Incorrect indentation of docstrings in code displayed in assert failures

[VorpalBlade]

The indentation in the displayed code is incorrect for docstrings in class members in the assertion errors.

$ py.test
===================================== test session starts =====================================
platform linux -- Python 3.5.2, pytest-3.5.1, py-1.5.3, pluggy-0.6.0
rootdir: /home/user/tmp, inifile:
collected 2 items                                                                             

test_dummy.py FF                                                                        [100%]

========================================== FAILURES ===========================================
___________________________________________ test_a ____________________________________________

    def test_a():
        """Foo bar
        quux
        """
>       assert False
E       assert False

test_dummy.py:6: AssertionError
______________________________________ TestClass.test_b _______________________________________

self = <test_dummy.TestClass object at 0x7fd93fbefa58>

    def test_b(self):
        """Foo bar
            quux
            """
>       assert False
E       assert False

test_dummy.py:13: AssertionError
================================== 2 failed in 0.03 seconds ===================================

Notice the extra indentation in the error report for test_b. (See the attached file for the code, had to add .txt to make github accept the file though.)

test_dummy.py.txt

System information:

$ pip list
Package        Version
-------------- -------
attrs          18.1.0 
more-itertools 4.1.0  
pip            10.0.1 
pkg-resources  0.0.0  
pluggy         0.6.0  
py             1.5.3  
pytest         3.5.1  
setuptools     39.2.0 
six            1.11.0 
$ uname -a
Linux tmgarn 4.4.0-124-generic #148-Ubuntu SMP Wed May 2 13:00:18 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
$ cat /etc/os-release 
NAME="Ubuntu"
VERSION="16.04.4 LTS (Xenial Xerus)"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 16.04.4 LTS"
VERSION_ID="16.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
VERSION_CODENAME=xenial
UBUNTU_CODENAME=xenial

[pytestbot]

GitMate.io thinks possibly related issues are #1 (assert reinterpretation fails for some code layouts), #61 (Assert rewriting failure for multiple 'and'), #577 (assert rewritereinterp failure with tripple quotes), #7 (assert failure inside doctest doesn't prettyprint), and #715 (Full diff of sequences should be displayed on assertion failures when verbose).

[nicoddemus]

Thanks @VorpalBlade for the report!