OCMockito is an Objective-C implementation of Mockito, supporting creation, verification and stubbing of mock objects.

Key differences from other mocking frameworks:

• Mock objects are always "nice," recording their calls instead of throwing exceptions about unspecified invocations. This makes tests less fragile.

• No expect-run-verify, making tests more readable. Mock objects record their calls, then you verify the methods you want.

• Verification failures are reported as unit test failures, identifying specific lines instead of throwing exceptions. This makes it easier to identify failures. (It also keeps the pre-iOS 5 Simulator from crashing.)

Adding OCMockito to your project

Building:

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

$ git submodule update --init
$ cd Source
$ ./MakeDistribution.sh

Or just use the pre-built release available at QualityCoding.org.

iOS Project Setup:

Add both OCHamcrestIOS.framework and OCMockitoIOS.framework to your project.

Add:

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

#define MOCKITO_SHORTHAND
#import <OCMockitoIOS/OCMockitoIOS.h>

OS X Project Setup:

Add both OCHamcrest.framework and OCMockito.framework and to your project.

Add a Copy Files build phase to copy both OCHamcrest.framework and OCMockito.framework and 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>

#define MOCKITO_SHORTHAND
#import <OCMockito/OCMockito.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.

Let's verify some behavior!

// mock creation
NSMutableArray *mockArray = mock([NSMutableArray class]);

// using mock object
[mockArray addObject:@"one"];
[mockArray removeAllObjects];

// verification
[verify(mockArray) addObject:@"one"];
[verify(mockArray) removeAllObjects];

Once created, the mock will remember all interactions. Then you can selectively verify whatever interactions you are interested in.

(If Xcode complains about multiple methods with the same name, cast verify to the mocked class.)

How about some stubbing?

// mock creation
NSArray *mockArray = mock([NSArray class]);

// stubbing
[given([mockArray objectAtIndex:0]) willReturn:@"first"];

// following prints "(null)" because objectAtIndex:999 was not stubbed
NSLog(@"%@", [mockArray objectAtIndex:999]);

How do you mock a class object?

Class mockStringClass = mockClass([NSString class]);

How do you mock a protocol?

id <MyDelegate> delegate = mockProtocol(@protocol(MyDelegate));

How do you mock an object that also implements a protocol?

UIViewController <CustomProtocol> *controller =
    mockObjectAndProtocol([UIViewController class], @protocol(CustomProtocol));

How do you stub methods that return non-objects?

To stub methods that return non-object types, specify willReturn<type>, like this:

[given([mockArray count]) willReturnUnsignedInteger:3];

Argument matchers

OCMockito verifies argument values by testing for equality. But when extra flexibility is required, you can specify OCHamcrest matchers.

// mock creation
NSMutableArray *mockArray = mock([NSMutableArray class]);

// using mock object
[mockArray removeObject:@"This is a test"];

// verification
[verify(mockArray) removeObject:startsWith(@"This is")];

OCHamcrest matchers can be specified as arguments for both verification and stubbing.

Typed arguments will issue a warning that the matcher is the wrong type. Just cast the matcher to id.

How do you specify matchers for primitive arguments?

To stub a method that takes a primitive argument but specify a matcher, invoke the method with a dummy argument, then call -withMatcher:forArgument:

[[given([mockArray objectAtIndex:0]) withMatcher:anything() forArgument:0]
 willReturn:@"foo"];

Use the shortcut -withMatcher: to specify a matcher for a single argument:

[[given([mockArray objectAtIndex:0]) withMatcher:anything()]
 willReturn:@"foo"];

Verifying exact number of invocations / at least x / never

// using mock
[mockArray addObject:@"once"];

[mockArray addObject:@"twice"];
[mockArray addObject:@"twice"];

// the following two verifications work exactly the same
[verify(mockArray) addObject:@"once"];
[verifyCount(mockArray, times(1)) addObject:@"once"];

// verify exact number of invocations
[verifyCount(mockArray, times(2)) addObject:@"twice"];
[verifyCount(mockArray, times(3)) addObject:@"three times"];

// verify using never(), which is an alias for times(0)
[verifyCount(mockArray, never()) addObject:@"never happened"];

// verify using atLeast
[verifyCount(mockArray, atLeastOnce()) addObject:@"at least once"];
[verifyCount(mockArray, atLeast(2)) addObject:@"at least twice"];

More resources

• Sources
• OCHamcrest
• Quality Coding - Tools, tips & techniques for building quality in to iOS development.