Fixes #1. Have tests inspect an exception's e.value instead of just t…

[twongCMU]

…he exception. pytest 5.0.0 no longer displays the custom text with str(e)

[twongCMU]

It looks like the CI tests fail due to #416 and not my changes

[twongCMU]

Bah. I fixed two issues in the forked branch, but when I submitted the pull request the links now refer to issues in this stingray repo's issue tracker, which is wrong. Anyway, here are the two issues I fixed:
twongCMU#1
twongCMU#2

[matteobachetti]

Hi @twongCMU, thanks a lot!

I'm not sure that the complete removal of conftest.py is what we want though. The fact that a line there makes everything fail doesn't make the whole file "unneeded".

An example of conftest.py compatible with the new pytest and astropy versions is here:
https://github.com/astropy/package-template/blob/master/packagename/conftest.py

[matteobachetti]

Hi @twongCMU, please see #415 for your second commit. You do not need to delete conftest.py, which is actually useful. I will merge #415 soon. After that, can you rebase to master and re-submit this PR with only the excinfo.value changes?

[pep8speaks]

Hello @twongCMU! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file ah_bootstrap.py:

Line 124:80: E501 line too long (92 > 79 characters)
Line 126:80: E501 line too long (98 > 79 characters)
Line 133:80: E501 line too long (86 > 79 characters)
Line 136:80: E501 line too long (93 > 79 characters)
Line 156:80: E501 line too long (88 > 79 characters)

• In the file stingray/conftest.py:

Line 15:80: E501 line too long (84 > 79 characters)
Line 16:1: E402 module level import not at top of file

[twongCMU]

Yes, I agree that it is better to keep conftest.py