LB-620: Document way to run specific integration tests

[ykchong45]

Problem

LB-620

The documentation lacks information on running a single test file.
It has been updated to provide clear instructions on executing a specific test file using the ./test.sh script.

Solution

1. Correct the function is_unit_db_running by fixing the container name queried in docker ps.
2. Remove the function is_unit_db_exists.
3. Adjust the logic so that when the test container is running, executing ./test.sh [path-to-test-file.py] only runs the specified test and then exits, while retaining the test container for later runs.

[pep8speaks]

Hello @ykchong45! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file listenbrainz/tests/integration/test_settings_views.py:

Line 116:1: W293 blank line contains whitespace

[MonkeyDo]

Hi @ykchong45 !
Thanks for opening a PR.

I am not clear as to what the changes to the three non-documentation files achieve, looking at the PR title.

The only required change is adding the optional [path-to-test-file.py] in the documentation as well as possibly in the comments explaining the usage in the test.sh file.
None of the other changes make sense in the context of the problem stated. Could you please explain what they do, and why they are part of the same PR?

[amCap1712]

LGTM, Thanks!