---
title: "TDD-ing your Realm objects in Xcode Playgrounds"
url: "https://www.pardel.dev/2017/04/05/tdd-ing-your-realm-objects-in-xcode-playgrounds"
date: 2017-04-05
author: "Paul Ardeleanu"
tags: ["Swift","iOS","TDD"]
description: "Learn how to test Realm object and truly embrace test driven development in Xcode Playgrounds - with Realm Mobile Database."
---

# TDD-ing your Realm objects in Xcode Playgrounds

In 2 previous posts, I've shown [how to do Test-Driven Development (TDD)](/2017/03/27/tdd-in-xcode-playgrounds) and [how to use 3rd party frameworks in Xcode Playgrounds](/2018/10/10/3rd-party-frameworks-in-xcode-playgrounds). This blog post ties them together so you'll need to read those 2 posts first to make sense of this one.

If you've never used [Realm Mobile Database](https://realm.io/?ref=pardel.dev) before, head over to [Realm Swift documentation pages](https://docs.mongodb.com/realm-legacy/docs/swift/latest/?ref=pardel.dev). In short, it is a fast, open-source alternative to SQLite and CoreData — allows you to store your data fast in a cross-platform format. There is also a [Realm Browser app](https://apps.apple.com/gb/app/realm-browser/id1007457278?mt=12&ref=pardel.dev) that can be downloaded from the Mac App Store.


## The Task object and TestCase

![The Task object and TestCase](/assets/images/blog/2017-04-05-tdd-ing-your-realm-objects-in-xcode-playgrounds/image_1.png "The Task object and TestCase")

Let's go through this one step at a time.

### Import PlaygroundWrapper and RealmSwift

As mentioned in [Using 3rd party frameworks in Xcode Playgrounds](/2018/10/10/3rd-party-frameworks-in-xcode-playgrounds), this technique allows us to bring Realm support into the playgrounds.


### Task realm object

I've created a simple Realm object with one property — Realm objects must have at least one property. In my case this an uuid that gets a randomly generated string when created.

```swift
class Task: Object {
    dynamic var uuid = UUID().uuidString
}
```

### TaskTests

As described in [TDD in Xcode Playgrounds](/2017/03/27/tdd-in-xcode-playgrounds), I've created a subclass of `XCTestCase` and run a test suite.

The class also contains 2 properties that will help with the testing.

```swift
class TaskTests: XCTestCase {
    var realm: Realm!
    var task: Task!
    
    ...
    
}

TaskTests.defaultTestSuite().run()
```

### The setup

The “magic” here is the use of in memory Realm databases with a random identifier. This ensures that a new fresh realm is created before each test.

Setting the `Realm.Configuration.defaultConfiguration` allows us to not having to store the configuration for later use — we can simply address the realm as `Realm()`.

```swift
override func setUp() {
    super.setUp()
    Realm.Configuration.defaultConfiguration = 
        Realm.Configuration(inMemoryIdentifier: UUID().uuidString)

    task = Task()
    realm = try! Realm()
    try! realm.write {
        realm.add([task])
    }
}
```


### The test: `testSetup()`

Fairly straigtforward — we're testing that we have one and only one realm objects of type `Task`.

```swift
func testSetup() {
    let tasks = try! Realm().objects(Task.self)
    XCTAssertEqual(tasks.count, 1)
}
```

From here onwards, the world is your oyster...

The project can be found on github: [https://github.com/pardel/tdd-realm-playgrounds](https://github.com/pardel/tdd-realm-playgrounds).


### But is it fast?

Oh yes, it's fast: https://realm.io/news/introducing-realm/#fast - Realm was designed and built for performance.

Last but not least, imagine TDD-ing with Core Data, Playgrounds or not. 🤓