In this pipeline, a specific container is started that clones the source code:

Running with gitlab-runner 11.8.0 (4745a6f3)
   on runner-gitlab-runner-7fd79f558b-2wx96 _drEv8rS
 Using Kubernetes namespace: gitlab-managed-apps
 Using Kubernetes executor with image gliderlabs/herokuish:latest ...

It will try to detect the language that's used. In our case, it finds a Ruby application, which is correct:

$ setup_test_db
 $ cp -R . /tmp/app
 $ /bin/herokuish buildpack test
 -----> Ruby app detected
 -----> Setting up Test for Ruby/Rack
 -----> Using Ruby version: ruby-2.5.3
 -----> Installing dependencies using bundler 1.15.2

After installing the necessary dependencies, it will run the rake test task:

-----> Running test: bundle exec rspec
 ...
 Finished in 0.03197 seconds (files took 0.22688 seconds to load)
 3 examples, 0 failures

In our case, no errors were detected. You can check which tests are run in your tests folder.

Of course, the tests that are run are written by yourself, so you determine how much value they have. When they are finished, the next stage is to deploy to production, which is covered in the next section.