A Mocking Framework for Swift Unit Tests
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README.md

For detailed instructions, see my blog entry!

Installation

Add pod 'MockFive' to your Podfile, or include both swift files from the MockFive directory to your project.

One Mock, Many Tests

MockFive allows you to make a single mock for a class or protocol. You can then configure instances of this mock with stubbed implementations. For any commonly used class, MockFive can offer a powerful means to satisfy Swift's strict typing system without sacrificing power. Because of Swift's strict typing, you must implement every method you intend to mock with calls to MockFive's stub().

// Optional types will return `nil` by default
func myFunc(arg1: Int, arg2: String) -> String? {
    return stub(identifier: "myFunc", arguments: arg1, arg2)
}

// Non-optional types require a default value
var customItem = MyCustomClass() // This may be changed later. stub will return new value
func myFunc() -> MyCustomClass {
    return stub(identifier: "myFunc") { customItem }
}

In order to work properly, a mocked function must do three things. It must return the result of a call to stub(), it must provide a unique string for the identifier parameter, and it must pass its arguments through the arguments parameter. If the return type of the function is Void or is an optional type, stub() will return Void or nil as appropriate by default. In other cases, such as Int, a closure must be provided with a default value. In the case of class stubs, it is often useful to call super by default. This creates a mock that behaves exactly like a production object, but tracks all method calls and allows stubbing.

Protocol Mocking

import MockFive

//MARK: Production file -------------------------------------------------------------------------------------
struct CustomModel { var id: Int }

protocol MockworthyProtocol {
    func method()
    func complexMethod(arg: Int, model: CustomModel, others: Any?...) -> (Int, String)
}

//MARK: Testing utilities file ------------------------------------------------------------------------------
struct MockImplementation: MockworthyProtocol, Mock {
    let mockFiveLock = lock()
    
    func method() { stub(identifier: "method") }
    func complexMethod(arg: Int, model: CustomModel, others: Any?...) -> (Int, String) { _ -> (Int, String) in
        return stub(identifier: "complexMethod", arguments: arg, model.id, others) { (37, "stub string") }
    }
}

//MARK: Test file --------------------------------------------------------------------------------------------
var mock = MockImplementation()

// Invocation records
mock.method()
mock.complexMethod(7, model: CustomModel(id: 982), others: 7, nil, 0.23, [0,9]) // (37, "stub string")

mock.invocations[0] // "method()"
mock.invocations[1] // "complexMethod(_: 7, model: 982, others: [Optional(7), nil, Optional(0.23), Optional([0, 9])]) -> (Int, String)"

// Function stubbing
mock.registerStub("complexMethod") { (90, "Total \(42 + 9)") }
mock.complexMethod(9, model: CustomModel(id: 7)) // (90, "Total 51")

Class Mocking

import MockFive

//MARK: Production file -------------------------------------------------------------------------------------
struct CustomModel { var id: Int }

class MockworthyClass {
    func method() {}
    func complexMethod(arg: Int, model: CustomModel, others: Any?...) -> (Int, String) { return (9, "potatos") }
}

//MARK: Testing utilities file ------------------------------------------------------------------------------
class MockwortheClassMock: MockworthyClass, Mock {
    let mockFiveLock = lock()
    
    override func method() { stub(identifier: "method") { super.method() } }
    override func complexMethod(arg: Int, model: CustomModel, others: Any?...) -> (Int, String) { _ -> (Int, String) in
        return stub(identifier: "complexMethod", arguments: arg, model.id, others) { 
            super.complexMethod(arg, model: model, others: others) 
        }
    }
}

//MARK: Test file --------------------------------------------------------------------------------------------
var mock = MockwortheClassMock()

// Invocation records
mock.method()
mock.complexMethod(7, model: CustomModel(id: 982), others: 7, nil, 0.23, [0,9]) // (37, "stub string")

mock.invocations[0] // "method()"
mock.invocations[1] // "complexMethod(_: 7, model: 982, others: [Optional(7), nil, Optional(0.23), Optional([0, 9])]) -> (Int, String)"

// Function stubbing
mock.registerStub("complexMethod") { (90, "Total \(42 + 9)") }
mock.complexMethod(9, model: CustomModel(id: 9)) // (90, "Total 51")

See more examples in TestTrack.playground in the project!