An Xcode extension (plugin) to generate Swift test doubles automatically.
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EndToEndTestHost Adds crashlytics Jul 12, 2018
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XcodePlugin Implements partial spy Oct 20, 2018
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Swift Mock Generator Xcode Source Editor Extension

Mock Generator Icon

An Xcode extension (plugin) to generate spy, stub, dummy, and partial spy classes automatically.

Xcode mock generator

Looking for the AppCode version?

Install Swift Mock Generator Xcode Source Editor Extension

  • Close Xcode if it is open
  • Download the latest release here
  • Copy the app to the Applications folder.
  • Open the app
  • For Mojave users, select OK for '"Swift Mock Generator for Xcode" wants access to control "Xcode"'
  • Go to System Preferences -> Extensions -> Xcode Source Editor and make sure Mock Generator is enabled.
  • For Mojave users, go to System Preferences -> Security & Privacy -> Privacy -> Automation and make sure Swift Mock Generator is enabled.
  • Open Xcode

How to create a new Swift test double

  • Create an empty class inheriting from a class or protocols that you wish to mock.


class MyProtocolSpy: MyProtocol {
  • Place the cursor inside the class declaration.
  • Click Editor -> Mock Generator -> Generate spy.

How to recreate a Swift mock

There's no need to delete the old code. Simply place the cursor anywhere inside the class declaration and generate the test double as before.

Recommended: assign a shortcut

  • Select preferences ⌘, in Xcode.
  • Choose 'Key Bindings'.
  • Search for 'Mock Generator'.
  • Choose your preferred shortcut.

Recommended: use a version control system

The mock generator will replace anything that is currently in your class with the generated test double.

Undo is supported for Xcode plugins but you're safer to use a version control system such as git in the event of unexpectedly generating a test double.


Feature Supported
Swift 3 and 4.
Generate a spy.
Generate a stub.
Generate a dummy.
Generate a partial spy.
Classes and protocols
Generates test doubles conforming to one or many protocols.
Generates test doubles conforming to a class. *
Generates test doubles conforming to both classes and protocols. *
Recording methods and properties
Captures invocation status of methods.
Captures invocation status of properties.
Records multiple invocations of methods.
Records multiple invocations of properties.
Captures invoked method parameters.
Records multiple invocations of method parameters.
Supports multiple properties in the same declaration.
Stubbing return values and closures
Stubs values for your test doubles to return.
Stubs a default value for return values where possible.
Automatically calls closure parameters with stubbed values.
Generates convenience initializers requiring no parameters.
Supports initializers with arguments.
Supports failable initializers.
Supports required initializers.
Stub an error for your overridden method to throw.
Supports throwing initializers.
Supports throwing closures.
Generates generic test doubles from protocols with associated types.
Captures invoked generic parameters. **
Captures invoked generic return values. **
Scope, keywords, and more
Avoids naming clashes from overloaded methods.
Supports parameter type-annotation attributes and inout.
Respects the test double scope and generates public and open methods and properties.
Generate test doubles inheriting from items in 3rd party frameworks.

* properties with inferred types are not supported

** generic arguments in closures and generic types are not supported

Feature requests

If there is a feature you need, check for an existing GitHub issue and make a comment or, if no issue exists, raise a new issue.

Usage example

A protocol called Animator that we wish to spy on:

protocol Animator {
  func animate(duration: TimeInterval, animations: () -> (), completion: (Bool) -> ()) -> Bool

Create a spy class conforming to a protocol:

class AnimatorSpy: Animator {

Generate the spy:

class AnimatorSpy: Animator {

  var invokedAnimate = false
  var invokedAnimateCount = 0
  var invokedAnimateParameters: (duration: TimeInterval, Void)?
  var invokedAnimateParametersList = [(duration: TimeInterval, Void)]()
  var shouldInvokeAnimateAnimations = false
  var stubbedAnimateCompletionResult: (Bool, Void)?
  var stubbedAnimateResult: Bool! = false

  func animate(duration: TimeInterval, animations: () -> (), completion: (Bool) -> ()) -> Bool {
    invokedAnimate = true
    invokedAnimateCount += 1
    invokedAnimateParameters = (duration, ())
    invokedAnimateParametersList.append((duration, ()))
    if shouldInvokeAnimateAnimations {
    if let result = stubbedAnimateCompletionResult {
    return stubbedAnimateResult

Inject the spy into the class you wish to test:

let animatorSpy = AnimatorSpy()
let object = ObjectToTest(animator: animatorSpy)

Test if animate method was invoked:

func test_spyCanVerifyInvokedMethod() {

Test the correct parameter was passed to the animate method:

func test_spyCanVerifyInvokedParameters() {
  XCTAssertEqual(animatorSpy.invokedAnimateParameters?.duration, 5)

Test the number of times animate was invoked:

func test_spyCanVerifyInvokedMethodCount() {
  XCTAssertEqual(animatorSpy.invokedAnimateCount, 2)

Test the parameters passed into each call of the animate method:

func test_spyCanVerifyMultipleInvokedMethodParameters() {
  XCTAssertEqual(animatorSpy.invokedAnimateParametersList[0].duration, 5)
  XCTAssertEqual(animatorSpy.invokedAnimateParametersList[1].duration, 5)

Stub a return value for the animate method:

func test_spyCanReturnAStubbedValue() {
  animatorSpy.stubbedAnimateResult = true
  let result = object.myMethod()

Stub the value for the completion closure in the animate method:

func test_spyCanCallClosure_withStubbedValue() {
  animatorSpy.stubbedAnimateCompletionResult = (false, ())

What is a spy?

Spies are stubs that also record some information based on how they were called. One form of this might be an email service that records how many messages it was sent. See reference

What is a stub?

Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. See reference

What is a dummy?

Dummy objects are passed around but never actually used. Usually they are just used to fill parameter lists. See reference

What is a partial spy?

Partial spies are spies which can also forward calls to the original implementation.

Disable or remove the plugin

To disable:

Go to System Preferences -> Extensions and deselect the extension under Xcode Source Editor.

To remove:

Delete the app.


Despite being called a Mock Generator, this plugin actually generates a spy, stub or dummy. The word 'mock', whilst not technically correct, has been used because test doubles such as spies, mocks, and stubs have become commonly known as mocks.


This project currently depends on some private libraries so it cannot currently be built by a third party.


Many thanks to the contributors of SourceKitten for making such an easy-to-use wrapper around SourceKit.

Many thanks to the contributors of swift-ast for a great lexer which has made writing a parser much easier.

Many thanks to the contributors of kotlin-native for a Kotlin LLVM backend which enables code sharing between the Xcode and AppCode plugins.

Many thanks to the contributors of GRMustache for a enabling great Mustache test double templates.

And special thanks to everyone who is contributing by raising issues and feature requests.

This tool wouldn't exist without you all!