/Mockit