I am new in OCMock.
I use dispatch_once() created a singleton class MyManager :
#implementation MyManager
+ (id)sharedInstance {
static MyManager *sharedMyManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedMyManager = [[self alloc] init];
});
return sharedMyManager;
}
I have a method in School class which uses the above singleton:
#implementation School
...
- (void) createLecture {
MyManager *mgr = [MyManager sharedInstance];
[mgr checkLectures];
...
}
#end
Now, I want to unit test this method, I use a partial mock of MyManager:
- (void) testCreateLecture {
// create a partially mocked instance of MyManager
id partialMockMgr = [OCMockObject partialMockForObject:[MyManager sharedInstance]];
// run method to test
[schoolToTest createLecture];
...
}
I noticed that with OCMock, after I created the partial mock of my singleton MyManager instance, when run my method under test, it automatically use the partially mocked instance.
This is a bit weird to me, since in my test case above, I only created the partial mock of MyManager instance without injecting it to MyManager class,
how does OCMock automatically force the code under test use this mocked instance when [MyManager sharedInstance] is called in the code under test ? Could someone explain to me this?
partialMockForObject mocks the object you are passing to it.
In this case you are mocking the singleton (shared) object. You don't have to inject anything because sharedInstance is always returning the same object, now mocked. It is still the same reference.
Imagine partial mocking as a simple mutation of the passed object, it doesn't create a new instance so you don't have to inject it in this specific case.
Partial Mocks are pretty cool. Behind the scenes, OCMock subclasses the class you are mocking, and any method that you stub is updated in the partial mock subclass. So all references to your mocked class will now default to the subclass (mocked implementation) instead of the superclass (your implementation). There's a good explanation in the reference on this as well.
Related
I am using OCMock 3 to unit test my iOS project.
I use dispatch_once() created a singleton class MyManager :
#implementation MyManager
+ (id)sharedInstance {
static MyManager *sharedMyManager = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
sharedMyManager = [[self alloc] init];
});
return sharedMyManager;
}
I have a method in School class which uses the above singleton:
#implementation School
...
- (void) createLecture {
MyManager *mgr = [MyManager sharedInstance];
[mgr checkLectures];
...
}
#end
Now, I want to unit test this method, I use a partial mock of MyManager:
- (void) testCreateLecture {
// create a partially mocked instance of MyManager
id partialMockMgr = [OCMockObject partialMockForObject:[MyManager sharedInstance]];
// run method to test
[schoolToTest createLecture];
...
}
- (void)tearDown {
// I want to set the singleton instance to nil, how to?
[super tearDown];
}
In tearDown phase, I want to set the singleton instance to nil so that the following test case could start from clean state.
I know on internet, some people suggest to move the static MyManager *sharedMyManager outside the +(id)sharedInstance method. But I would like to ask, is there any way to set the instance to nil without moving it outside +(id)sharedInstance method? (Any solution like java reflection?)
You can't achieve what you want with a local static variable. Block-scoped statics are only visible inside their lexical context.
We do this by making the singleton instance a static variable scoped to the class implementation and adding a mutator to override it. Generally that mutator is only called by tests.
#implementation MyManager
static MyManager *_sharedInstance = nil;
static dispatch_once_t once_token = 0;
+(instancetype)sharedInstance {
dispatch_once(&once_token, ^{
if (_sharedInstance == nil) {
_sharedInstance = [[MyManager alloc] init];
}
});
return _sharedInstance;
}
+(void)setSharedInstance:(MyManager *)instance {
once_token = 0; // resets the once_token so dispatch_once will run again
_sharedInstance = instance;
}
#end
Then in your unit test:
// we can replace it with a mock object
id mockManager = [OCMockObject mockForClass:[MyManager class]];
[MyManager setSharedInstance:mockManager];
// we can reset it so that it returns the actual MyManager
[MyManager setSharedInstance:nil];
This also works with partial mocks, as in your example:
id mockMyManager = [OCMockObject partialMockForObject:[MyManager sharedInstance]];
[[mockMyManager expect] checkLectures];
[MyManager setSharedInstance:mockMyManager];
[schoolToTest createLecture];
[mockMyManager verify];
[mockMyManager stopMocking];
// reset it so that it returns the actual MyManager
[MyManager setSharedInstance:nil];
Here's a full breakdown of the approach.
The answer is no, because you use dispatch_once(&onceToken, ^{ so even if you added another method which could reset the variable to nil you'd never be able to initialise it again.
So you already have one solution and the best solution is to not access the singleton directly (use dependency injection instead).
It is an easier way to solute your issue.
Your class have a singleton. you can add a method that is destroy this class instance. So when you call shareManager method again , it will create a new instance.
Such as:
static MyManager *sharedMyManager = nil;
+ (void)destroy
{
sharedMyManager = nil;
}
As others have stated, what you should really do is refactor your code to use dependency injection. This means that if the School class needs a MyManager instance to operate, then it should have an initWithManager:(MyManager *)manager method which should be the designated initializer. Or if the MyManager is only needed in this particular method, it should be a method parameter, e.g. createLectureWithManager:(MyManager *)manager.
Then in your tests, you could just do School *schoolToTest = [[School alloc] initWithManager:[[MyManager alloc] init]], and each test would have a new MyManager instance. You could drop the singleton pattern entirely, removing the sharedInstance method on MyManager and your application's logic would be responsible to ensure that there is only one instance that you pass around.
But sometimes, you have to work with legacy code that you can't just refactor. In these cases, you need to stub the class method. That is, you need to replace the implementation of -[MyManager sharedInstance] with an implementation that returns [[MyManager alloc] init]. This can be accomplished using the runtime to swizzle the class method, which would be the equivalent of Java reflection that you are looking for. See this for an example of how to use the runtime.
You can also do it with OCMock, which uses the runtime behind the scenes, just like mocking frameworks in Java are based on the reflection API :
MyManager *testManager = [[MyManager alloc] init];
id mock = [[OCMockObject mockForClass:[MyManager class]];
[[[mock stub] andReturn:testManager] sharedInstance];
If you don't want to refactor your code for easier unit testing then there is another solution (not perfect but works):
Create a local property of MyManager type
In setUp instantiate the property from above and swizzle the sharedInstance method with your local method (e.g. swizzle_sharedInstance)
Inside the swizzle_sharedInstance return the local property
In tearDown swizzle back to original sharedInstance and nullify the local property
I suggest a little bit different approach. You can create a mock of your sharedInstance using OCMock:
id myManagerMock = OCMClassMock([MyManager class]);
OCMStub([myManagerMock sharedManager]).andReturn(myManagerMock);
Now School implementation will use myManagerMock object, and you can stub this object to return anything you want under you test case. For example:
OCMStub([myManagerMock someMethodThatReturnsBoolean]).andReturn(YES);
It's important that after your tests, you will perform cleaning of your mock object by calling (at the end of your test method or in -tearDown):
[myManagerMock stopMocking];
I have couple of classes that should be inherited from some A class.
Each of them should be a Singleton.
Can this be achieved?
This realization of Singleton-pattern allows the inheritance:
+ (instancetype)sharedInstance {
static dispatch_once_t once;
static NSMutableDictionary *sharedInstances;
dispatch_once(&once, ^{ /* This code fires only once */
// Creating of the container for shared instances for different classes
sharedInstances = [NSMutableDictionary new];
});
id sharedInstance;
#synchronized(self) { /* Critical section for Singleton-behavior */
// Getting of the shared instance for exact class
sharedInstance = sharedInstances[NSStringFromClass(self)];
if (!sharedInstance) {
// Creating of the shared instance if it's not created yet
sharedInstance = [self new];
sharedInstances[NSStringFromClass(self)] = sharedInstance;
}
}
return sharedInstance;
}
You never, ever inherit from a Singleton class. That completely breaks the concept of a Singleton in a bad way.
Having multiple singleton classes inheriting from the same base class: No problem whatsoever. In fact, most singletons have the common superclass NSObject, but you can use any other superclass.
Yes. I'm not sure if you're familiar with Obj-C singleton patterns, but here is a guide:
http://www.galloway.me.uk/tutorials/singleton-classes/
There shouldn't be any more complications in subclassing. Just create a subclass of the singleton, and it will inherit it's singleton abilities as well. I think each subclass will create it's own unique singleton, but if not, override the singleton generator so it's unique for that subclass.
Keep in mind, singletons are falling out of favor on iOS, so they should be used sparingly. I try to only use them when attempting to create multiple instances is simply not possible (i.e. a class for accessing a hardware resource that must be reserved exclusively by a class.)
I havea Utility class that uses class methods. I am trying to refer to self in the class method but can't. I was wondering how would I declare the following in a class method:
[MRProgressOverlayView showOverlayAddedTo:self.window animated:YES];
self.window it says member reference type struct objc_class *' is a pointer; maybe you meant to use '->'
Another problem that relates to not being able to call self is how would I refer to a declared #property in my .h in a class method in my .m.
Here is my class method:
.m
+ (void)showHUD
{
[UIApplication sharedApplication].networkActivityIndicatorVisible=YES;
[MRProgressOverlayView showOverlayAddedTo:self.window animated:YES];
//I would preferably like to call my property here instead
}
.h
#property (nonatomic) MRProgress * mrProgress;
The whole point of a class method is that it is not part of a specific instance. Inside of a class method, self is the class.
If you need to be tied to a specific instance, then it should be an instance method. If you want a static method that accesses a specific instance, then pass that instance (self) to it (though it's hard to imagine many cases where that makes sense).
In the above example, showHUD should be an instance method almost certainly. If that doesn't make sense for some reason, then it should be:
+ (void)showHUDForWindow:(UIWindow *)window;
You can then call it as showHUDForWindow:self.window and use that as needed.
You can use a singleton pattern. Singleton pattern assumes that the only instance of your class exists. Since it's the only instance, you can then use it from class methods.
Example implementation:
+ (MyClass*)sharedInstance {
static dispatch_once_t once;
static MyClass *sharedMyClass;
dispatch_once(&once, ^ {
sharedMyClass = [[self alloc] init];
});
return sharedMyClass;
}
Then you can access the shared instance via [MyClass sharedInstance], for example:
+ (void)doSomethingCool {
[[self sharedMyClass] doSomething];
}
I have a class where I keep utility methods; one of those methods takes the values in some textboxes stored in a ViewController and saves those values to a plist.
The problem is the utility methods class is not a ViewController and therefore I can't "hook up" the outlet properties of the textboxes tothe Utility class.
Is there a way I can pass the ViewController as a parameter to the Utility class method?
Just make the utilities class a Singleton inheriting just from NSObject. That way you can easily access the methods wherever you'd like and you'll only have one instance of it.
https://developer.apple.com/library/ios/documentation/general/conceptual/DevPedia-CocoaCore/Singleton.html
Matt Gallagher wrote a great helper file to create Singletons. Check it out here:
http://www.cocoawithlove.com/2008/11/singletons-appdelegates-and-top-level.html
If these utility methodes are class methods use a singleton. Something like this:
+ (__CMMotionManager__ *)__sharedMotionManager__ {
static __CMMotionManager__ *shared = nil;
if (!shared) {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{ // all threads will block here until the block executes
shared = [[__CMMotionManager__ alloc] init]; // this line of code can only ever happen once
});
}
return shared;
}
(it's my CoreMotionManager snippet)
I am learning OCMock for iOS testing. What's the difference between "class mock" and "partial mock", and when should you use one vs the other?
http://ocmock.org/features/
Class mocks create objects that are pure mocks of a class instance.
Partial mocks take an instance of a class an allow you to stub any of its methods.
Suppose I have these classes:
#interface Foo : NSObject
- (void)doX;
#end
#implementation
- (void)doX
{
NSLog(#"X");
}
#end
#interface Bar : NSObject
- (void)doA:(Foo *)foo;
- (void)doB;
#end
#implementation Bar
- (void)doA:(Foo *)foo
{
NSLog(#"A");
[foo doX];
[self doB];
}
- (void)doB
{
NSLog(#"B");
}
#end
I'm interested in testing Bar's doA: method. I expect it to call doX on a Foo object, then to call its own doB method. I would implement this using a class mock of a Foo and a partial mock of a Bar.
- (void)test_doA_shouldCall_doX_and_doB
{
id objectUnderTest = [OCMockObject partialMockForObject:[Bar new]];
id fooMock = [OCMockObject mockForClass:Foo.class];
[[fooMock expect] doX];
[[objectUnderTest expect] doB];
// Make the call
[objectUnderTest doA:fooMock];
[objectUnderTest verify];
[fooMock verify];
}
You see here that my partial mock allowed me to call the real method I wanted to test while mocking an internal call to another of its instance methods. Because I didn't need any of the real functionality of Foo, however, I used a class mock.