I want to know how to enable the area with red.
I found this post: Use Xcode's Test Classes Assistant Editor with Swift Classes
A file with a base name of FooTest or FooTests is now considered a counterpart of a file with a base name of Foo for navigation and the Assistant Editor. (28981734)
I tried, one file named Formula.swift, the other on in Test Projects named FormulaTests.swift, but not worked, do not show in assistant editor auto.
How to enable Test Classes/Called in Assistant Editor of Xcode quickly? Left is source code, right is unit test, that is what I want.