What is OCHamcrest?

OCHamcrest is an Objective-C library providing:

• a library of “matcher” objects for declaring rules to check whether a given object matches those rules.
• a framework for writing your own matchers.

Matchers are useful for a variety of purposes, such as UI validation. But they're most commonly used for writing unit tests that are expressive and flexible.

My first OCHamcrest test

We‘ll start by writing a very simple Xcode unit test, but instead of using XCTest’s XCTAssertEqualObjects function, we‘ll use OCHamcrest’s assertThat construct and a predefined matcher:

#import <XCTest/XCTest.h>
#import <OCHamcrest/OCHamcrest.h>

@interface BiscuitTest : XCTestCase
@end

@implementation BiscuitTest

- (void)testEquals
{
    Biscuit* theBiscuit = [[Biscuit alloc] initWithName:@"Ginger"];
    Biscuit* myBiscuit = [[Biscuit alloc] initWithName:@"Ginger"];
    assertThat(theBiscuit, equalTo(myBiscuit));
}

@end

The assertThat function is a stylized sentence for making a test assertion. In this example, the subject of the assertion is the object theBiscuit, which is the first method parameter. The second method parameter is a matcher for Biscuit objects, here a matcher that checks one object is equal to another using the -isEqual: method. The test passes since the Biscuit class defines an -isEqual: method.

OCHamcrest's functions are actually declared with an “HC_” package prefix (such as HC_assertThat and HC_equalTo) to avoid name clashes. To make test writing faster and test code more legible, optional short syntax is provided by default. For example, instead of writing HC_assertThat, simply write assertThat.

Predefined matchers

OCHamcrest comes with a library of useful matchers:

• Object

  • conformsTo - match object that conforms to protocol
  • equalTo - match equal object
  • hasDescription - match object's -description
  • hasProperty - match return value of method with given name
  • instanceOf - match object type
  • isA - match object type precisely, no subclasses
  • nilValue, notNilValue - match nil, or not nil
  • sameInstance - match same object
  • throwsException - match block that throws an exception
  • HCArgumentCaptor - match anything, capturing all values

• Number

  • closeTo - match number close to a given value
  • greaterThan, greaterThanOrEqualTo, lessThan, lessThanOrEqualTo - match numeric ordering
  • isFalse - match zero
  • isTrue - match non-zero

• Text

  • containsSubstring - match part of a string
  • endsWith - match the end of a string
  • equalToIgnoringCase - match the complete string but ignore case
  • equalToIgnoringWhitespace - match the complete string but ignore extra whitespace
  • startsWith - match the beginning of a string
  • stringContainsInOrder, stringContainsInOrderIn - match parts of a string, in relative order

• Logical

  • allOf, allOfIn - “and” together all matchers
  • anyOf, anyOfIn - “or” together all matchers
  • anything - match anything (useful in composite matchers when you don't care about a particular value)
  • isNot - negate the matcher

• Collection

  • contains, containsIn - exactly match the entire collection
  • containsInAnyOrder, containsInAnyOrderIn - match the entire collection, but in any order
  • containsInRelativeOrder, containsInRelativeOrderIn - match collection containing items in relative order
  • everyItem - match if every item in a collection satisfies a given matcher
  • hasCount - match number of elements against another matcher
  • hasCountOf - match collection with given number of elements
  • hasEntries - match dictionary with key-value pairs in a dictionary
  • hasEntriesIn - match dictionary with key-value pairs in a list
  • hasEntry - match dictionary containing a key-value pair
  • hasItem - match if given item appears in the collection
  • hasItems, hasItemsIn - match if all given items appear in the collection, in any order
  • hasKey - match dictionary with a key
  • hasValue - match dictionary with a value
  • isEmpty - match empty collection
  • isIn - match when object is in given collection
  • onlyContains, onlyContainsIn - match if collection's items appear in given list

• Decorator

  • describedAs - give the matcher a custom failure description
  • is - decorator to improve readability - see “Syntactic sugar” below

The arguments for many of these matchers accept not just a matching value, but another matcher, so matchers can be composed for greater flexibility. For example, only_contains(endsWith(@".")) will match any collection where every item is a string ending with period.

Syntactic sugar

OCHamcrest strives to make your tests as readable as possible. For example, the is matcher is a wrapper that doesn't add any extra behavior to the underlying matcher. The following assertions are all equivalent:

assertThat(theBiscuit, equalTo(myBiscuit));
assertThat(theBiscuit, is(equalTo(myBiscuit)));
assertThat(theBiscuit, is(myBiscuit));

The last form is allowed since is wraps non-matcher arguments with equalTo. Other matchers that take matchers as arguments provide similar shortcuts, wrapping non-matcher arguments in equalTo.

How can I assert on an asynchronous call?

assertWithTimeout will keep evaluating an expression until the matcher is satisfied or a timeout is reached. For example,

assertWithTimeout(5, thatEventually(self.someString), is(@"expected"));

This repeatedly checks for this string to evaluate to “expected” before timing out after 5 seconds. thatEventually is a convenience macro to create a block.

Writing custom matchers

OCHamcrest comes bundled with lots of useful matchers, but you'll probably find that you need to create your own from time to time to fit your testing needs. See the “Writing Custom Matchers” guide for more information.

What about Swift?

Try the native Swift implementation of Hamcrest.

How do I add OCHamcrest to my project?

The Examples folder shows projects using OCHamcrest either through CocoaPods or through the prebuilt frameworks, for iOS and Mac OS X development.

CocoaPods

If you want to add OCHamcrest using Cocoapods then add the following dependency to your Podfile. Most people will want OCHamcrest in their test targets, and not include any pods from their main targets:

target 'MyTests' do
  inherit! :search_paths
  pod 'OCHamcrest', '~> 6.0'
end

Use the following import:

#import <OCHamcrest/OCHamcrest.h>

Carthage

Add the following to your Cartfile:

github "hamcrest/OCHamcrest" ~> 6.0

Then drag the the built framework from the appropriate Carthage/Build directory into your project, but with “Copy items into destination group's folder” disabled.

Prebuilt Frameworks

Prebuilt binaries are available on GitHub. The binaries are packaged as frameworks:

• OCHamcrestIOS.framework for iOS development
• OCHamcrest.framework for Mac OS X development

Drag the appropriate framework into your project, specifying “Copy items into destination group's folder”. Then specify -ObjC in your “Other Linker Flags”.

iOS Development:

Use the following import:

#import <OCHamcrestIOS/OCHamcrestIOS.h>

Mac OS X Development:

Add a “Copy Files” build phase to copy OCHamcrest.framework to your Products Directory.

Use the following import:

#import <OCHamcrest/OCHamcrest.h>

Build Your Own

If you want to build OCHamcrest yourself, clone the repo, then

$ cd Source
$ ./MakeDistribution.sh