running the lib2to3 tests from an installed location, I see the following failures on the 3.7 branch:

======================================================================
FAIL: test (lib2to3.tests.test_fixers.Test_reload)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 294, in test
    self.check(b, a)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 36, in check
    tree = self._check(before, after)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 32, in _check
    self.assertEqual(after, str(tree))
AssertionError: 'import importlib\nimportlib.reload(a)\n\n' != 'import imp\nimp.reload(a)\n\n'
- import importlib
?           ------
+ import imp
- importlib.reload(a)
?    ------
+ imp.reload(a)
  


======================================================================
FAIL: test_comment (lib2to3.tests.test_fixers.Test_reload)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 299, in test_comment
    self.check(b, a)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 36, in check
    tree = self._check(before, after)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 32, in _check
    self.assertEqual(after, str(tree))
AssertionError: 'import importlib\nimportlib.reload( a ) # comment\n\n' != 'import imp\nimp.reload( a ) # comment\n\n'
- import importlib
?           ------
+ import imp
- importlib.reload( a ) # comment
?    ------
+ imp.reload( a ) # comment
  


======================================================================
FAIL: test_space (lib2to3.tests.test_fixers.Test_reload)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 309, in test_space
    self.check(b, a)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 36, in check
    tree = self._check(before, after)
  File "/usr/lib/python3.7/lib2to3/tests/test_fixers.py", line 32, in _check
    self.assertEqual(after, str(tree))
AssertionError: 'import importlib\nimportlib.reload( a )\n\n' != 'import imp\nimp.reload( a )\n\n'
- import importlib
?           ------
+ import imp
- importlib.reload( a )
?    ------
+ imp.reload( a )
  


----------------------------------------------------------------------
Ran 650 tests in 27.363s

FAILED (failures=3)
test test_lib2to3 failed
1 test failed again:
    test_lib2to3

== Tests result: FAILURE then FAILURE ==

390 tests OK.

1 test failed:
    test_lib2to3

Could be related to https://bugs.python.org/issue21446 .

I'm not able to reproduce this:

 ./configure
 make -s -j
 sudo make install
 python3.7 -m test test_lib2to3

 Run tests sequentially
 0:00:00 load avg: 0.86 [1/1] test_lib2to3

 == Tests result: SUCCESS ==

 1 test OK.

 Total duration: 13 sec 456 ms
 Tests result: SUCCESS

strange. I see it succeeding in the build location, not the install location.  Did you make sure to cd /tmp before running the test?

I still can reproduce it:

$ python3.7 -m test test_lib2to3
Run tests sequentially
0:00:00 load avg: 0.24 [1/1] test_lib2to3
test test_lib2to3 failed -- multiple errors occurred; run in verbose mode for details
test_lib2to3 failed

== Tests result: FAILURE ==

1 test failed:
    test_lib2to3

Total duration: 5 sec 211 ms
Tests result: FAILURE

I ran "python3.7 -m test test_lib2to3" in a separate terminal. I don't remember the exact location, but I'm sure it wasn't the build location (it was probably my home directory)

Is it possible to add some debug print()s inside https://github.com/python/cpython/blob/3.7/Lib/lib2to3/tests/support.py#L37 ? My only guess is that the test code somehow finds the wrong refactorer.

test_lib2to3 passes for me on Win 10 for both installed 3.7.0 (in home directory) and repository 3.7 (in clone directory) compiled yesterday.

I can't reproduce this either using a current top of 3.7 branch and installed on macOS; I also tried building 3.7 just prior to the fix for Issue21446 that Brett mentioned; the test also did not fail.  Let's close this until it can be reproduced outside of doko's environment.