You can find so many blogs from online and a lot of related answers from the StackOver, but I will check WWDC and Apple managed documentations first to understand the latest technology and the story behide the scene.
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Personally I just like the Playground with Xcode very much. It can save the time on coding and debugging, plus verifying any idea immediately.
Here is a video talking about Playground from WWDC 2018. Getting the most out of Playgrounds in Xcode (WWDC-2018)
And I played most of my code in Playground. The playground Repo on Github
Thanks to the XCTest, we don't have to write the test cases in the code directly and managed two versions of the source as I did before. I checked the WWDC and wrote an easy test cases for a function to resize the NSImage in playground.