Reading file names from a file looks misleading.

$ ls Lib/ctypes/test/*.py > list
$ head list
Lib/ctypes/test/__init__.py
Lib/ctypes/test/__main__.py
Lib/ctypes/test/test_anon.py
Lib/ctypes/test/test_array_in_pointer.py
Lib/ctypes/test/test_arrays.py
Lib/ctypes/test/test_as_parameter.py
Lib/ctypes/test/test_bitfields.py
Lib/ctypes/test/test_buffers.py
Lib/ctypes/test/test_bytes.py
Lib/ctypes/test/test_byteswap.py
$ ./python -m test --fromfile=list 
Run tests sequentially
0:00:00 [ 1/51] test_anon
test test_anon crashed -- Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/libregrtest/runtest.py", line 152, in runtest_inner
    the_module = importlib.import_module(abstest)
  File "/home/serhiy/py/cpython/Lib/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 978, in _gcd_import
  File "<frozen importlib._bootstrap>", line 961, in _find_and_load
  File "<frozen importlib._bootstrap>", line 948, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'test.test_anon'
...

I wouldn't add this feature unless support full file names.