Test works normally but fails under pytest with assertion rewriting #4412
Description
Given a test file p.py containing:
def test_add():
add = lambda *t: sum(t)
l = range(8)
e = iter(l)
assert sum(l[:4]) == add(*[next(e) for j in range(4)])the test doesn't work under pytest with assertion rewriting. Note that the expression on the rhs of == will return a different result when evaluated a second time. The first time it is evaluated it will give 6 and the second time 22.
The test passes (as expected) when imported normally:
>>> import p
>>> p.test_add()It also works under pytest without assertion rewriting
$ pytest p.py --assert=plain
==================================================================== test session starts =====================================================================
platform darwin -- Python 3.6.2, pytest-3.10.0, py-1.7.0, pluggy-0.8.0
rootdir: /Users/enojb/current/sympy/sympy, inifile:
plugins: faulthandler-1.5.0
collected 1 item
p.py . [100%]
================================================================== 1 passed in 0.01 seconds ==================================================================However it fails under pytest with assertion rewriting
$ pytest p.py
==================================================================== test session starts =====================================================================
platform darwin -- Python 3.6.2, pytest-3.10.0, py-1.7.0, pluggy-0.8.0
rootdir: /Users/enojb/current/sympy/sympy, inifile:
plugins: faulthandler-1.5.0
collected 1 item
p.py F [100%]
========================================================================== FAILURES ==========================================================================
__________________________________________________________________________ test_add __________________________________________________________________________
def test_add():
add = lambda *t: sum(t)
l = range(8)
e = iter(l)
> assert sum(l[:4]) == add(*[next(e) for j in range(4)])
E assert 6 == 22
E + where 6 = sum(range(0, 4))
E + and 22 = <function test_add.<locals>.<lambda> at 0x10454e048>(*[0, 1, 2, 3])
p.py:6: AssertionError
================================================================== 1 failed in 0.08 seconds ==================================================================