问在OCUnit中使用核心数据类时出现Apple Mach-O链接器错误

EN

 - (NSManagedObjectContext*)managedObjectContextWithConcurrencyType:(NSManagedObjectContextConcurrencyType)concurrencyType {
    NSManagedObjectModel *mom = [NSManagedObjectModel mergedModelFromBundles:nil];
    STAssertNotNil(mom, @"Can not create MOM from main bundle");

    NSPersistentStoreCoordinator *psc = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:mom];
    STAssertNotNil(psc, @"Can not create persistent store coordinator");
    NSPersistentStore *store = [psc addPersistentStoreWithType:NSInMemoryStoreType configuration:nil URL:nil options:nil error:0];
    STAssertNotNil(store, @"Can not create In-Memory persistent store");

    NSManagedObjectContext *moc = [[NSManagedObjectContext alloc] initWithConcurrencyType:concurrencyType];
    moc.persistentStoreCoordinator = psc;

    return moc;
}

Undefined symbols for architecture i386:
  "_NSInMemoryStoreType", referenced from:
      -[CrosswordItemTests managedObjectContextWithConcurrencyType:] in CrosswordItemTests.o
  "_OBJC_CLASS_$_NSEntityDescription", referenced from:
      objc-class-ref in CrosswordItemTests.o
      "_OBJC_CLASS_$_NSManagedObjectContext", referenced from:
      objc-class-ref in CrosswordItemTests.o
  "_OBJC_CLASS_$_NSManagedObjectModel", referenced from:
      objc-class-ref in CrosswordItemTests.o
  "_OBJC_CLASS_$_NSPersistentStoreCoordinator", referenced from:
      objc-class-ref in CrosswordItemTests.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

#import <CoreData/CoreData.h>