Failed separate test_from_tuple in test_decimal

[serhiy-storchaka]

BPO	33750
Nosy	@rhettinger, @facundobatista, @mdickinson, @skrah, @serhiy-storchaka
PRs	bpo-33750: Reset thread-local context precision in test_round(). #7355 [3.6] bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) #7356 [3.7] bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) #7357

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2018-06-03.17:39:06.167>
created_at = <Date 2018-06-03.12:44:18.956>
labels = ['3.7', '3.8', 'type-bug', 'tests']
title = 'Failed separate test_from_tuple in test_decimal'
updated_at = <Date 2018-06-03.17:39:06.166>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2018-06-03.17:39:06.166>
actor = 'skrah'
assignee = 'none'
closed = True
closed_date = <Date 2018-06-03.17:39:06.167>
closer = 'skrah'
components = ['Tests']
creation = <Date 2018-06-03.12:44:18.956>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 33750
keywords = ['patch']
message_count = 10.0
messages = ['318542', '318546', '318548', '318549', '318566', '318570', '318572', '318573', '318574', '318575']
nosy_count = 5.0
nosy_names = ['rhettinger', 'facundobatista', 'mark.dickinson', 'skrah', 'serhiy.storchaka']
pr_nums = ['7355', '7356', '7357']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue33750'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[serhiy-storchaka]

$ ./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
?          ^^

---

[skrah]

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.

[serhiy-storchaka]

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?

[skrah]

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.

[skrah]

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.

[serhiy-storchaka]

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

[skrah]

New changeset e95dfc5 by Stefan Krah in branch 'master':
bpo-33750: Reset thread-local context precision in test_round(). (bpo-7355)
e95dfc5

[skrah]

New changeset 7f1bcda by Stefan Krah (Miss Islington (bot)) in branch '3.6':
bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) (bpo-7356)
7f1bcda

[skrah]

New changeset bdab3ea by Stefan Krah (Miss Islington (bot)) in branch '3.7':
bpo-33750: Reset thread-local context precision in test_round(). (GH-7355) (bpo-7357)
bdab3ea

[skrah]

OK, thanks for checking the other tests!