Using OCMock to mock [[UIDevice currentDevice] userInterfaceIdiom]

Question

I am learning to use OCMocks with my unit tests and I understand the basics. However, I'm not sure how I could mock calls to class methods.

I'd like to have:

[[UIDevice currentDevice] userInterfaceIdiom]

return different (but valid) interface idioms for my test cases.

id mock = [OCMockObject mockForClass:[UIDevice class]];

// Would I use a mock or a stub to have UIDevice mock return
// currentDevice and then from it, return userInterfaceIdiom

Answer 1

Mocking singletons is tricky. You can do it with some runtime magic. It's possible to do with the help of Matt Gallagher's invokeSupersequent macro . Basically, you add a category to your test case that overrides currentDevice to return a mock, only if you've set the mock. Here's the setup:

#import "NSObject+SupersequentImplementation.h"

#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wobjc-protocol-method-implementation"

@implementation UIDevice (UnitTests)

+(id)currentDevice {
    if ([BaseTestCase mockDevice]) {
        return [BaseTestCase mockDevice];
    }

    return invokeSupersequentNoArgs();
}

@end

#pragma clang diagnostic pop


static id mockDevice = nil;

+(id)mockDevice {
    return mockDevice;
}

+(id)createMockDevice {
    mockDevice = [OCMockObject mockForClass:[UIDevice class]];
    return mockDevice;
}

+(id)createNiceMockDevice {
    mockDevice = [OCMockObject niceMockForClass:[UIDevice class]];
    return mockDevice;
}

-(void)tearDown {
    mockDevice = nil;
    [super tearDown];
}

Then, in your test:

-(void)testShouldDoSomethingOnIpad {
    id mockDevice = [BaseTestCase createNiceMockDevice];
    [[[mockDevice stub] andReturnValue:OCMOCK_VALUE(UIUserInterfaceIdiomPad)] userInterfaceIdiom];

    // do something iPad-specific

    [mockDevice verify];
}

I did a more detailed write-up of this approach a while back.

Answer 2

Here's a simple solution:

OCMockObject* _deviceMock = OCMPartialMock([UIDevice currentDevice]);

[[[_deviceMock stub] andReturnValue:@(UIUserInterfaceIdiomPad)] userInterfaceIdiom];

Just make sure the code in your behavior uses this check

[UIDevice currentDevice].userInterfaceIdiom

INSTEAD of the macro

UI_USER_INTERFACE_IDIOM()

Answer 3

An alternate approach is to put both variants in your tests, and run the tests in the iPhone and iPad simulators. Admittedly, this is a bit of a hassle.

-(void)testShouldDoSomething {
    if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
        // test iPad behavior
    } else {
        // test iPhone behavior
    }
}