{"id":33080,"date":"2021-07-08T12:06:33","date_gmt":"2021-07-08T16:06:33","guid":{"rendered":"https:\/\/mjtsai.com\/blog\/?p=33080"},"modified":"2021-07-08T12:06:33","modified_gmt":"2021-07-08T16:06:33","slug":"generic-test-classes-in-xcode-12-5","status":"publish","type":"post","link":"https:\/\/mjtsai.com\/blog\/2021\/07\/08\/generic-test-classes-in-xcode-12-5\/","title":{"rendered":"Generic Test Classes in Xcode 12.5"},"content":{"rendered":"

Jon Reid<\/a>:<\/p>\n

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Once or twice in my career, I’ve written an abstract test suite as a superclass, where the subclasses provide some sort of factory method. Then all the test cases in that suite get repeated for the specific instances.<\/p>\n<\/blockquote>\n\n

I do this all the time. It’s useful when I’m making a new, optimized version of a class and want to make sure it passes all the same tests as the original. And sometimes I need multiple implementations because certain APIs are broken on certain versions of the operating system.<\/p>\n\n

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Maybe you’ve wanted to repeat the same tests for a different object. For example, you may want to run the same test cases over different types that implement a protocol. Maybe you tried defining a generic XCTestCase<\/code>, hoping to reuse the test suite across a few types. If you tried this before, you know that it didn’t work. XCTest<\/code> uses introspection and follows specific rules to gather test cases and test suites. It didn’t pick up anything generic.<\/p>\n

But Xcode 12.5 adds support for generic test suites. Here’s how it works. Write a generic subclass of XCTestCase<\/code>.<\/p>\n

[…]<\/p>\n

And unlike the days when I did this with a quasi-abstract base class, XCTest<\/code> will not run any tests for the top-level generic suite.<\/p>\n<\/blockquote>\n\n

This is great. Also, note that in simpler cases his example with a factory method:<\/p>\n\n

\nclass AbstractSuite<T>: XCTestCase { … }\nclass OneClassTests: AbstractSuite<OneClass> {\n    override func makeSpecificObject() -> OneClass? {\n        \/* Make instance of OneClass*\/\n    }\n}\n<\/pre>\n
is more than you need. I often want to test a family of classes that all follow the same interface I<\/code>. Then you can just do:<\/p>\n
\nclass AbstractSuite<T: I>: XCTestCase { … }\nclass OneClassTests: AbstractSuite<OneClass> {}<\/pre>\n
and have the base class call T()<\/code> directly. The subclasses don’t need any code.<\/p>\n\n
Previously:<\/p>\n