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Wrap up

This has been the longest technique project by a long way, but I think you've learned a lot about the importance of good unit testing. We also managed to cover some functional programming techniques, discussed private setters, used functions as parameters, and even tried NSCountedSet, so I hope you're happy with the result!

Now that the full suite of tests are complete, you have three options ahead of you. First, you can run all the tests in a file by clicking the diamond (or green checkmark) next to the name of the test class. So, in Project39UITests.swift look in the gutter next to class Project39UITests: XCTestCase and click that. Second, you can run all the tests in your entire project by pressing Cmd+U. Give it a few moments to run, then you'll get a complete report.

Third, and most impressively, you can run all your tests on Xcode Server, which is the beginning of continuous integration: every time you commit a code change to source control, Xcode Server can pull down those changes, build the app, and run the full suite of tests. If you're working in a team, Xcode can produce a visual display of tests that are passing and failing, which is either motivational or depressing depending on your workplace!

If you'd like to take this app further, you should concentrate on testing. Can you write a test that verifies there are 55 table rows when the user filters by words that appear 1000 or more times? Can you write a test that ensures something sensible happens if the cancel button is pressed? Can you write a performance test to ensure applyUserFilter() doesn't get any slower?

There's also a bug in the code that you ought to be able to fix easily: if the user enters nothing into the filter text box, applyUserFilter() gets called with an empty string as its parameter and no results will be shown. It's down to you to think up a better solution: is it better to pretend Cancel was tapped instead? Or perhaps consider an empty string to mean "show all words"? It's your project now, so please choose what you think best.

Keep in mind that testing is only part of a sensible code review process. Yes, Xcode Server can check out your code and automatically validate that tests pass, but it is not a substitute for actual human interaction – looking through each other's code, and providing constructive criticism. Taking the time to read someone else's code, then encouraging and supporting them as they improve it, is a key developer skill – remember, code review is where mistakes get rubbed out, not rubbed in.

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About the author

Paul Hudson is the creator of Hacking with Swift, the most comprehensive series of Swift books in the world. He's also the editor of Swift Developer News, the maintainer of the Swift Knowledge Base, and Mario Kart world champion. OK, so that last part isn't true. If you're curious you can learn more here.

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