How can I reset Realm's state between tests?

Question

We've been using RLMClearRealmCache to clear Realm's state between tests that are testing migrations. If the cache is not cleared, the next test will not perform migrations, since the cache still reports the schema being up to date, even though we've deleted and replaced realm fixture file (which has an old schema).

RLMClearRealmCache was moved to an Objective-C++ file recently, so we want to stop using it and avoid using Objective-C++ in our project. Is this still the best/only way of doing it?

To be clear, we are not using in-memory Realm for these specs. We have a default.realm fixture file we've saved from a device at a specific release and we're doing the following to use it:

- (void)loadBundledRealmWithName:(NSString *)name;
{
    [self deleteOnDiskRealm];

    // copy over the file to the location
    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *documentsDirectory = [paths objectAtIndex:0];
    NSString *source = [[NSBundle bundleForClass:[self class]] pathForResource:name ofType:@"realm"];
    if (documentsDirectory && source) {
        NSString *destination = [documentsDirectory stringByAppendingPathComponent:kDefaultRealmFileName];
        [[NSFileManager defaultManager] copyItemAtPath:source toPath:destination error:nil];
    }
}

However, between test cases, without a call to RLMClearRealmCache, it seems as though Realm's cache determines that migrations have already been run, even though we've swapped out the .realm file and they need to be run again.

joern · Answer 1 · 2016-03-01T06:50:58.587

2

You can use a separate in-memory Realm for each test. When you do that each test gets a "fresh" Realm and the Realm's state does not leak from one test to another.

To achieve that all you have to to is set the Realm's Configuration inMemoryIdentifer to the name of the current test before running it. You can do that in your XCTestCase subclass setUp method (as suggested in the Realm Documentation):

override func setUp() {
    super.setUp()
    Realm.Configuration.defaultConfiguration.inMemoryIdentifier = self.name
}

EDIT:

This answer does not fit the updated question but I'll leave it here anyway because it might help others searching for a way to reset Realm's state between tests.

edited Mar 01 '16 at 06:50

answered Feb 27 '16 at 22:52

joern

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I should have been more clear that we aren't using in-memory Realm. I've updated my question. – solidcell Feb 29 '16 at 18:45
Ah, ok. Should I delete this answer or should we leave it in case it helps someone else who searches for "reset Realm state between tests"? – joern Feb 29 '16 at 19:28
Yea, I think leaving it could only help others. – solidcell Feb 29 '16 at 23:14

score 0 · Accepted Answer · answered Mar 01 '16 at 23:51

We ended up getting Realm to clear its cache by leveraging the fact that it will do so if it is no longer referenced. It was just a bit tricky to track down the issue stopping it from doing so: we were retaining a reference to a Realm object between test runs:

context(@"some context", ^{
    __block MyRealmObject *whoops;

    beforeEach(^{
        [specHelper loadBundledRealmWithName:@"release-50-fixture.realm"];
        [migrationManager performMigrations];
        whoops = [[MyRealmObject allObjects] firstObject];
    });

    it(@"first", ^{
        // migrations will run for this `it`
    });

    it(@"second", ^{
        // migrations will NOT run for this `it` since the old Realm is still around and its cache thinks migrations have already run (even though we've swapped out the backing DB).
        // the issue is that `whoops` is retaining a `MyRealmObject` and thus the Realm.
    });
});

How can I reset Realm's state between tests?

2 Answers2