$ ./python -m test -v -m test_from_tuple test_decimal
...
test_from_tuple (test.test_decimal.CWhitebox) ... FAIL

======================================================================
FAIL: test_from_tuple (test.test_decimal.CWhitebox)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/serhiy/py/cpython/Lib/test/test_decimal.py", line 5413, in test_from_tuple
    self.assertEqual(str(c.create_decimal(x)), '-0E-1000026')
AssertionError: '-0E-1000007' != '-0E-1000026'
- -0E-1000007
?          ^^
+ -0E-1000026
?          ^^


----------------------------------------------------------------------

I think the tests are order-dependent in multiple places.  Personally, I don't see much value in fixing that because it has little effect on the actual code.

Doesn't this mean that the test is incorrect? It expects the result be '-0E-1000026', but actually it should be '-0E-1000007', and it is '-0E-1000026' only after performing some actions outside of the test. Or maybe that there is a leak of the state out of localcontext?

The test is insignificant. The real tests are mpdecimal-testit- 2.4.1.tar.gz (http://www.bytereef.org/mpdecimal/download.html), deccheck.py and my private python test suite.

This test uses the global context that has been modified somewhere. I think I added that test to increase code coverage.

The thread local context was modified in test_round(), so prec=28 was used in test_from_tuple() when running the whole test suite but prec=9 when running the single test.

I don't really consider that a bug, but it is easy to "fix".

I wouldn't be surprised if other similar cases exist.

I ran all tests separately and this was the only case. PR 7355 fixes it. There are no other failures, errors or warnings.

    ./python -m test -uall --list-cases test_decimal | xargs -n1 -I '{}' ./python -We -m test -vuall -m '{}' test_decimal

New changeset e95dfc5006d19e59c7871faa9973356844ddb3ae by Stefan Krah in branch 'master':
bpo-33750: Reset thread-local context precision in test_round(). (#7355)
https://github.com/python/cpython/commit/e95dfc5006d19e59c7871faa9973356844ddb3ae

New changeset 7f1bcda9bc3c04100cb047373732db0eba00e581 by Stefan Krah (Miss Islington (bot)) in branch '3.6':
bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) (#7356)
https://github.com/python/cpython/commit/7f1bcda9bc3c04100cb047373732db0eba00e581

New changeset bdab3ea8b98db2133ef1e2d92b2a2c539f08ddaf by Stefan Krah (Miss Islington (bot)) in branch '3.7':
bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) (#7357)
https://github.com/python/cpython/commit/bdab3ea8b98db2133ef1e2d92b2a2c539f08ddaf

OK, thanks for checking the other tests!