Testsuite can fail to execute in parallel

The way the testsuite is designed currently prevents its safe execution in parallel. During my last run, I got the following error log:

22/86 Test #25: export_file.py ..................................   Passed    0.50 sec
      Start 27: file_source.py
      Start 28: freeze_property_modifier.py
      Start 29: global_namespace.py
      Start 30: histogram_modifier.py
23/86 Test #26: export_file_text.py .............................***Failed    0.81 sec
ERROR: The Python script 'export_file_text.py' has exited with an error.
Traceback (most recent call last):
  File "export_file_text.py", line 10, in <module>
    os.remove("test.data")
FileNotFoundError: [Errno 2] No such file or directory: 'test.data'

After inspection of the code, both export_file.py and export_file_ext.py unconditionally try to remove a bunch of test files, including test.data which one can remove for the other. There are multiple ways to solve this, I'd say the simplest would be to use different names for files generated and eventually cleaned by each test.