Merge branch 'nahtnam/gitlab-ce-ci-test-phoenix' into 'master'

Add an example for testing a phoenix application with Gitlab CI

_Originally opened at !5074 by @nahtnam._

- - -

## What does this MR do?

Add an example on how to setup testing on phoenix 

## Are there points in the code the reviewer needs to double check?

Grammar and formatting

## Why was this MR needed?

https://twitter.com/gitlab/status/749898132008337408

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [ ] All builds are passing
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6794

CHANGELOG

@@ -10,6 +10,7 @@ v 8.13.0 (unreleased)
   - Add `/projects/visible` API endpoint (Ben Boeckel)
   - Fix centering of custom header logos (Ashley Dumaine)
   - ExpireBuildArtifactsWorker query builds table without ordering enqueuing one job per build to cleanup
+  - Add an example for testing a phoenix application with Gitlab CI in the docs (Manthan Mallikarjun)
   - AbstractReferenceFilter caches project_refs on RequestStore when active
   - Replaced the check sign to arrow in the show build view. !6501
   - Add a /wip slash command to toggle the Work In Progress status of a merge request. !6259 (tbalthazar)

doc/ci/examples/README.md

@@ -11,6 +11,7 @@ Apart from those, here is an collection of tutorials and guides on setting up yo
 - [Test and deploy a Python application to Heroku](test-and-deploy-python-application-to-heroku.md)
 - [Test a Clojure application](test-clojure-application.md)
 - [Test a Scala application](test-scala-application.md)
+- [Test a Phoenix application](test-phoenix-application.md)
 - [Using `dpl` as deployment tool](deployment/README.md)
 - [Blog post about using GitLab CI for iOS projects](https://about.gitlab.com/2016/03/10/setting-up-gitlab-ci-for-ios-projects/)
 - [Repositories with examples for various languages](https://gitlab.com/groups/gitlab-examples)

doc/ci/examples/test-phoenix-application.md

+## Test a Phoenix application
+
+This example demonstrates the integration of Gitlab CI with Phoenix, Elixir and
+Postgres.
+
+### Add `.gitlab-ci.yml` file to project
+
+The following `.gitlab-ci.yml` should be added in the root of your
+repository to trigger CI:
+
+```yaml
+image: elixir:1.3
+
+services:
+  - postgres:9.6
+
+variables:
+  MIX_ENV: "test"
+
+before_script:
+  # Setup phoenix dependencies
+  - apt-get update
+  - apt-get install -y postgresql-client
+  - mix local.hex --force
+  - mix deps.get --only test
+  - mix ecto.reset
+
+test:
+  script:
+    - mix test
+```
+
+The variables will set the Mix environment to "test". The
+`before_script` will install `psql`, some Phoenix dependencies, and will also
+run your migrations.
+
+Finally, the test `script` will run your tests.
+
+### Update the Config Settings
+
+In `config/test.exs`, update the database hostname:
+
+```elixir
+config :my_app, MyApp.Repo,
+  hostname: if(System.get_env("CI"), do: "postgres", else: "localhost"),
+```
+
+### Add the Migrations Folder
+
+If you do not have any migrations yet, you will need to create an empty
+`.gitkeep` file in `priv/repo/migrations`.
+
+### Sources
+
+- https://medium.com/@nahtnam/using-phoenix-on-gitlab-ci-5a51eec81142
+- https://davejlong.com/ci-with-phoenix-and-gitlab/