Nimble

Use Nimble to express the expected outcomes of Swift or Objective-C expressions. Inspired by Cedar.

// Swift
expect(1 + 1).to(equal(2))
expect(1.2).to(beCloseTo(1.1, within: 0.1))
expect(3) > 2
expect("seahorse").to(contain("sea"))
expect(["Atlantic", "Pacific"]).toNot(contain("Mississippi"))
expect(ocean.isClean).toEventually(beTruthy())

How to Use Nimble

Table of Contents generated with DocToc

• Some Background: Expressing Outcomes Using Assertions in XCTest
• Nimble: Expectations Using expect(...).to
  • Custom Failure Messages
  • Type Safety
  • Operator Overloads
  • Lazily Computed Values
  • C Primitives
  • Async/Await in Expectations
  • Polling Expectations
  • Objective-C Support
  • Disabling Objective-C Shorthand
• Built-in Matcher Functions
  • Type Checking
  • Equivalence
  • Identity
  • Comparisons
  • Types/Classes
  • Truthiness
  • Swift Assertions
  • Swift Error Handling
  • Exceptions
  • Collection Membership
  • Strings
  • Collection Elements
  • Collection Count
  • Notifications
  • Result
  • Matching a value to any of a group of matchers
  • Custom Validation
• Writing Your Own Matchers
  • PredicateResult
  • Lazy Evaluation
  • Type Checking via Swift Generics
  • Customizing Failure Messages
    • Basic Customization
    • Full Customization
  • Supporting Objective-C
    • Properly Handling nil in Objective-C Matchers
  • Migrating from the Old Matcher API
• Installing Nimble
  • Installing Nimble as a Submodule
  • Installing Nimble via CocoaPods
  • Using Nimble without XCTest

Some Background: Expressing Outcomes Using Assertions in XCTest

Apple's Xcode includes the XCTest framework, which provides assertion macros to test whether code behaves properly. For example, to assert that 1 + 1 = 2, XCTest has you write:

// Swift

XCTAssertEqual(1 + 1, 2, "expected one plus one to equal two")

Or, in Objective-C:

// Objective-C

XCTAssertEqual(1 + 1, 2, @"expected one plus one to equal two");

XCTest assertions have a couple of drawbacks:

1. Not enough macros. There's no easy way to assert that a string contains a particular substring, or that a number is less than or equal to another.
2. It's hard to write asynchronous tests. XCTest forces you to write a lot of boilerplate code.

Nimble addresses these concerns.

Nimble: Expectations Using expect(...).to

Nimble allows you to express expectations using a natural, easily understood language:

// Swift

import Nimble

expect(seagull.squawk).to(equal("Squee!"))

// Objective-C

@import Nimble;

expect(seagull.squawk).to(equal(@"Squee!"));

The expect function autocompletes to include file: and line:, but these parameters are optional. Use the default values to have Xcode highlight the correct line when an expectation is not met.

To perform the opposite expectation--to assert something is not equal--use toNot or notTo:

// Swift

import Nimble

expect(seagull.squawk).toNot(equal("Oh, hello there!"))
expect(seagull.squawk).notTo(equal("Oh, hello there!"))

// Objective-C

@import Nimble;

expect(seagull.squawk).toNot(equal(@"Oh, hello there!"));
expect(seagull.squawk).notTo(equal(@"Oh, hello there!"));

Custom Failure Messages

Would you like to add more information to the test's failure messages? Use the description optional argument to add your own text:

// Swift

expect(1 + 1).to(equal(3))
// failed - expected to equal <3>, got <2>

expect(1 + 1).to(equal(3), description: "Make sure libKindergartenMath is loaded")
// failed - Make sure libKindergartenMath is loaded
// expected to equal <3>, got <2>

Or the *WithDescription version in Objective-C:

// Objective-C

@import Nimble;

expect(@(1+1)).to(equal(@3));
// failed - expected to equal <3.0000>, got <2.0000>

expect(@(1+1)).toWithDescription(equal(@3), @"Make sure libKindergartenMath is loaded");
// failed - Make sure libKindergartenMath is loaded
// expected to equal <3.0000>, got <2.0000>

Type Safety

Nimble makes sure you don't compare two types that don't match:

// Swift

// Does not compile:
expect(1 + 1).to(equal("Squee!"))

Nimble uses generics--only available in Swift--to ensure type correctness. That means type checking is not available when using Nimble in Objective-C. 😭

Operator Overloads

Tired of so much typing? With Nimble, you can use overloaded operators like == for equivalence, or > for comparisons:

// Swift

// Passes if squawk does not equal "Hi!":
expect(seagull.squawk) != "Hi!"

// Passes if 10 is greater than 2:
expect(10) > 2

Operator overloads are only available in Swift, so you won't be able to use this syntax in Objective-C. 💔

Lazily Computed Values

The expect function doesn't evaluate the value it's given until it's time to match. So Nimble can test whether an expression raises an exception once evaluated:

// Swift

// Note: Swift currently doesn't have exceptions.
//       Only Objective-C code can raise exceptions
//       that Nimble will catch.
//       (see https://github.com/Quick/Nimble/issues/220#issuecomment-172667064)
let exception = NSException(
    name: NSInternalInconsistencyException,
    reason: "Not enough fish in the sea.",
    userInfo: ["something": "is fishy"])
expect { exception.raise() }.to(raiseException())

// Also, you can customize raiseException to be more specific
expect { exception.raise() }.to(raiseException(named: NSInternalInconsistencyException))
expect { exception.raise() }.to(raiseException(
    named: NSInternalInconsistencyException,
    reason: "Not enough fish in the sea"))
expect { exception.raise() }.to(raiseException(
    named: NSInternalInconsistencyException,
    reason: "Not enough fish in the sea",
    userInfo: ["something": "is fishy"]))

Objective-C works the same way, but you must use the expectAction macro when making an expectation on an expression that has no return value:

// Objective-C

NSException *exception = [NSException exceptionWithName:NSInternalInconsistencyException
                                                 reason:@"Not enough fish in the sea."
                                               userInfo:nil];
expectAction(^{ [exception raise]; }).to(raiseException());

// Use the property-block syntax to be more specific.
expectAction(^{ [exception raise]; }).to(raiseException().named(NSInternalInconsistencyException));
expectAction(^{ [exception raise]; }).to(raiseException().
    named(NSInternalInconsistencyException).
    reason("Not enough fish in the sea"));
expectAction(^{ [exception raise]; }).to(raiseException().
    named(NSInternalInconsistencyException).
    reason("Not enough fish in the sea").
    userInfo(@{@"something": @"is fishy"}));

// You can also pass a block for custom matching of the raised exception
expectAction(exception.raise()).to(raiseException().satisfyingBlock(^(NSException *exception) {
    expect(exception.name).to(beginWith(NSInternalInconsistencyException));
}));

C Primitives

Some testing frameworks make it hard to test primitive C values. In Nimble, it just works:

// Swift

let actual: CInt = 1
let expectedValue: CInt = 1
expect(actual).to(equal(expectedValue))

In fact, Nimble uses type inference, so you can write the above without explicitly specifying both types:

// Swift

expect(1 as CInt).to(equal(1))

In Objective-C, Nimble only supports Objective-C objects. To make expectations on primitive C values, wrap then in an object literal:

expect(@(1 + 1)).to(equal(@2));

Async/Await Support

Nimble makes it easy to await for an async function to complete. Simply pass the async function in to expect:

// Swift
await expect { await aFunctionReturning1() }.to(equal(1))

The async function is awaited on first, before passing it to the matcher. This enables the matcher to run synchronous code like before, without caring about whether the value it's processing was abtained async or not.

Async support is Swift-only, and it requires that you execute the test in an async context. For XCTest, this is as simple as marking your test function with async. If you use Quick, then you don't need to do anything because as of Quick 6, all tests are executed in an async context.

To avoid a compiler errors when using synchronous expect in asynchronous contexts, expect with async expressions does not support autoclosures. However, the expecta (expect async) function is provided as an alternative, which does support autoclosures.

// Swift
await expect(await aFunctionReturning1()).to(equal(1)))

Similarly, if you're ever in a situation where you want to force the compiler to produce a SyncExpectation, you can use the expects (expect sync) function to produce a SyncExpectation. Like so:

// Swift
expects(someNonAsyncFunction()).to(equal(1)))

expects(await someAsyncFunction()).to(equal(1)) // Compiler error: 'async' call in an autoclosure that does not support concurrency

Note: Async/Await support is different than the toEventually/toEventuallyNot feature described below.

Polling Expectations

In Nimble, it's easy to make expectations on values that are updated asynchronously. Just use toEventually or toEventuallyNot:

// Swift
DispatchQueue.main.async {
    ocean.add("dolphins")
    ocean.add("whales")
}
expect(ocean).toEventually(contain("dolphins", "whales"))

// Objective-C

dispatch_async(dispatch_get_main_queue(), ^{
    [ocean add:@"dolphins"];
    [ocean add:@"whales"];
});
expect(ocean).toEventually(contain(@"dolphins", @"whales"));

Note: toEventually triggers its polls on the main thread. Blocking the main thread will cause Nimble to stop the run loop. This can cause test pollution for whatever incomplete code that was running on the main thread. Blocking the main thread can be caused by blocking IO, calls to sleep(), deadlocks, and synchronous IPC.

In the above example, ocean is constantly re-evaluated. If it ever contains dolphins and whales, the expectation passes. If ocean still doesn't contain them, even after being continuously re-evaluated for one whole second, the expectation fails.

toEventaully et. al. now also supports async expectations. For example, the following test is now supported:

actor MyActor {
    private var counter = 0

    func access() -> Int {
        counter += 1
        return counter
    }
}

let subject = MyActor()
await expect { await subject.access() }.toEventually(equal(2))

You can also test that a value always or never matches throughout the length of the timeout. Use toNever and toAlways for this:

// Swift
ocean.add("dolphins")
expect(ocean).toAlways(contain("dolphins"))
expect(ocean).toNever(contain("hares"))

// Objective-C
[ocean add:@"dolphins"]
expect(ocean).toAlways(contain(@"dolphins"))
expect(ocean).toNever(contain(@"hares"))

Sometimes it takes more than a second for a value to update. In those cases, use the timeout parameter:

// Swift

// Waits three seconds for ocean to contain "starfish":
expect(ocean).toEventually(contain("starfish"), timeout: .seconds(3))

// Evaluate someValue every 0.2 seconds repeatedly until it equals 100, or fails if it timeouts after 5.5 seconds.
expect(someValue).toEventually(equal(100), timeout: .milliseconds(5500), pollInterval: .milliseconds(200))

// Objective-C

// Waits three seconds for ocean to contain "starfish":
expect(ocean).withTimeout(3).toEventually(contain(@"starfish"));

You can also provide a callback by using the waitUntil function:

// Swift

waitUntil { done in
    ocean.goFish { success in
        expect(success).to(beTrue())
        done()
    }
}

// Objective-C

waitUntil(^(void (^done)(void)){
    [ocean goFishWithHandler:^(BOOL success){
        expect(success).to(beTrue());
        done();
    }];
});

waitUntil also optionally takes a timeout parameter:

// Swift

waitUntil(timeout: .seconds(10)) { done in
    ocean.goFish { success in
        expect(success).to(beTrue())
        done()
    }
}

// Objective-C

waitUntilTimeout(10, ^(void (^done)(void)){
    [ocean goFishWithHandler:^(BOOL success){
        expect(success).to(beTrue());
        done();
    }];
});

Note: waitUntil triggers its timeout code on the main thread. Blocking the main thread will cause Nimble to stop the run loop to continue. This can cause test pollution for whatever incomplete code that was running on the main thread. Blocking the main thread can be caused by blocking IO, calls to sleep(), deadlocks, and synchronous IPC.

Changing default Timeout and Poll Intervals

In some cases (e.g. when running on slower machines) it can be useful to modify the default timeout and poll interval values. This can be done as follows:

// Swift

// Increase the global timeout to 5 seconds:
Nimble.PollingDefaults.timeout = .seconds(5)

// Slow the polling interval to 0.1 seconds:
Nimble.PollingDefaults.pollInterval = .milliseconds(100)

You can set these globally at test startup in two ways:

Quick

If you use Quick, add a QuickConfiguration subclass which sets your desired PollingDefaults.

import Quick
import Nimble

class PollingConfiguration: QuickConfiguration {
    override class func configure(_ configuration: QCKConfiguration) {
        Nimble.PollingDefaults.timeout = .seconds(5)
        Nimble.PollingDefaults.pollInterval = .milliseconds(100)
    }
}

XCTest

If you use XCTest, add an object that conforms to XCTestObservation and implement testBundleWillStart(_:).

Additionally, you will need to register this observer with the XCTestObservationCenter at test startup. To do this, set the NSPrincipalClass key in your test bundle's Info.plist and implement a class with that same name.

For example

<!-- Info.plist -->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <!-- ... -->
	<key>NSPrincipalClass</key>
	<string>MyTests.TestSetup</string>
</dict>
</plist>

// TestSetup.swift
import XCTest
import Nimble

@objc
class TestSetup: NSObject {
	override init() {
		XCTestObservationCenter.shared.register(PollingConfigurationTestObserver())
	}
}

class PollingConfigurationTestObserver: NSObject, XCTestObserver {
    func testBundleWillStart(_ testBundle: Bundle) {
        Nimble.PollingDefaults.timeout = .seconds(5)
        Nimble.PollingDefaults.pollInterval = .milliseconds(100)
    }
}

In Linux, you can implement LinuxMain to set the PollingDefaults before calling XCTMain.

Objective-C Support

Nimble has full support for Objective-C. However, there are two things to keep in mind when using Nimble in Objective-C:

1. All parameters passed to the expect function, as well as matcher functions like equal, must be Objective-C objects or can be converted into an NSObject equivalent:

   // Objective-C
   
   @import Nimble;
   
   expect(@(1 + 1)).to(equal(@2));
   expect(@"Hello world").to(contain(@"world"));
   
   // Boxed as NSNumber *
   expect(2).to(equal(2));
   expect(1.2).to(beLessThan(2.0));
   expect(true).to(beTruthy());
   
   // Boxed as NSString *
   expect("Hello world").to(equal("Hello world"));
   
   // Boxed as NSRange
   expect(NSMakeRange(1, 10)).to(equal(NSMakeRange(1, 10)));

2. To make an expectation on an expression that does not return a value, such as -[NSException raise], use expectAction instead of expect:

   // Objective-C
   
   expectAction(^{ [exception raise]; }).to(raiseException());

The following types are currently converted to an NSObject type:

• C Numeric types are converted to NSNumber *
• NSRange is converted to NSValue *
• char * is converted to NSString *

For the following matchers:

• equal
• beGreaterThan
• beGreaterThanOrEqual
• beLessThan
• beLessThanOrEqual
• beCloseTo
• beTrue
• beFalse
• beTruthy
• beFalsy
• haveCount

If you would like to see more, file an issue.

Disabling Objective-C Shorthand

Nimble provides a shorthand for expressing expectations using the expect function. To disable this shorthand in Objective-C, define the NIMBLE_DISABLE_SHORT_SYNTAX macro somewhere in your code before importing Nimble:

#define NIMBLE_DISABLE_SHORT_SYNTAX 1

@import Nimble;

NMB_expect(^{ return seagull.squawk; }, __FILE__, __LINE__).to(NMB_equal(@"Squee!"));

Disabling the shorthand is useful if you're testing functions with names that conflict with Nimble functions, such as expect or equal. If that's not the case, there's no point in disabling the shorthand.

Built-in Matcher Functions

Nimble includes a wide variety of matcher functions.

Type Checking

Nimble supports checking the type membership of any kind of object, whether Objective-C conformant or not:

// Swift

protocol SomeProtocol{}
class SomeClassConformingToProtocol: SomeProtocol{}
struct SomeStructConformingToProtocol: SomeProtocol{}

// The following tests pass
expect(1).to(beAKindOf(Int.self))
expect("turtle").to(beAKindOf(String.self))

let classObject = SomeClassConformingToProtocol()
expect(classObject).to(beAKindOf(SomeProtocol.self))
expect(classObject).to(beAKindOf(SomeClassConformingToProtocol.self))
expect(classObject).toNot(beAKindOf(SomeStructConformingToProtocol.self))

let structObject = SomeStructConformingToProtocol()
expect(structObject).to(beAKindOf(SomeProtocol.self))
expect(structObject).to(beAKindOf(SomeStructConformingToProtocol.self))
expect(structObject).toNot(beAKindOf(SomeClassConformingToProtocol.self))

// Objective-C

// The following tests pass
NSMutableArray *array = [NSMutableArray array];
expect(array).to(beAKindOf([NSArray class]));
expect(@1).toNot(beAKindOf([NSNull class]));

Objects can be tested for their exact types using the beAnInstanceOf matcher:

// Swift

protocol SomeProtocol{}
class SomeClassConformingToProtocol: SomeProtocol{}
struct SomeStructConformingToProtocol: SomeProtocol{}

// Unlike the 'beKindOf' matcher, the 'beAnInstanceOf' matcher only
// passes if the object is the EXACT type requested. The following
// tests pass -- note its behavior when working in an inheritance hierarchy.
expect(1).to(beAnInstanceOf(Int.self))
expect("turtle").to(beAnInstanceOf(String.self))

let classObject = SomeClassConformingToProtocol()
expect(classObject).toNot(beAnInstanceOf(SomeProtocol.self))
expect(classObject).to(beAnInstanceOf(SomeClassConformingToProtocol.self))
expect(classObject).toNot(beAnInstanceOf(SomeStructConformingToProtocol.self))

let structObject = SomeStructConformingToProtocol()
expect(structObject).toNot(beAnInstanceOf(SomeProtocol.self))
expect(structObject).to(beAnInstanceOf(SomeStructConformingToProtocol.self))
expect(structObject).toNot(beAnInstanceOf(SomeClassConformingToProtocol.self))

Equivalence

// Swift

// Passes if 'actual' is equivalent to 'expected':
expect(actual).to(equal(expected))
expect(actual) == expected

// Passes if 'actual' is not equivalent to 'expected':
expect(actual).toNot(equal(expected))
expect(actual) != expected

// Objective-C

// Passes if 'actual' is equivalent to 'expected':
expect(actual).to(equal(expected))

// Passes if 'actual' is not equivalent to 'expected':
expect(actual).toNot(equal(expected))

Values must be Equatable, Comparable, or subclasses of NSObject. equal will always fail when used to compare one or more nil values.

Identity

// Swift

// Passes if 'actual' has the same pointer address as 'expected':
expect(actual).to(beIdenticalTo(expected))
expect(actual) === expected

// Passes if 'actual' does not have the same pointer address as 'expected':
expect(actual).toNot(beIdenticalTo(expected))
expect(actual) !== expected

It is important to remember that beIdenticalTo only makes sense when comparing types with reference semantics, which have a notion of identity. In Swift, that means types that are defined as a class.

This matcher will not work when comparing types with value semantics such as those defined as a struct or enum. If you need to compare two value types, consider what it means for instances of your type to be identical. This may mean comparing individual properties or, if it makes sense to do so, conforming your type to Equatable and using Nimble's equivalence matchers instead.

// Objective-C

// Passes if 'actual' has the same pointer address as 'expected':
expect(actual).to(beIdenticalTo(expected));

// Passes if 'actual' does not have the same pointer address as 'expected':
expect(actual).toNot(beIdenticalTo(expected));

Comparisons

// Swift

expect(actual).to(beLessThan(expected))
expect(actual) < expected

expect(actual).to(beLessThanOrEqualTo(expected))
expect(actual) <= expected

expect(actual).to(beGreaterThan(expected))
expect(actual) > expected

expect(actual).to(beGreaterThanOrEqualTo(expected))
expect(actual) >= expected

// Objective-C

expect(actual).to(beLessThan(expected));
expect(actual).to(beLessThanOrEqualTo(expected));
expect(actual).to(beGreaterThan(expected));
expect(actual).to(beGreaterThanOrEqualTo(expected));

Values given to the comparison matchers above must implement Comparable.

Because of how computers represent floating point numbers, assertions that two floating point numbers be equal will sometimes fail. To express that two numbers should be close to one another within a certain margin of error, use beCloseTo:

// Swift

expect(actual).to(beCloseTo(expected, within: delta))

// Objective-C

expect(actual).to(beCloseTo(expected).within(delta));

For example, to assert that 10.01 is close to 10, you can write:

// Swift

expect(10.01).to(beCloseTo(10, within: 0.1))

// Objective-C

expect(@(10.01)).to(beCloseTo(@10).within(0.1));

There is also an operator shortcut available in Swift:

// Swift

expect(actual) ≈ expected
expect(actual) ≈ (expected, delta)

(Type option+x to get ≈ on a U.S. keyboard)

The former version uses the default delta of 0.0001. Here is yet another way to do this:

// Swift

expect(actual) ≈ expected ± delta
expect(actual) == expected ± delta

(Type option+shift+= to get ± on a U.S. keyboard)

If you are comparing arrays of floating point numbers, you'll find the following useful:

// Swift

expect([0.0, 2.0]) ≈ [0.0001, 2.0001]
expect([0.0, 2.0]).to(beCloseTo([0.1, 2.1], within: 0.1))

Values given to the beCloseTo matcher must conform to FloatingPoint.

Types/Classes

// Swift

// Passes if 'instance' is an instance of 'aClass':
expect(instance).to(beAnInstanceOf(aClass))

// Passes if 'instance' is an instance of 'aClass' or any of its subclasses:
expect(instance).to(beAKindOf(aClass))

// Objective-C

// Passes if 'instance' is an instance of 'aClass':
expect(instance).to(beAnInstanceOf(aClass));

// Passes if 'instance' is an instance of 'aClass' or any of its subclasses:
expect(instance).to(beAKindOf(aClass));

Instances must be Objective-C objects: subclasses of NSObject, or Swift objects bridged to Objective-C with the @objc prefix.

For example, to assert that dolphin is a kind of Mammal:

// Swift

expect(dolphin).to(beAKindOf(Mammal))

// Objective-C

expect(dolphin).to(beAKindOf([Mammal class]));

beAnInstanceOf uses the -[NSObject isMemberOfClass:] method to test membership. beAKindOf uses -[NSObject isKindOfClass:].

Truthiness

// Passes if 'actual' is not nil, true, or an object with a boolean value of true:
expect(actual).to(beTruthy())

// Passes if 'actual' is only true (not nil or an object conforming to Boolean true):
expect(actual).to(beTrue())

// Passes if 'actual' is nil, false, or an object with a boolean value of false:
expect(actual).to(beFalsy())

// Passes if 'actual' is only false (not nil or an object conforming to Boolean false):
expect(actual).to(beFalse())

// Passes if 'actual' is nil:
expect(actual).to(beNil())

// Objective-C

// Passes if 'actual' is not nil, true, or an object with a boolean value of true:
expect(actual).to(beTruthy());

// Passes if 'actual' is only true (not nil or an object conforming to Boolean true):
expect(actual).to(beTrue());

// Passes if 'actual' is nil, false, or an object with a boolean value of false:
expect(actual).to(beFalsy());

// Passes if 'actual' is only false (not nil or an object conforming to Boolean false):
expect(actual).to(beFalse());

// Passes if 'actual' is nil:
expect(actual).to(beNil());

Swift Assertions

If you're using Swift, you can use the throwAssertion matcher to check if an assertion is thrown (e.g. fatalError()). This is made possible by @mattgallagher's CwlPreconditionTesting library.

// Swift

// Passes if 'somethingThatThrows()' throws an assertion, 
// such as by calling 'fatalError()' or if a precondition fails:
expect { try somethingThatThrows() }.to(throwAssertion())
expect { () -> Void in fatalError() }.to(throwAssertion())
expect { precondition(false) }.to(throwAssertion())

// Passes if throwing an NSError is not equal to throwing an assertion:
expect { throw NSError(domain: "test", code: 0, userInfo: nil) }.toNot(throwAssertion())

// Passes if the code after the precondition check is not run:
var reachedPoint1 = false
var reachedPoint2 = false
expect {
    reachedPoint1 = true
    precondition(false, "condition message")
    reachedPoint2 = true
}.to(throwAssertion())

expect(reachedPoint1) == true
expect(reachedPoint2) == false

Notes:

• This feature is only available in Swift.
• The tvOS simulator is supported, but using a different mechanism, requiring you to turn off the Debug executable scheme setting for your tvOS scheme's Test configuration.

Swift Error Handling

You can use the throwError matcher to check if an error is thrown.

// Swift

// Passes if 'somethingThatThrows()' throws an 'Error':
expect { try somethingThatThrows() }.to(throwError())

// Passes if 'somethingThatThrows()' throws an error within a particular domain:
expect { try somethingThatThrows() }.to(throwError { (error: Error) in
    expect(error._domain).to(equal(NSCocoaErrorDomain))
})

// Passes if 'somethingThatThrows()' throws a particular error enum case:
expect { try somethingThatThrows() }.to(throwError(NSCocoaError.PropertyListReadCorruptError))

// Passes if 'somethingThatThrows()' throws an error of a particular type:
expect { try somethingThatThrows() }.to(throwError(errorType: NimbleError.self))

When working directly with Error values, using the matchError matcher allows you to perform certain checks on the error itself without having to explicitly cast the error.

The matchError matcher allows you to check whether or not the error:

• is the same type of error you are expecting.
• represents a particular error value that you are expecting.

This can be useful when using Result or Promise types, for example.

// Swift

let actual: Error = ...

// Passes if 'actual' represents any error value from the NimbleErrorEnum type:
expect(actual).to(matchError(NimbleErrorEnum.self))

// Passes if 'actual' represents the case 'timeout' from the NimbleErrorEnum type:
expect(actual).to(matchError(NimbleErrorEnum.timeout))

// Passes if 'actual' contains an NSError equal to the one provided:
expect(actual).to(matchError(NSError(domain: "err", code: 123, userInfo: nil)))

Note: This feature is only available in Swift.

Exceptions

// Swift

// Passes if 'actual', when evaluated, raises an exception:
expect(actual).to(raiseException())

// Passes if 'actual' raises an exception with the given name:
expect(actual).to(raiseException(named: name))

// Passes if 'actual' raises an exception with the given name and reason:
expect(actual).to(raiseException(named: name, reason: reason))

// Passes if 'actual' raises an exception which passes expectations defined in the given closure:
// (in this case, if the exception's name begins with "a r")
expect { exception.raise() }.to(raiseException { (exception: NSException) in
    expect(exception.name).to(beginWith("a r"))
})

// Objective-C

// Passes if 'actual', when evaluated, raises an exception:
expect(actual).to(raiseException())

// Passes if 'actual' raises an exception with the given name
expect(actual).to(raiseException().named(name))

// Passes if 'actual' raises an exception with the given name and reason:
expect(actual).to(raiseException().named(name).reason(reason))

// Passes if 'actual' raises an exception and it passes expectations defined in the given block:
// (in this case, if name begins with "a r")
expect(actual).to(raiseException().satisfyingBlock(^(NSException *exception) {
    expect(exception.name).to(beginWith(@"a r"));
}));

Note: Swift currently doesn't have exceptions (see #220). Only Objective-C code can raise exceptions that Nimble will catch.

Collection Membership

// Swift

// Passes if all of the expected values are members of 'actual':
expect(actual).to(contain(expected...))

// Passes if 'actual' is empty (i.e. it contains no elements):
expect(actual).to(beEmpty())

// Objective-C

// Passes if expected is a member of 'actual':
expect(actual).to(contain(expected));

// Passes if 'actual' is empty (i.e. it contains no elements):
expect(actual).to(beEmpty());

In Swift contain takes any number of arguments. The expectation passes if all of them are members of the collection. In Objective-C, contain only takes one argument for now.

For example, to assert that a list of sea creature names contains "dolphin" and "starfish":

// Swift

expect(["whale", "dolphin", "starfish"]).to(contain("dolphin", "starfish"))

// Objective-C

expect(@[@"whale", @"dolphin", @"starfish"]).to(contain(@"dolphin"));
expect(@[@"whale", @"dolphin", @"starfish"]).to(contain(@"starfish"));

contain and beEmpty expect collections to be instances of NSArray, NSSet, or a Swift collection composed of Equatable elements.

To test whether a set of elements is present at the beginning or end of an ordered collection, use beginWith and endWith:

// Swift

// Passes if the elements in expected appear at the beginning of 'actual':
expect(actual).to(beginWith(expected...))

// Passes if the the elements in expected come at the end of 'actual':
expect(actual).to(endWith(expected...))

// Objective-C

// Passes if the elements in expected appear at the beginning of 'actual':
expect(actual).to(beginWith(expected));

// Passes if the the elements in expected come at the end of 'actual':
expect(actual).to(endWith(expected));

beginWith and endWith expect collections to be instances of NSArray, or ordered Swift collections composed of Equatable elements.

Like contain, in Objective-C beginWith and endWith only support a single argument for now.

For code that returns collections of complex objects without a strict ordering, there is the containElementSatisfying matcher:

// Swift

struct Turtle {
    let color: String
}

let turtles: [Turtle] = functionThatReturnsSomeTurtlesInAnyOrder()

// This set of matchers passes regardless of whether the array is 
// [{color: "blue"}, {color: "green"}] or [{color: "green"}, {color: "blue"}]:

expect(turtles).to(containElementSatisfying({ turtle in
    return turtle.color == "green"
}))
expect(turtles).to(containElementSatisfying({ turtle in
    return turtle.color == "blue"
}, "that is a turtle with color 'blue'"))

// The second matcher will incorporate the provided string in the error message
// should it fail

// Objective-C

@interface Turtle : NSObject
@property (nonatomic, readonly, nonnull) NSString *color;
@end

@implementation Turtle 
@end

NSArray<Turtle *> * __nonnull turtles = functionThatReturnsSomeTurtlesInAnyOrder();

// This set of matchers passes regardless of whether the array is 
// [{color: "blue"}, {color: "green"}] or [{color: "green"}, {color: "blue"}]:

expect(turtles).to(containElementSatisfying(^BOOL(id __nonnull object) {
    return [[turtle color] isEqualToString:@"green"];
}));
expect(turtles).to(containElementSatisfying(^BOOL(id __nonnull object) {
    return [[turtle color] isEqualToString:@"blue"];
}));

For asserting on if the given Comparable value is inside of a Range, use the beWithin matcher.

// Swift

// Passes if 5 is within the range 1 through 10, inclusive
expect(5).to(beWithin(1...10))

// Passes if 5 is not within the range 2 through 4.
expect(5).toNot(beWithin(2..<5))

Strings

// Swift

// Passes if 'actual' contains 'substring':
expect(actual).to(contain(substring))

// Passes if 'actual' begins with 'prefix':
expect(actual).to(beginWith(prefix))

// Passes if 'actual' ends with 'suffix':
expect(actual).to(endWith(suffix))

// Passes if 'actual' represents the empty string, "":
expect(actual).to(beEmpty())

// Passes if 'actual' matches the regular expression defined in 'expected':
expect(actual).to(match(expected))

// Objective-C

// Passes if 'actual' contains 'substring':
expect(actual).to(contain(expected));

// Passes if 'actual' begins with 'prefix':
expect(actual).to(beginWith(prefix));

// Passes if 'actual' ends with 'suffix':
expect(actual).to(endWith(suffix));

// Passes if 'actual' represents the empty string, "":
expect(actual).to(beEmpty());

// Passes if 'actual' matches the regular expression defined in 'expected':
expect(actual).to(match(expected))

Collection Elements

Nimble provides a means to check that all elements of a collection pass a given expectation.

Swift

In Swift, the collection must be an instance of a type conforming to Sequence.

// Swift

// Providing a custom function:
expect([1, 2, 3, 4]).to(allPass { $0 < 5 })

// Composing the expectation with another matcher:
expect([1, 2, 3, 4]).to(allPass(beLessThan(5)))

Objective-C

In Objective-C, the collection must be an instance of a type which implements the NSFastEnumeration protocol, and whose elements are instances of a type which subclasses NSObject.

Additionally, unlike in Swift, there is no override to specify a custom matcher function.

// Objective-C

expect(@[@1, @2, @3, @4]).to(allPass(beLessThan(@5)));

Collection Count

// Swift

// Passes if 'actual' contains the 'expected' number of elements:
expect(actual).to(haveCount(expected))

// Passes if 'actual' does _not_ contain the 'expected' number of elements:
expect(actual).notTo(haveCount(expected))

// Objective-C

// Passes if 'actual' contains the 'expected' number of elements:
expect(actual).to(haveCount(expected))

// Passes if 'actual' does _not_ contain the 'expected' number of elements:
expect(actual).notTo(haveCount(expected))

For Swift, the actual value must be an instance of a type conforming to Collection. For example, instances of Array, Dictionary, or Set.

For Objective-C, the actual value must be one of the following classes, or their subclasses:

• NSArray,
• NSDictionary,
• NSSet, or
• NSHashTable.

Notifications

// Swift
let testNotification = Notification(name: Notification.Name("Foo"), object: nil)

// Passes if the closure in expect { ... } posts a notification to the default
// notification center.
expect {
    NotificationCenter.default.post(testNotification)
}.to(postNotifications(equal([testNotification])))

// Passes if the closure in expect { ... } posts a notification to a given
// notification center
let notificationCenter = NotificationCenter()
expect {
    notificationCenter.post(testNotification)
}.to(postNotifications(equal([testNotification]), from: notificationCenter))

// Passes if the closure in expect { ... } posts a notification with the provided names to a given
// notification center. Make sure to use this when running tests on Catalina, 
// using DistributedNotificationCenter as there is currently no way 
// of observing notifications without providing specific names.
let distributedNotificationCenter = DistributedNotificationCenter()
expect {
    distributedNotificationCenter.post(testNotification)
}.toEventually(postDistributedNotifications(equal([testNotification]),
                                  from: distributedNotificationCenter,
                                  names: [testNotification.name]))

This matcher is only available in Swift.

Result

// Swift
let aResult: Result<String, Error> = .success("Hooray") 

// passes if result is .success
expect(aResult).to(beSuccess()) 

// passes if result value is .success and validates Success value
expect(aResult).to(beSuccess { value in
    expect(value).to(equal("Hooray"))
})


enum AnError: Error {
    case somethingHappened
}
let otherResult: Result<String, AnError> = .failure(.somethingHappened) 

// passes if result is .failure
expect(otherResult).to(beFailure()) 

// passes if result value is .failure and validates error
expect(otherResult).to(beFailure { error in
    expect(error).to(matchError(AnError.somethingHappened))
}) 

This matcher is only available in Swift.

Matching a value to any of a group of matchers

// Swift

// passes if actual is either less than 10 or greater than 20
expect(actual).to(satisfyAnyOf(beLessThan(10), beGreaterThan(20)))

// can include any number of matchers -- the following will pass
// **be careful** -- too many matchers can be the sign of an unfocused test
expect(6).to(satisfyAnyOf(equal(2), equal(3), equal(4), equal(5), equal(6), equal(7)))

// in Swift you also have the option to use the || operator to achieve a similar function
expect(82).to(beLessThan(50) || beGreaterThan(80))

// Objective-C

// passes if actual is either less than 10 or greater than 20
expect(actual).to(satisfyAnyOf(beLessThan(@10), beGreaterThan(@20)))

// can include any number of matchers -- the following will pass
// **be careful** -- too many matchers can be the sign of an unfocused test
expect(@6).to(satisfyAnyOf(equal(@2), equal(@3), equal(@4), equal(@5), equal(@6), equal(@7)))

Note: This matcher allows you to chain any number of matchers together. This provides flexibility, but if you find yourself chaining many matchers together in one test, consider whether you could instead refactor that single test into multiple, more precisely focused tests for better coverage.

Custom Validation

// Swift

// passes if .succeeded is returned from the closure
expect {
    guard case .enumCaseWithAssociatedValueThatIDontCareAbout = actual else {
        return .failed(reason: "wrong enum case")
    }

    return .succeeded
}.to(succeed())

// passes if .failed is returned from the closure
expect {
    guard case .enumCaseWithAssociatedValueThatIDontCareAbout = actual else {
        return .failed(reason: "wrong enum case")
    }

    return .succeeded
}.notTo(succeed())

The String provided with .failed() is shown when the test fails.

When using toEventually() be careful not to make state changes or run process intensive code since this closure will be ran many times.

Writing Your Own Matchers

In Nimble, matchers are Swift functions that take an expected value and return a Predicate closure. Take equal, for example:

// Swift

public func equal<T: Equatable>(expectedValue: T?) -> Predicate<T> {
    // Can be shortened to:
    //   Predicate { actual in  ... }
    //
    // But shown with types here for clarity.
    return Predicate { (actualExpression: Expression<T>) throws -> PredicateResult in
        let msg = ExpectationMessage.expectedActualValueTo("equal <\(expectedValue)>")
        if let actualValue = try actualExpression.evaluate() {
            return PredicateResult(
                bool: actualValue == expectedValue!,
                message: msg
            )
        } else {
            return PredicateResult(
                status: .fail,
                message: msg.appendedBeNilHint()
            )
        }
    }
}

The return value of a Predicate closure is a PredicateResult that indicates whether the actual value matches the expectation and what error message to display on failure.

The actual equal matcher function does not match when expected are nil; the example above has been edited for brevity.

Since matchers are just Swift functions, you can define them anywhere: at the top of your test file, in a file shared by all of your tests, or in an Xcode project you distribute to others.

If you write a matcher you think everyone can use, consider adding it to Nimble's built-in set of matchers by sending a pull request! Or distribute it yourself via GitHub.

For examples of how to write your own matchers, just check out the Matchers directory to see how Nimble's built-in set of matchers are implemented. You can also check out the tips below.

PredicateResult

PredicateResult is the return struct that Predicate return to indicate success and failure. A PredicateResult is made up of two values: PredicateStatus and ExpectationMessage.

Instead of a boolean, PredicateStatus captures a trinary set of values:

// Swift

public enum PredicateStatus {
// The predicate "passes" with the given expression
// eg - expect(1).to(equal(1))
case matches

// The predicate "fails" with the given expression
// eg - expect(1).toNot(equal(1))
case doesNotMatch

// The predicate never "passes" with the given expression, even if negated
// eg - expect(nil as Int?).toNot(equal(1))
case fail

// ...
}

Meanwhile, ExpectationMessage provides messaging semantics for error reporting.

// Swift

public indirect enum ExpectationMessage {
// Emits standard error message:
// eg - "expected to <string>, got <actual>"
case expectedActualValueTo(/* message: */ String)

// Allows any free-form message
// eg - "<string>"
case fail(/* message: */ String)

// ...
}

Predicates should usually depend on either .expectedActualValueTo(..) or .fail(..) when reporting errors. Special cases can be used for the other enum cases.

Finally, if your Predicate utilizes other Predicates, you can utilize .appended(details:) and .appended(message:) methods to annotate an existing error with more details.

A common message to append is failing on nils. For that, .appendedBeNilHint() can be used.

Lazy Evaluation

actualExpression is a lazy, memoized closure around the value provided to the expect function. The expression can either be a closure or a value directly passed to expect(...). In order to determine whether that value matches, custom matchers should call actualExpression.evaluate():

// Swift

public func beNil<T>() -> Predicate<T> {
    // Predicate.simpleNilable(..) automatically generates ExpectationMessage for
    // us based on the string we provide to it. Also, the 'Nilable' postfix indicates
    // that this Predicate supports matching against nil actualExpressions, instead of
    // always resulting in a PredicateStatus.fail result -- which is true for
    // Predicate.simple(..)
    return Predicate.simpleNilable("be nil") { actualExpression in
        let actualValue = try actualExpression.evaluate()
        return PredicateStatus(bool: actualValue == nil)
    }
}

In the above example, actualExpression is not nil -- it is a closure that returns a value. The value it returns, which is accessed via the evaluate() method, may be nil. If that value is nil, the beNil matcher function returns true, indicating that the expectation passed.

Type Checking via Swift Generics

Using Swift's generics, matchers can constrain the type of the actual value passed to the expect function by modifying the return type.

For example, the following matcher, haveDescription, only accepts actual values that implement the Printable protocol. It checks their description against the one provided to the matcher function, and passes if they are the same:

// Swift

public func haveDescription(description: String) -> Predicate<Printable?> {
    return Predicate.simple("have description") { actual in
        return PredicateStatus(bool: actual.evaluate().description == description)
    }
}

Customizing Failure Messages

When using Predicate.simple(..) or Predicate.simpleNilable(..), Nimble outputs the following failure message when an expectation fails:

// where `message` is the first string argument and
// `actual` is the actual value received in `expect(..)`
"expected to \(message), got <\(actual)>"

You can customize this message by modifying the way you create a Predicate.

Basic Customization

For slightly more complex error messaging, receive the created failure message with Predicate.define(..):

// Swift

public func equal<T: Equatable>(_ expectedValue: T?) -> Predicate<T> {
    return Predicate.define("equal <\(stringify(expectedValue))>") { actualExpression, msg in
        let actualValue = try actualExpression.evaluate()
        let matches = actualValue == expectedValue && expectedValue != nil
        if expectedValue == nil || actualValue == nil {
            if expectedValue == nil && actualValue != nil {
                return PredicateResult(
                    status: .fail,
                    message: msg.appendedBeNilHint()
                )
            }
            return PredicateResult(status: .fail, message: msg)
        }
        return PredicateResult(bool: matches, message: msg)
    }
}

In the example above, msg is defined based on the string given to Predicate.define. The code looks akin to:

// Swift

let msg = ExpectationMessage.expectedActualValueTo("equal <\(stringify(expectedValue))>")

Full Customization

To fully customize the behavior of the Predicate, use the overload that expects a PredicateResult to be returned.

Along with PredicateResult, there are other ExpectationMessage enum values you can use:

public indirect enum ExpectationMessage {
// Emits standard error message:
// eg - "expected to <message>, got <actual>"
case expectedActualValueTo(/* message: */ String)

// Allows any free-form message
// eg - "<message>"
case fail(/* message: */ String)

// Emits standard error message with a custom actual value instead of the default.
// eg - "expected to <message>, got <actual>"
case expectedCustomValueTo(/* message: */ String, /* actual: */ String)

// Emits standard error message without mentioning the actual value
// eg - "expected to <message>"
case expectedTo(/* message: */ String)

// ...
}

For matchers that compose other matchers, there are a handful of helper functions to annotate messages.

appended(message: String) is used to append to the original failure message:

// produces "expected to be true, got <actual> (use beFalse() for inverse)"
// appended message do show up inline in Xcode.
.expectedActualValueTo("be true").appended(message: " (use beFalse() for inverse)")

For a more comprehensive message that spans multiple lines, use appended(details: String) instead:

// produces "expected to be true, got <actual>\n\nuse beFalse() for inverse\nor use beNil()"
// details do not show inline in Xcode, but do show up in test logs.
.expectedActualValueTo("be true").appended(details: "use beFalse() for inverse\nor use beNil()")

Supporting Objective-C

To use a custom matcher written in Swift from Objective-C, you'll have to extend the NMBPredicate class, adding a new class method for your custom matcher. The example below defines the class method +[NMBPredicate beNilMatcher]:

// Swift

extension NMBPredicate {
    @objc public class func beNilMatcher() -> NMBPredicate {
        return NMBPredicate { actualExpression in
            return try beNil().satisfies(actualExpression).toObjectiveC()
        }
    }
}

The above allows you to use the matcher from Objective-C:

// Objective-C

expect(actual).to([NMBPredicate beNilMatcher]());

To make the syntax easier to use, define a C function that calls the class method:

// Objective-C

FOUNDATION_EXPORT NMBPredicate *beNil() {
    return [NMBPredicate beNilMatcher];
}

Properly Handling nil in Objective-C Matchers

When supporting Objective-C, make sure you handle nil appropriately. Like Cedar, most matchers do not match with nil. This is to bring prevent test writers from being surprised by nil values where they did not expect them.

Nimble provides the beNil matcher function for test writer that want to make expectations on nil objects:

// Objective-C

expect(nil).to(equal(nil)); // fails
expect(nil).to(beNil());    // passes

If your matcher does not want to match with nil, you use Predicate.define or Predicate.simple. Using those factory methods will automatically generate expected value failure messages when they're nil.

public func beginWith<S: Sequence>(_ startingElement: S.Element) -> Predicate<S> where S.Element: Equatable {
    return Predicate.simple("begin with <\(startingElement)>") { actualExpression in
        guard let actualValue = try actualExpression.evaluate() else { return .fail }

        var actualGenerator = actualValue.makeIterator()
        return PredicateStatus(bool: actualGenerator.next() == startingElement)
    }
}

extension NMBPredicate {
    @objc public class func beginWithMatcher(_ expected: Any) -> NMBPredicate {
        return NMBPredicate { actualExpression in
            let actual = try actualExpression.evaluate()
            let expr = actualExpression.cast { $0 as? NMBOrderedCollection }
            return try beginWith(expected).satisfies(expr).toObjectiveC()
        }
    }
}

Migrating from the Old Matcher API

Previously (<7.0.0), Nimble supported matchers via the following types:

• Matcher
• NonNilMatcherFunc
• MatcherFunc

All of those types have been replaced by Predicate. The old API has been removed completely in Nimble v10.

Installing Nimble

Nimble can be used on its own, or in conjunction with its sister project, Quick. To install both Quick and Nimble, follow the installation instructions in the Quick Documentation.

Nimble can currently be installed in one of two ways: using CocoaPods, or with git submodules.

Installing Nimble as a Submodule

To use Nimble as a submodule to test your macOS, iOS or tvOS applications, follow these 4 easy steps:

1. Clone the Nimble repository
2. Add Nimble.xcodeproj to the Xcode workspace for your project
3. Link Nimble.framework to your test target
4. Start writing expectations!

For more detailed instructions on each of these steps, read How to Install Quick. Ignore the steps involving adding Quick to your project in order to install just Nimble.

Installing Nimble via CocoaPods

To use Nimble in CocoaPods to test your macOS, iOS or tvOS applications, add Nimble to your podfile and add the use_frameworks! line to enable Swift support for CocoaPods.

platform :ios, '8.0'

source 'https://github.com/CocoaPods/Specs.git'

# Whatever pods you need for your app go here

target 'YOUR_APP_NAME_HERE_Tests', :exclusive => true do
  use_frameworks!
  pod 'Nimble'
end

Finally run pod install.

Using Nimble without XCTest

Nimble is integrated with XCTest to allow it work well when used in Xcode test bundles, however it can also be used in a standalone app. After installing Nimble using one of the above methods, there are two additional steps required to make this work.

1. Create a custom assertion handler and assign an instance of it to the global NimbleAssertionHandler variable. For example:

class MyAssertionHandler : AssertionHandler {
    func assert(assertion: Bool, message: FailureMessage, location: SourceLocation) {
        if (!assertion) {
            print("Expectation failed: \(message.stringValue)")
        }
    }
}

// Somewhere before you use any assertions
NimbleAssertionHandler = MyAssertionHandler()

2. Add a post-build action to fix an issue with the Swift XCTest support library being unnecessarily copied into your app

• Edit your scheme in Xcode, and navigate to Build -> Post-actions
• Click the "+" icon and select "New Run Script Action"
• Open the "Provide build settings from" dropdown and select your target
• Enter the following script contents:

rm "${SWIFT_STDLIB_TOOL_DESTINATION_DIR}/libswiftXCTest.dylib"

You can now use Nimble assertions in your code and handle failures as you see fit.