OCHamcrest

Contents:

• What is OCHamcrest?
• How do I add OCHamcrest to my project?
• My first OCHamcrest test
• Predefined matchers
• Syntactic sugar
• Writing custom matchers
• More resources

What is OCHamcrest?

OCHamcrest is:

• a library of "matcher" objects that let you declare rules for whether a given object matches the criteria or not.
• 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.

OCHamcrest is used for both Mac and iOS development with:

• OCUnit (SenTestingKit) built in to Xcode
• Google Toolbox for Mac (GTM)
• GHUnit
• Cedar BDD framework
• OCMock
• OCHandMock
• OCMockito

How do I add OCHamcrest to my project?

Rather than build OCHamcrest yourself, I recommend you use the pre-built release available in Downloads. This works for projects using Automatic Reference Counting (ARC) as well as for projects using traditional memory management.

(But if you still want to build OCHamcrest yourself, go into the Source folder and execute MakeDistribution.sh from Terminal.)

The steps vary slightly depending on whether your project is a Mac project or an iOS project:

Mac:

• Add OCHamcrest.framework to your project.
• Add a Copy Files build phase to copy OCHamcrest.framework to your Products Directory. For unit test bundles, make sure this Copy Files phase comes before the Run Script phase that executes tests.
• Add

  #define HC_SHORTHAND
  #import <OCHamcrest/OCHamcrest.h>
  

Note: If your Console shows

otest[57510:203] *** NSTask: Task create for path '...' failed: 22, "Invalid argument".  Terminating temporary process.

double-check your Copy Files phase.

iOS:

• Add OCHamcrestIOS.framework to your project.
• Add "-lstdc++" and "-ObjC" to your "Other Linker Flags".
• Add

  #define HC_SHORTHAND
  #import <OCHamcrestIOS/OCHamcrestIOS.h>
  

My first OCHamcrest test

We'll start by writing a very simple Xcode unit test, but instead of using OCUnit's STAssertEqualObjects function, we'll use OCHamcrest's assertThat construct and a predefined matcher:

#import <SenTestingKit/SenTestingKit.h>

#define HC_SHORTHAND
#import <OCHamcrest/OCHamcrest.h>

@interface BiscuitTest : SenTestCase
@end

@implementation BiscuitTest

- (void)testEquals
{
    Biscuit* theBiscuit = [Biscuit biscuitNamed:@"Ginger"];
    Biscuit* myBiscuit = [Biscuit biscuitNamed:@"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, shorthand macros are provided if HC_SHORTHAND is defined before including the OCHamcrest header. For example, instead of writing HC_assertThat, simply write assertThat.

Predefined matchers

OCHamcrest comes with a library of useful matchers:

• Object
  • equalTo - match equal object
  • hasDescription - match object's -description
  • hasProperty - match return value of method with given name
  • instanceOf - match object type
  • conformsToProtocol - match object protocol conformance
  • nilValue, notNilValue - match for nil, or not nil
  • sameInstance - match same object
• Number
  • closeTo - match number close to a given value
  • equalTo<TypeName> - match number equal to a primitive number (such as equalToInt for an int)
  • greaterThan, greaterThanOrEqualTo, lessThan, lessThanOrEqualTo - match numeric ordering
• Text
  • containsString - 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 - match parts of a string, in relative order
• Logical
  • allOf - "and" together all matchers
  • anyOf - "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 - exactly match the entire collection
  • containsInAnyOrder - match the entire collection, but in any order
  • empty - match empty collection
  • hasCount - match number of elements against another matcher
  • hasCountOf - match collection with given number of elements
  • hasEntries - match dictionary with list of key-value pairs
  • hasEntry - match dictionary containing a key-value pair
  • hasItem - match if given item appears in the collection
  • hasItems - match if all given items appears in the collection, in any order
  • hasKey - match dictionary with a key
  • hasValue - match dictionary with a value
  • onlyContains - match if collections'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));

Writing custom matchers

A key feature of OCHamcrest is its extensibility. See Writing custom matchers for an example of how to write your own matchers.

More resources

• OCHamcrest documentation
• Latest OCHamcrest sources
• Official Hamcrest website PyHamcrest - Python version.
• Quality Coding - Tools, tips & techniques for building quality in to iOS development.