Why should I use a separate test target for running XCTests and how should I do that?

Question

I once asked a question related to XCTests. And in one of the answers I was told that it is a common practice to use a separate test target (other than the main app) when running unit tests (at least, in iOS development). I tried to find some sources about it, but I couldn't

I understand, that it is probably a best practice, so I would really like to understand it. Could someone explain to me why is it important, what benefits do I get from it and how should I go about doing it? Links to some articles explaining the issue will be much appreciated.

P.S. I understand that I need special environment for tests (fake in-memory database, mocked networking layer, etc.), but up until now I managed to achieve it without a separate test host. But I believe that there might be a better way.

Answer 1

To answer your points:

1. Why is using a separate test target important?

Separation of concerns. A unit test target does not have the same kind of structure as a regular app target - it contains a test bundle, which references the app target under test, as well as the test classes and any helper classes required. It is not a duplicate of the app target with test code added to it - in fact it should not even contain the code under test. This means that you don't have to make any special effort to keep the test target in sync with the main app target - the fact that the test bundle loads the main app handles all that for you. (You made a comment on Richard Ross's answer to your previous q suggesting you've run into the difficulties duplication causes already).

2. How should I go about doing this? (checked on Xcode 7).

Assuming you are wanting to add a target to an existing project that doesn't have any tests, select the main project, and then click on the '+' beneath the list of targets in the project. You can also use the File->New->Target menu option. You'll see a menu asking you to choose a template for your new target. Select 'Test' and within test select 'iOS Unit Testing Bundle'. Check the fields in the next screen - they should be correct by default - but you might want to double check the 'Target to be Tested' field value is correct if you have a lot of targets in the project/workspace. Click 'OK' and you should have a functioning unit test bundle, with an example test that you should be able to run using Apple-U or Product->Test You'll still need to #import the app classes if you're using ObjC.

If you are creating a new project, all you need to do is tick the 'Include Unit Test' box when creating the project - no other steps are required.

• Apple Docs (with links to relevant WWDC presentations)

• Tutorials. Most of the tutorials around are a bit out of date. But not that much has changed, so just look at the docs and figure it out. The two below might be useful, otherwise just google. From a quick glance, most of them seem to assume that the project had unit tests set up at the beginning

http://www.raywenderlich.com/22590/beginning-automated-testing-with-xcode-part-12 (2012/iOS 6, but the process is still broadly the same. Also deals with Jenkins, Git and running tests from the CLI).

Unit testing in OSX - most recent post - not iOS, I know, but more up to date than most of the iOS tutorials (Oct 2015), and gives step by step instructions (including setting the unit test target in the build schemes, which probably won't be necessary in your case). Probably worth a look anyway.