Refer to https://groups.google.com/g/testng-users/c/KpPqUAzEVSw

This small project indicates an issue with testng running in parallel=classes mode, yet executing different classes in the same thread but out of order. The problem occurs when:

1) Using 1 thread.
2) One class is a static inner class of another.
3) We select the class (or the folder) to create the eclipse launch file.

The problem does not occur when:

1) We run the tests on the project using the testng.xml file.
2) The static inner class to moved to its own file.

Included is a ISuiteListener that sets parallel=classes. However, this does not change the issue.

Executing tests by running the issue src folder in the eclipse environment. Tests run out of order.

Executing tests by running testng.xml in the eclipse environment. Everything works correctly.