Check and extend regression tests

[olexandr-konovalov]

No description provided.

[olexandr-konovalov]

There are currently some diffs in the package tests when they are run with the stable-4.9 branch of the GAP repository. Please see https://travis-ci.org/gap-system/gap-docker-pkg-tests-stable-4.9-staging to inspect them: click on the line corresponding to this package and scroll till the very end of the log file to see the output of the package tests, the summary, and further instructions.

As soon as the package tests will run without diffs, they will be moved to https://travis-ci.org/gap-system/gap-docker-pkg-tests-stable-4.9. This will be very helpful to monitor in the future that the package is still usable and that no changes in the GAP system break the package.

[olexandr-konovalov]

Amazing, PR #6 increased code coverage by almost 90% :)

This is because of reading the library of Kurosh algebras.

[olexandr-konovalov]

Next goal: files in https://codecov.io/gh/gap-packages/modisom/tree/master/gap/nilalg currently have ZERO coverage.