Fix the unit tests

[imagine-consortium]

Fix the unit tests

[1313e]

The remaining tests in old_tests must still be converted though.

[luizfelippesr]

The tutorials listed in the docs provide a good set of tests. Perhaps, they should be integrated in the (full) test set through something like nbval

[1313e]

Should the tests also be rewritten to pytest?

[luizfelippesr]

I don't think there is anyone against it. So, aye!

[luizfelippesr]

c337c43

[luizfelippesr]

Testable templates

With minor modifications, the (subclass) template files could become testable. This would be useful in a number of ways, in particular:

1. templates are meant to be the starting point for new IMAGINE users, so it is important that they are up-to-date and working;
2. templates are supposed to exemplify most or all of the functionality available, so by testing them we will be testing most or all the features that can be used.

[luizfelippesr]

(I will give the above idea a try while testing the modifications introduced while working on #38)

[1313e]

I did update the templates though to reflect the changes I made to all the base classes.

[luizfelippesr]

f02ade3

[luizfelippesr]

A test for PipelineTemplate is still missing.