MockItYourself

MockItYourself is an attempt to create a mocking framework for Swift. Currently, you can't dynamically create classes in Swift and it is therefore impossible to create a powerful mocking framework like OCMock. MockItYourself is an attempt to reduce the boilerplate needed to manually create mocks.

MockItYourself is heavily inspired by SwiftMock and could in some ways be considered a fork of that project.

Installation

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

source 'https://github.com/CocoaPods/Specs.git'

use_frameworks!

target 'MyApp' do

end

target 'MyApp_Tests', :exclusive => true do
    pod 'MockItYourself', '1.0.0'
end

Motivation

The standard way of mocking out dependencies in Swift is to manually create your own mocks:

class Dependency {
    func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        print("Do something really slow and expensive with arguments")
        return 40.0
    }
}

class MockDependency: Dependency {
    var didCallSlowAndExpensiveMethod: Bool = false
    var lastCalledArg1: String?
    var lastCalledArg2: Int?
    
    override func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        didCallSlowAndExpensiveMethod = true
        lastCalledArg1 = arg1
        lastCalledArg2 = arg2
        
        return 50.0
    }
}

struct ObjectUnderTests {
    let dependency: Dependency
    
    func method() -> Double {
        let result = dependency.slowAndExpensiveMethod("A", arg2: 1)
        return result / 2
    }
}

class MockExampleTests: XCTestCase {
    var mockDependency: MockDependency!
    var objectUnderTest: ObjectUnderTests!
    
    override func setUp() {
        mockDependency = MockDependency()
        objectUnderTest = ObjectUnderTests(dependency: mockDependency)
    }
    
    func test_did_call_method_on_dependency_with_correct_arguments() {
        let _ = objectUnderTest.method()
        
        XCTAssert(mockDependency.didCallSlowAndExpensiveMethod)
        XCTAssertEqual(mockDependency.lastCalledArg1, "A")
        XCTAssertEqual(mockDependency.lastCalledArg2, 1)
    }
    
    func test_method_returns_correct_result_given_dependency_returns_50() {
        let result = objectUnderTest.method()
        
        XCTAssertEqual(result, 25.0)
    }
}

This quickly becomes tedious and MockItYourself is an attempt to reduce the boilerplate.

class Dependency {
    func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        print("Do something really slow and expensive with arguments")
        return 40.0
    }
}

class MockDependency: Dependency, MockItYourself {
    let callHandler = MockCallHandler()
    
    override func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        return callHandler.registerCall(args: Args2(arg(arg1), arg(arg2)), defaultReturnValue: 50) as! Double
    }
}

struct ObjectUnderTests {
    let dependency: Dependency
    
    func method() -> Double {
        let result = dependency.slowAndExpensiveMethod("A", arg2: 1)
        return result / 2
    }
}

class MockExampleTests: XCTestCase {
    var mockDependency: MockDependency!
    var objectUnderTest: ObjectUnderTests!
    
    override func setUp() {
        mockDependency = MockDependency()
        objectUnderTest = ObjectUnderTests(dependency: mockDependency)
    }
    
    func test_did_call_method_on_dependency_with_correct_arguments() {
        let _ = objectUnderTest.method()
        
        verify(mockDependency) { self.mockDependency.slowAndExpensiveMethod("A", arg2: 1) }
    }
    
    func test_method_returns_correct_result_given_dependency_returns_50() {
        stub(mockDependency, andReturnValue: 50) { mockDependency.slowAndExpensiveMethod("A", arg2: 1) }

        let result = objectUnderTest.method()
        
        XCTAssertEqual(result, 25.0)
    }
}

Usage

MockItYourself helps reduce boilerplate when manually creating mocks. Let's imagine that we have the following class:

class Dependency {
    func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        return 40.0
    }
}

Creating the mock is simple:

1. Create a subclass of Dependency.
2. Implement the MockItYourself protocol by adding a callHandler property.
3. Register the methods that you want to mock or stub.

import MockItYourself

class MockDependency: Dependency, MockItYourself {
    let callHandler = MockCallHandler()
    
    override func slowAndExpensiveMethod(arg1: String, arg2: Int) -> Double {
        return callHandler.registerCall(args: Args2(arg(arg1), arg(arg2)), defaultReturnValue: 50)
    }
}

Verify

MockItYourself allows you to verify if methods on your mocks are called with the

To verify a method was called:

func test_verify() {
    mock.slowAndExpensiveMethod("A", arg2: 1)
    
    verify(mock) { self.mock.slowAndExpensiveMethod(any(), arg2: any()) }
}

To verify a method was called n number of times:

func test_verify_number_of_calls() {
    mock.slowAndExpensiveMethod("A", arg2: 1)
    mock.slowAndExpensiveMethod("A", arg2: 1)

    verify(mock, expectedCallCount: 2) { self.mock.slowAndExpensiveMethod(any(), arg2: any()) }
}

To verify a method was called with the specific arguments:

func test_verify_with_arguments() {
    mock.slowAndExpensiveMethod("A", arg2: 1)

    verify(mock, checkArguments: true) { self.mock.slowAndExpensiveMethod("A", arg2: 1) }
}

Reject

To verify a method was not called:

func test_reject() {
    reject(mock) { self.mock.slowAndExpensiveMethod("A", arg2: 1) }
}

Stubbing

To stub out the return value of a method or property:

func test_stubbing() {
    stub(mock, andReturnValue: 30) { self.mock.slowAndExpensiveMethod("A", arg2: 1) }

    let returnValue = mock.slowAndExpensiveMethod("A", arg2: 1)
    XCTAssertEqual(returnValue, 30)
}

Authors

• Alexey Verein, alexey@plainvanillagames.com
• Jóhann Þ. Bergþórsson, johann@plainvanillagames.com
• Magnus Ó. Magnússon, magnus@plainvanillagames.com
• Alexander A. Helgason, alliannas@plainvanillagames.com

License

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