A 'support' sub-module in unittest is ok. I wonder if it is the best name?

- is_jython

This is too specific and ignores the other implementations. This information is also available from sys / platform modules. 

-1

- TESTFN

This is a global for setting the directory temporary files are created in? Don't think I like the global approach. Which functions is it used by?

- forget

This is the equivalent of sys.modules.pop(module_name, None) but it also deletes bytecode. I don't think a bytecode deleting API is needed in unittest.

-1


- findfile

I need to look at the code, don't understand it from the description in the docs.

- check_warnings

Could be useful.

- captured_stdout

Could be useful.

- TransientResource

I need to look at how it is used, but sounds useful.

- transient_internet

Not documented, I need to look at the code / how it is used.

- EnvironmentVarGuard

Could be useful.

- WarningsRecorder

Used by catch_warnings I guess.

- cpython_only

Not documented but could be useful.

- temp_cwd

Not documented but could be useful.

- sortdict

Not documented but could be useful.