Fix bug when an AttributeError is raised, and add unit tests for xtrigger

[kinow]

@dwsutherland, @hjoliver here are the unit tests for get_func, and that part of the SuiteConfig code that checks if the Xtrigger function is a callable.

One of the final unit tests was to check what would happen if we got an AttributeError, instead of an ImportError/ModuleNotFoundError. That is possible when you have a Xtrigger file cylc.py but without the cylc() function (I believe xtrigger module and function name are expected to match).

@dwsutherland I reckon this AttributeError would also cause the suite to hang? That error was propagated, instead of a SuiteConfigError, so I included a commit in this pull request to catch that error as well.

Now wait for Travis. Took a bit longer because decided to write using pytest instead of unittest the new test for cylc.config and because also decided to cover the AttributeError branch of get_func (second if statement in that function I think).

If approved, will prepare a back port for 7.8.x.

Cheers
Bruno

[dwsutherland]

Related back port of the fix is here:
#3059

And for some reason the Travis unit test is failing... No obvious error I can see

[kinow]

@dwsutherland added onre more commit. Codacy was complaining about the assert statements. These assert statements are definitely bad in production, but they are the de-facto way of writing assertions in PyTest.

So added a .codacy.yml file excluding all our unit test folders (for cylc and for parsec), as well as non source code files (licences folder, etc folder, etc).

This should speed up Codacy, and prevent it of reporting issues in isodatetime, doc folder, etc. (even though most of these exclusions will disappear with time, as we progress towards Cylc 8, setup.py, etc)

[kinow]

Codacy is now happy! Just waiting for Travis now 🎉

[hjoliver]

(I believe xtrigger module and function name are expected to match).

yup

[dwsutherland]

Looks good! thanks for the tutorial, I need to write more of these 😁

[kinow]

Thanks @dwsutherland ! And a FYI, I push-forced to edit the last commit, as the .codacy.yml was missing a break line after the last line with content. If anything blinks, it must be a flaky test and Travis will need a kick 👍

[hjoliver]

LGTM 👍

[hjoliver]

If approved, will prepare a back port for 7.8.x.

Still need this @kinow ?

[kinow]

Yup @hjoliver , preparing one now. Was just waiting for David's other back port to go first. Will rebase my 7.8.x branch, cherry pick and prepare a backport for this one. Thanks!!