test/source_files seems dysfunctional in mulled tests

[bernt-matthias]

Seems that test/source_files does not work in mulled tests (the conda-build tests seem to work).

I guess that one would need to add --test-files here:

bioconda-utils/bioconda_utils/pkg_test.py

Line 151 in 1734a52

'--test', tests

..

[dpryan79]

The mulled tests only have access to files that are installed with the package rather than things shipped with the source code or recipe.

[corneliusroemer]

+1 one test/source_files not working with mulled tests. This is an important limitation compared to standard conda.

test/source_files are part of the package, so mulled tests should be able to access them.