Make it possible to run pytest

With the current setup we can't run pytest because the tests are not divided in frontend and bakend tests.

We could theoretically build a single container to run the tests but this would mean to build al fifth container.
Also bugs like the one fixed in #28 would not be detected by this.

Start by reviewing the current Docker container setup and how tests are divided between frontend and backend. The work is done when pytest can run with the available containers and detects regressions such as the bug fixed in issue #28.

Written by the indexing model from the issue text.