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A Swift DSL for creating pact contracts implementing Pact Specification Version 3.


Release: pre-BETA MIT License PRs Welcome! slack Twitter codecov Build

PactSwift logo

This framework provides a Swift DSL for generating Pact contracts.

It implements Pact Specification v3 and takes advantage of libpact_mock_server running it "in process".

⚠️ NOTE ⚠️
PactSwift is under heavy development. We are specifically looking into supporting arm64, arm64e alongside x86_64.
Any and all help with testing, raising issues and suggestions for improvement is more than welcome.

Due to the new Apple Silicon architecture and required tools' limited support for arm64 and arm64e architecture, PactSwift works on macOS x86_64 machines but running it on arch64-darwin machines might be broken, for now!
Any and all help finding a working solution is more than welcome. See #52.


PactSwift uses pact_mock_server_ffi written in Rust-lang as a git submodule. It builds a binary during a PactSwift Build Phase and requires Rust installed on your machine:

brew install rust
cargo install cargo-lipo

or follow installation instructions available at rust-lang.

The first time PactSwift is built on your machine it will take quite a long time due to also compiling the Rust binary. As long as the compiled binary exists in the Rust build folder, it will skip re-compiling it and build times should be much shorter.



github "surpher/PactSwift" ~> 0.3

Please note Carthage is not too happy with Xcode 12 - https://github.com/surpher/PactSwift/issues/27.

Swift Package Manager

dependencies: [
    .package(url: "https://github.com/surpher/PactSwift.git", .upToNextMajor(from: "0.3.0"))

Due to limitations of sharing binaries through SPM and the size of the compiled binaries there are a few extra steps to be made in order to use PactSwift with SPM!

See pact-swift-examples for an example on how to set it up for Xcode and CI/CD.

Xcode setup - Carthage

This framework is intended to be used in your test target only! Do not embed it into your app bundle!

Setup Framework Build Settings

Framework Search Paths

In your test targets build settings, update Framework Search Paths configuration to include $(PROJECT_DIR)/Carthage/Build/iOS (non-recursive):


Runpath Search Paths

In your test targets build settings, update Runpath Search Paths configuration to include $(FRAMEWORK_SEARCH_PATHS):


Xcode setup - Swift Package Manager

Set PactSwift as a Swift Package

swift package

Define a Build Step Run Script

Set write permissions for Xcode to replace the fake binaries with the one compiled by your machine. Use the PactSwift/Scripts/BuildPhases/build-spm-dependency script in the package folder:

build step

Make sure you set the PATH with location of your cargo and rustup.

Edit search paths

Add $BUILD_DIR/../../SourcePackages/checkouts/PactSwift/Resources -recursive to Library Search Paths and Frameworks Search Paths in your test target's build settings.

library search path

PactSwift Environment variables

Edit your scheme and add PACT_OUTPUT_DIR environment variable (Run step) with path to the directory you want your Pact contracts to be written to. By default, Pact contracts are written to /tmp/pacts.

⚠️ Sandboxed apps are limited in where they can write the Pact contract file. The default location is the Documents folder in the sandbox (eg: ~/Library/Containers/com.example.your-project-name/Data/Documents) and can not be overriden by the environment variable PACT_OUTPUT_DIR. Look at the logs in debug area for the Pact file location.

To enable logging, edit your scheme and add PACT_ENABLE_LOGGING: true to capture telemetry for debugging analysis using the unified logging system.


Writing Pact tests

  • Instantiate a MockService object by defining pacticipants,
  • Define the state of the provider for an interaction (one Pact test),
  • Define the expected request for the interaction,
  • Define the expected response for the interaction,
  • Run the test by making the API request using your API client and assert what you need asserted,
  • Share the generated Pact contract file with your provider (eg: upload to a Pact Broker),
  • Run can-i-deploy (eg: on your CI/CD) to deploy with confidence.

Example Test

import XCTest
import PactSwift

@testable import ExampleProject

class PassingTestsExample: XCTestCase {

  var mockService = MockService(consumer: "Example-iOS-app", provider: "some-service")

  // MARK: - Tests

  func testGetUsers() {
    // #1 - Define the API contract by configuring how `mockService`, and consequently the "real" API, will behave for this specific API request we are testing here

      // #2 - Define the interaction description and provider state for this specific API request that we are testing
      .uponReceiving("A request for a list of users")
      .given(ProviderState(description: "users exist", params: ["first_name": "John", "last_name": "Tester"])

      // #3 - Define the request we promise our API consumer will make
        method: .GET,
        path: "/api/users",
        headers: nil, // `nil` means we (and the API Provider) should not care about headers. If there are values there, fine, we're just not _demanding_ anything.
        body: nil // same as with headers

      // #4 - Define what we expect `mockService`, and consequently the "real" API, to respond with for this particular API request we are testing
        status: 200,
        headers: nil, // `nil` means we don't care what the headers returned from the API are. If there are values in the header, fine, we're just not _demanding_ anything in the header.
        body: [
          "page": Matcher.SomethingLike(1), // We will use matchers here, as we normally care about the types and structure, not necessarily the actual value.
          "per_page": Matcher.SomethingLike(20),
          "total": ExampleGenerator.RandomInt(min: 20, max: 500),
          "total_pages": Matcher.SomethingLike(3),
          "data": Matcher.EachLike(
              "id": ExampleGenerator.RandomUUID(), // We can also use example generators with Pact Spec v3
              "first_name": Matcher.SomethingLike("John"),
              "last_name": Matcher.SomethingLike("Tester"),
              "salary": Matcher.DecimalLike(125000.00)

    // #5 - Fire up our API client
    let apiClient = RestManager()

    // Run a Pact test and assert **our** API client makes the request exactly as we promised above
    mockService.run(waitFor: 1) { [unowned self] completed in

      // #6 - _Redirect_ your API calls to the address MockService runs on - replace base URL, but path should be the same
      apiClient.baseUrl = self.mockService.baseUrl

      // #7 - Make the API request.
      apiClient.getUsers() { users in

          // #8 - Test that **our** API client handles the response as expected. (eg: `getUsers() -> [User]`)
          XCTAssertEqual(users.count, 20)
          XCTAssertEqual(users.first?.firstName, "John")
          XCTAssertEqual(users.first?.lastName, "Tester")

        // #9 - Notify MockService we're done with our test, else your Pact test will time out.

  // More tests for other interactions and/or provider states...
  func testCreateUser() {
      .uponReceiving("A request to create a user")
      .given(ProviderState(description: "user does not exist", params: ["first_name": "John", "last_name": "Appleseed"])
        method: .POST,
        path: Matcher.RegexLike("/api/group/whoopeedeedoodah/users", term: #"^/\w+/group/([a-z])+/users$"#),
        body: [
          "first_name": "John",
          "last_name": "Appleseed",
          "age": Matcher.SomethingLike(42),
          "dob": Matcher.RegexLike("15-07-2001", term: #"\d{2}-\d{2}-\d{4}"#),
          "trivia": [
            "favourite_words": Matcher.EachLike("foo"),
            "bar": Matcher.IncludesLike("baz")
        status: 201

   let apiClient = RestManager()

    mockService.run { completed in
     // trigger your network request and assert the expectations
  // etc.


In addition to verbatim value matching, you can use a set of useful matching objects that can increase expressiveness and reduce brittle test cases.

See Wiki page about Matchers for a list of matchers PactSwift implements and their basic usage.

Or peek into /Sources/Matchers/.

Example Generators

In addition to verbatim value matching and some helpful matchers, you can use a set of example generators that generate random values each time you run your tests.

In some cases, dates and times may need to be relative to the current date and time, and some things like tokens may have a very short life span.

Example generators help you generate random values and define the rules around them.

See Wiki page about Example Generators for a list of example generators PactSwift implements and their basic usage.

Or peek into /Sources/ExampleGenerators/.

Verifying your client against the service you are integrating with

If you set the PACT_OUTPUT_DIR environment variable, your Xcode setup is correct and your tests successfully run, then you should see the generated Pact files in: $(PACT_OUTPUT_DIR)/_consumer_name_-_provider_name_.json.

Publish your generated Pact file(s) to your Pact Broker or a hosted service, so that your API-provider team can always retrieve them from one location, even when pacts change. Normally you do this regularly in you CI step/s.

See how you can use simple Pact Broker Client in your terminal (CI/CD) to upload and tag your Pact files. And most importantly check if you can safely deploy a new version of your app.

Objective-C support

PactSwift can be used in your Objective-C project with a couple of limitations, e.g. initializers with multiple optional arguments are limited to only one or two available initializers. See Demo projects repository for examples of Pact tests written in Objective-C.

Demo projects

See pact-swift-examples repo.

Project Status Dependency manager
iOS Test iOS project Carthage
iOS (Objective-C) Test iOS (Objective-C) project Carthage
iOS Test iOS (SPM) project Swift Package Manager
macOS Test macOS project Carthage
macOS Test macOS (SPM) project Swift Package Manager




This project takes inspiration from pact-consumer-swift and pull request Feature/native wrapper PR.

Logo and branding images provided by @cjmlgrto.


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