Revert "CI: Remove test coverage"

This reverts commit d99e139c6b.

.gitlab-ci.yml

@@ -125,7 +125,13 @@ unit-testing:
   script:
     - mix ecto.create
     - mix ecto.migrate
-    - mix test --preload-modules
+    - mix test --cover --preload-modules
+  coverage: '/^Line total: ([^ ]*%)$/'
+  artifacts:
+    reports:
+      coverage_report:
+        coverage_format: cobertura
+        path: coverage.xml
 
 unit-testing-erratic:
   extends:

mix.exs

@@ -190,6 +190,7 @@ defp deps do
       {:ex_machina, "~> 2.4", only: :test},
       {:credo, "~> 1.6", only: [:dev, :test], runtime: false},
       {:mock, "~> 0.3.5", only: :test},
+      {:covertool, "~> 2.0", only: :test},
       {:hackney, "~> 1.18.0", override: true},
       {:mox, "~> 1.0", only: :test},
       {:websockex, "~> 0.4.3", only: :test},