I would like to know if there is any way to tell Xcode to run unit tests in a specified order. I mean not in a same XCTestCase class file, but between all the class file.
The OP did not mention whether CI is available or whether a command line answer would be sufficient. In those cases, I have enjoyed using xctool [1]. It has syntax to run tests down to just a single test method:
path/to/xctool.sh \
-workspace YourWorkspace.xcworkspace \
-scheme YourScheme \
test -only SomeTestTarget:SomeTestClass/testSomeMethod
I will do this to ensure we test the items we think are easiest first.
1.[] facebook/xctool: A replacement for Apple's xcodebuild that makes it easier to build and test iOS or OSX apps. ; ; https://github.com/facebook/xctool