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API mocking framework for iOS projects that allows localized and quick unit and UI tests
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swift-mimic.podspec Release 0.3.0 Jan 15, 2019

Version License Platform Swift 4.2


Swift-Mimic is a library for mocking network requests with minimal code changes. It can be used for:

  • Converting unit tests and UI tests to run on mocked API responses, minimizing test maintenance and optimizing tests for speed
  • Developing new features before actual API endpoints are ready, with minimal code changes

Swift-Mimic is designed to be a batteries included, easy-to-integrate solution with several extensible features:

  • File-based mock bundles that reflect the API endpoint structures, coupled with a base URL
  • Support for multiple mock bundle suites, cascading with overrides for different test scenarios
  • Swappable mock bundle protocol so you can develop your own advanced bundle formats if needed
  • Automated endpoint discovery from mock bundles, so default scenarios require no code
  • Integration with any existing unit or UI test using three lines of code


We recommend using Cocoapods for installing:

pod 'swift-mimic'

IMPORTANT: Due to a known Cocoapods issue, UI tests might fail to compile. Documented solution for now is to include the following post_install hook in your Podfile:

post_install do |installer|
    installer.pods_project.targets.each do |target|
        target.build_configurations.each do |config|
            # This works around a unit test issue introduced in Xcode 10.
            # We only apply it to the Debug configuration to avoid bloating the app size
            if == "Debug" && defined?(target.product_type) && target.product_type == ""
                config.build_settings['ALWAYS_EMBED_SWIFT_STANDARD_LIBRARIES'] = "YES"


Creating Mock Bundles

First step before configuring your application to use Swift-Mimic is to create an API mock bundle. There are several ways of doing this, from manually generating the folder and file structure to using a recorder framework such as SWHttpTrafficRecorder.

Structure of the mock bundle is simple. Let's assume that you have an API that provides the following endpoints:

And let's assume that you will be mocking the following requests:

Your mock bundle structure should then look like this:

  • Mocks.bundle
    • api
      • authenticate
        • post.json
      • users
        • get.json
      • projects
        • get_200.json
        • post_201.json

Every JSON file in this list should contain the API response that should be mocked. File names can be provided in two formats: HTTP METHOD.json or HTTP METHOD_RESPONSE CODE.json. If you don't provide a response code, Swift-Mock will assume that the matching HTTP method is the default file and will prioritize that over others.

You may add the bundle anywhere in your Xcode project, however make sure that it's linked against both your main application target, as well as your test target.

You may create as many bundles as you like, to either organize endpoints under a single base URL or support mocks under multiple API URLs.

Updating Network Integration

For Swift-Mimic to override network requests without additional code, you need to pass a special configuration to the active URLSession your API requests layer uses. This is very easy to do, here is an example that uses Alamofire:

if let mockUrlSessionConfiguration = MimicSession.shared?.urlSessionConfiguration {
  sessionManager = Alamofire.SessionManager(configuration: mockUrlSessionConfiguration)
} else {
  sessionManager =  SessionManager.default

This is a standard URLSessionConfiguration object, so it can be passed to any network layer that runs on URLSession, including Apple's vanilla implementation.

Setting Up Test Suites

Final step is to define your mock suites in your testing layer so the test runner is launched aware of the mocks it is configured with. Here is the simplest implementation you can do:

import XCTest
import swift_mimic

extension XCUIApplication: MimicUIApplication {

class ExampleTest: XCTestCase {

    var app: XCUIApplication = XCUIApplication()
    override func setUp() {
        continueAfterFailure = false

        let suite = MIMMockSuite(baseURL: "", bundleNames: "Mocks")

        try? MimicLauncher.launch(app, with: [suite])


There are a few things happening here. First off, we make sure that the XCUIApplication is setup to include MimicUIApplication. You need to do this only once somewhere in your test target.

Then we create a MIMMockSuite instance that points to the correct bundle in the project and pairs it with the API base URL we would like to override.

Finally, we call MimicLauncher with the suite we just created, so it can include it in the configuration.

You can create as many suites as you like, and pass them to the launcher in the order you would like them to be loaded in. Let's say you have a specific authentication case for a test suite. If different base URLs are required for the case, you could do the following to take advantage of the cascading nature of suites:

class ExampleTest: XCTestCase {

    var app: XCUIApplication = XCUIApplication()
    override func setUp() {
        let suite = MIMMockSuite(baseURL: "", bundleNames: "Mocks")
        let adminSuite = MIMMockSuite(baseURL: "", bundleNames: "AdminMocks")

        try? MimicLauncher.launch(app, with: [suite, adminSuite])


If you have same base URL for both cases, you should use the following structure:

class ExampleTest: XCTestCase {

    var app: XCUIApplication = XCUIApplication()

    override func setUp() {
        let suite = MIMMockSuite(baseURL: "", bundleNames: ["Mocks", "AdminMocks"])

        try? MimicLauncher.launch(app, with: [suite])


Suites will be prioritized from the last element to the first element of array, in descending order.

Release History

  • 0.3.0 - Jan 15, 2019
    • Add auto-discovery and easier basic setup
  • 0.2.5 - Jan 14, 2019
    • Add documentation
  • 0.2.3 - Jan 13, 2019
    • First stable release with complete sample project


Built by the Hipo team, with contributions by:

  • Goktug Berk Ulu
  • Eray Diler
  • Salih Karasuluoglu
  • Taylan Pince


  1. Fork it (
  2. Create your feature branch (git checkout -b feature/fooBar)
  3. Commit your changes (git commit -am 'Add some fooBar')
  4. Push to the branch (git push origin feature/fooBar)
  5. Create a new Pull Request


Distributed under the MIT license. See LICENSE for more information.

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