Create in memory NSManagedObjectContext for testing classes that use CoreData.

DMMTestUtilities.h

//
//  DMMTestUtilities.h
//  dmiedema
//
//  Created by Daniel on 8/25/14.
//  Copyright (c) 2014 Daniel Miedema. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface DMMTestUtilities : NSObject
/*!
 Create and return an in memory @c NSManagedObjectContext for testing
 
 Each call will return a new @c NSManagedObjectContext. Call with caution.
 
 @return NSManagedObjectContext with an @c NSInMemoryStoreType for testing
 */
+ (NSManagedObjectContext *)inMemoryManagedObjectContext;
@end

DMMTestUtilities.m

//
//  DMMTestUtilities.m
//  dmiedema
//
//  Created by Daniel on 8/25/14.
//  Copyright (c) 2014 Daniel Miedema. All rights reserved.
//

#import "DMMTestUtilities.h"

@interface DMMTestUtilities()
@property (strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@end

@implementation DMMTestUtilities
+ (NSManagedObjectContext *)inMemoryManagedObjectContext {
    DMMTestUtilities *testHelper = [[DMMTestUtilities alloc] init];
    
    NSURL *url = [[NSBundle mainBundle] URLForResource:@"sqlite" withExtension:@"momd"];
    testHelper.managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:url];
    testHelper.persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:testHelper.managedObjectModel];
    
    if (![testHelper.persistentStoreCoordinator addPersistentStoreWithType:NSInMemoryStoreType configuration:nil URL:nil options:nil error:nil]) {
        return nil;
    }
    
    testHelper.managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    testHelper.managedObjectContext.persistentStoreCoordinator = testHelper.persistentStoreCoordinator;
    
    return testHelper.managedObjectContext;
}

@end