Writing FIRST Swift Tests

Be a FIRST-class Developer!

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Photo by Nina Mercado on Unsplash

Prerequisites:

  • None, although the real example given below is quite in depth

Terminology

Unit test: Software testing where individual units or components of the software is Software testing where individual units or components of the software is tests

Why test?

Testing your classes is really important, giving confidence in your code and allowing programmers to both maintain your code (Good) and proof that your code meets the contract of what it should do.

When changes are made to code during development, breaking changes proves that code needs to be looked at again until all of the tests pass.

This is Test Driven Development, but having FIRST tests actually goes further than that.

What are FIRST tests?

  • Fast

so let us dive in and see what each of these mean in turn:

Fast Tests need to be quick, in such a such a way that developers won’t be discouraged from using them. Developers won’t run all the tests regularly if they take too long to run, and then what is the point in having them?

Independent Tests should be independent of the state of the previous test. If you have a database that deletes a record, the next test shouldn’t fail because that particular record is missing! In Swift we have the option of using override func setUpWithError() throws which runs at the beginning of each test to do any necessary prep work.

Repeatable Repeatable means that tests do not depend on the environment that they belong in. If a test fails it is because the code that is running on that test fails, not a dependency and because another test is running at a similar time. The tests should always run with the expected output,

Self-validating We are helped out with the way that the iOS SDK sets up tests for us, in that they either pass or fail. There should be no need for someone running the tests to understand how they are set up or how they run — either they pass or they don’t.

Timely Tests shouldn’t be left until the end of a sprint, any production cycle or even when you have finished (in your opinion) your code. They should be written as and when they are useful to be run. Some will see this as an interpretation of Test Driven Development, but it doesn’t have to be. You should be writing tests to prove that your code is of sufficient quality for the job that it is performing.

Example

Watch the following video for my SQLiteManager shows how this can be added into a genuine project.

Essentially, if you are using a database you could choose to have a version in your production and test target and test target (in this case I have production.sqlite and testDB.sqlite)

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This is fine, but within tests we would not have a **repeatable** set of tests — because if you make any change in the `test.db` (like deleting a record) — so the following test:

makes the following test unreliable (because no matter the order of the tests in Xcode, we cannot guarentee the order that the test run) -

So the right method of approaching this problem is to use a wrapper for Sqlite3 functions, and invoking the power of Dependency Injection in Swift.

The mock looks something like the following:

Which of course conforms to a protocol Sqlite3WrapperProtocol as shown here:

You can then call the concrete object with something like the following:

which is repeatable, since we are never actually deleting the records from a database. I bit more effort, true, but in effect we are able to create tests that actually test our code that can be run in a reasonable time and are repeatable.

If you’ve got some specific questions about this, you can certainly get in touch with me on Twitter

Conclusion

Please do join the fun bus: Testing! Respect what it tries to achieve and please start to implement it at your workplace in your projects. They will be better as a result!

As you move through your career this becomes more so — you never want to ship code that is anything less than excellent! In order to help you on your way, you might like to know about TDD, ATDD and BDD as well as the theoretical testing of iOS apps and Injection testing.

If you’ve any questions, comments or suggestions please hit me up on Twitter

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