SwiftCheck

SwiftCheck is a free, MIT-licensed property-testing library for Swift developers. Its `forAll` quantifier lets tests describe properties that should hold across generated inputs, and its README demonstrates using those properties inside an `XCTestCase`. When a generated case fails, SwiftCheck shrinks the input toward a smaller counterexample. The library implements `Arbitrary` for most Swift Standard Library types, while custom types can participate by supplying generation and shrinking behavior. Generator combinators include `suchThat`, `fromElements`, `choose`, and `frequency`. Properties can be combined with conjunction and labels, and can use preconditions to discard inputs that do not apply. Installation options include Swift Package Manager, Carthage, CocoaPods, or adding the Xcode project as a framework dependency. The listed system requirements are OS X 10.9+ and iOS 7.0+. The repository links issue tracking and contribution guidance, but does not state a support service or security certification.

SwiftCheck provides generated-input property testing with shrinking and several installation paths. Its documented system requirements are older OS X and iOS versions, so developers should check those against their project needs.

Swift developers who want to express tests as properties over generated inputs may find it useful, particularly those using XCTest. It also accommodates custom types when developers provide generation and shrinking behavior.

SwiftCheck is a free property-testing library for Swift developers who want to check behavior across automatically generated inputs, not just hand-picked examples. Its strongest fit is an XCTest workflow that benefits from shrinking failures to smaller counterexamples; teams that need a newer baseline than its documented OS X 10.9 and iOS 7.0 support should verify compatibility first.

Overview

Instead of writing only individual test cases, developers can express a property that should hold across many inputs with the forAll quantifier. SwiftCheck generates values and, when a case fails, shrinks them toward a minimal counterexample. That combination can make broad input coverage more useful to diagnose than a failure on a large, unwieldy test value.

The library is MIT-licensed and supports Swift. Its README demonstrates properties within an XCTestCase, so it suits projects already using Apple’s XCTest framework without requiring a separate runner in the documented example.

Key features

Generated inputs and failure shrinking

SwiftCheck implements Arbitrary for most Swift Standard Library types and Testable for Bool and related types. Developers can also make custom types Arbitrary by defining how they are generated and shrunk. Shrinking is a practical advantage when a randomly generated failure is complex: it aims to reduce the input to a more manageable counterexample. Custom types require that generation and shrinking behavior to be supplied.

Generators and composed properties

Generator combinators include suchThat, fromElements, choose, and frequency. Properties can be combined with conjunction and labels, and preconditions can discard inputs that do not meet a condition. These tools make the library more adaptable than a fixed set of built-in examples, though the developer remains responsible for defining meaningful properties and custom generators.

Pricing

SwiftCheck is free, with a free plan at no cost. There is no free trial because there is no paid plan described; no seat or usage quota is stated. The MIT license also permits use under its open-source terms. This is a straightforward fit for individual developers and teams seeking a no-cost Swift property-testing library, rather than a commercial testing service.

Platforms

SwiftCheck supports iOS and macOS. Its documented requirements are OS X 10.9+ and iOS 7.0+. Developers targeting other Apple operating systems or newer project-specific deployment needs should confirm that those requirements align before adopting it. The README gives four integration paths: Swift Package Manager, Carthage, CocoaPods, or adding the Xcode project as a framework dependency. That breadth gives existing projects more than one way to incorporate the library.

Who it's for

SwiftCheck is best for Swift developers who want generated-input property tests within XCTest and value reduced counterexamples when a property fails. It is less suitable when a project cannot accommodate its documented platform requirements, or when a team wants a stated support service or security certification; neither is described for the project.

Pros and cons

• Pros: Generated tests cover inputs beyond manually selected cases, while shrinking can make failing cases easier to inspect.
• Pros: Most Swift Standard Library types are supported through Arbitrary, and custom types can participate with their own generation and shrinking behavior.
• Pros: XCTest examples and four installation routes can fit different existing Swift project setups.
• Cons: Custom types need developer-supplied generation and shrinking rules, adding setup work where built-in types are not enough.
• Cons: Its published OS X and iOS requirements are old baselines, so compatibility still needs checking against a project's targets.

Alternatives

For a broader comparison, browse Property-Based Testing Tools. Swift developers seeking alternatives in another language can consider Gopter, a free MIT-licensed Go property-testing library, or JSVerify, a free open-source JavaScript property-based testing library. Scala teams can choose Scala Hedgehog, a free open-source Scala testing library, or ScalaCheck, a free BSD-3-Clause library with Linux, macOS, and Windows platforms.

For other language ecosystems, CsCheck is free under Apache 2; FsCheck is a free BSD-licensed library distributed through NuGet packages; PropCheck is a free MIT-licensed Ruby gem requiring Ruby 2.5.1 or later; and QCheck is a free OCaml property-testing library under BSD-2-Clause. These are options to consider when the language or package ecosystem matters more than Swift/XCTest integration.

Verdict

SwiftCheck is a strong choice for Swift developers who want free, generated-input property tests in an XCTest-oriented workflow, especially when shrinking can clarify failures. Choose it for that focused capability; look elsewhere if its documented platform requirements do not suit the project or if the team needs a stated support service or security certification.