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 iOS or OS X development, and is compatible with:
- OCUnit (SenTestingKit)
- Kiwi
- Cedar
- GHUnit
- Google Toolbox for Mac (GTM)
- OCMock
- OCMockito
Building:
If you want to build OCHamcrest yourself, clone the repo, then
$ git submodule update --init
$ cd Source
$ ./MakeDistribution.sh
If you have doxygen installed somewhere other than the Applications folder -- in /usr/local/bin, for example -- use this as the build step:
$ DOXYGEN=/usr/local/bin/doxygen ./MakeDistribution.sh
Or just use the pre-built release available at QualityCoding.org.
iOS Project Setup:
Add OCHamcrestIOS.framework to your project.
Add:
#define HC_SHORTHAND
#import <OCHamcrestIOS/OCHamcrestIOS.h>
OS X Project Setup:
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.
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
.
OCHamcrest comes with a library of useful matchers:
-
Object
conformsTo
- match object that conforms to protocolequalTo
- match equal objecthasDescription
- match object's-description
hasProperty
- match return value of method with given nameinstanceOf
- match object typeisA
- match object type precisely, no subclassesnilValue
,notNilValue
- matchnil
, or notnil
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 anint
) greaterThan
,greaterThanOrEqualTo
,lessThan
,lessThanOrEqualTo
- match numeric ordering
-
Text
containsString
- match part of a stringendsWith
- match the end of a stringequalToIgnoringCase
- match the complete string but ignore caseequalToIgnoringWhitespace
- match the complete string but ignore extra whitespacestartsWith
- match the beginning of a stringstringContainsInOrder
- match parts of a string, in relative order
-
Logical
allOf
- "and" together all matchersanyOf
- "or" together all matchersanything
- 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 collectioncontainsInAnyOrder
- match the entire collection, but in any orderempty
- match empty collectionhasCount
- match number of elements against another matcherhasCountOf
- match collection with given number of elementshasEntries
- match dictionary with list of key-value pairshasEntry
- match dictionary containing a key-value pairhasItem
- match if given item appears in the collectionhasItems
- match if all given items appear in the collection, in any orderhasKey
- match dictionary with a keyhasValue
- match dictionary with a valueonlyContains
- match if collection's items appear in given list
-
Decorator
describedAs
- give the matcher a custom failure descriptionis
- decorator to improve readability - seeSyntactic 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.
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
.
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. This commonly occurs when you find a fragment of code that tests the same set of properties over and over again (and in different tests), and you want to bundle the fragment into a single assertion. By writing your own matcher you'll eliminate code duplication and make your tests more readable!
Let's write our own matcher for testing if a calendar date falls on a Saturday. This is the test we want to write:
- (void)testDateIsOnASaturday
{
NSCalendarDate* date = [NSCalendarDate dateWithString:@"26 Apr 2008" calendarFormat:@"%d %b %Y"];
assertThat(date, is(onASaturday()))
}
Here's the interface:
#import <OCHamcrest/HCBaseMatcher.h>
#import <objc/objc-api.h>
@interface IsGivenDayOfWeek : HCBaseMatcher
{
NSInteger day; // Sunday is 0, Saturday is 6
}
+ (id)isGivenDayOfWeek:(NSInteger)dayOfWeek;
- (id)initWithDay:(NSInteger)dayOfWeek;
@end
OBJC_EXPORT id <HCMatcher> onASaturday();
The interface consists of two parts: a class definition, and a factory function (with C binding). Here's what the implementation looks like:
#import "IsGivenDayOfWeek.h"
#import <OCHamcrest/HCDescription.h>
@implementation IsGivenDayOfWeek
+ (id)isGivenDayOfWeek:(NSInteger)dayOfWeek
{
return [[self alloc] initWithDay:dayOfWeek];
}
- (id)initWithDay:(NSInteger)dayOfWeek
{
self = [super init];
if (self)
day = dayOfWeek;
return self;
}
// Test whether item matches.
- (BOOL)matches:(id)item
{
if (![item respondsToSelector:@selector(dayOfWeek)])
return NO;
return [item dayOfWeek] == day;
}
// Describe the matcher.
- (void)describeTo:(id <HCDescription>)description
{
NSString* dayAsString[] =
{ @"Sunday", @"Monday", @"Tuesday", @"Wednesday", @"Thursday", @"Friday", @"Saturday" };
[[description appendText:@"calendar date falling on "] appendText:dayAsString[day]];
}
@end
id <HCMatcher> onASaturday()
{
return [IsGivenDayOfWeek isGivenDayOfWeek:6];
}
For our Matcher implementation we implement the -matches:
method (which
calls -dayOfWeek
after confirming that the argument has such a method) and
the -describe_to:
method (which is used to produce a failure message when a
test fails). Here's an example of how the failure message looks:
NSCalendarDate* date = [NSCalendarDate dateWithString: @"6 April 2008" calendarFormat: @"%d %B %Y"];
assertThat(date, is(onASaturday()));
fails with the message
Expected: is calendar date falling on Saturday, got: <06 April 2008>
and Xcode shows it as a build error. Clicking the error message takes you to the assertion that failed.
Even though the onASaturday
function creates a new matcher each time it is
called, you should not assume this is the only usage pattern for your matcher.
Therefore you should make sure your matcher is stateless, so a single instance
can be reused between matches.
- Documentation
- Sources
- Hamcrest
- Quality Coding - Tools, tips & techniques for building quality in to iOS development