Unit test buildup

Adds full unit tests for discoto. Coverage is at ~84% now, fixed a handful of errors that were causing issues.

Checklist

• Manually verified passing unit tests for this branch locally by running bin/run_docker_tests.sh
  • Yes, this is a pain, but GitLab doesn't run reasonably within a docker container in a normal CI pipeline
  • See bin/run_docker_tests.sh --help for faster/iterative testing options
• Paste local test output

Local Test Output

/bin/run_docker_tests.sh output

bin/run_docker_tests.sh --no-kill
[>>>] Will not kill docker container (can be re-used)
[>>>] Retrieving token
[>>>] GitLab should be ready
[>>>] Pasteable config into bin/.env: 
[>>>] 
export DISCOTO_GITLAB_ENDPOINT=http://172.17.0.4
export DISCOTO_GITLAB_TOKEN=-8K2oWSYStQaxKx3D3Q-
export DISCOTO_PROJECTS=test-group/test-project
export DISCOTO_GROUPS=test-group
export DISCOTO_ISSUABLE_ASSIGNEE=
export DISCOTO_ISSUABLE_AUTHOR=
export DISCOTO_ISSUABLE_LABELS=discoto
[>>>] 
[>>>] Running tests on unit-test-buildup @ 3f4db6c26c5edeafdc21f5ae043bf57fa744f545
warning: parser/current is loading parser/ruby27, which recognizes
warning: 2.7.1-compliant syntax, but you are running 2.7.2.
warning: please see https://github.com/whitequark/parser#compatibility-with-ruby-mri.
....................................

Finished in 1 minute 27.69 seconds (files took 0.39873 seconds to load)
36 examples, 0 failures

Coverage report generated for RSpec to /home/james/ws/dev/gitlab/discussion-automation/coverage. 553 / 653 LOC (84.69%) covered.
[>>>] Cleaning up
[>>>] Cleaning up