Run tests inside Docker container with Jenkins

[Yevhenii Kurtov]

We want to give it a try to setup CI/CD with Jenkins for our project. The project itself has Elasticsearch and PostgreSQL as runtime dependencies and Webdriver for acceptance testing.

In dev environment, everything is set up within one `docker-compose.yml` file and we have `acceptance.sh` script to run acceptance tests.

After digging documentation I found that it's potentially possible to build CI with following steps:

1. dockerize project 

2. pull project from git repo

3. somehow pull `docker-compose.yml` and project `Dockerfile` - either:

 * put it in the project repo

 * put it in separate repo (this is how it's done now)

 * put somewhere on a  server and jut copy it over

4. execute `docker-compose up`

5. project's Dockerfile will have `ONBUILT` section to run tests. Unit tests are run through `mix tests` and acceptance through `scripts/acceptance.sh`. It'll be cool to run them in parallel. 

6. shutdown `docker-compose`, clean up containers

Because this is my first experience with Jenkins a series of questions arise:

- Is this a viable strategy? 

- How to connect tests output with Jenkins?

- How to run and shut down docker-compose? 

- Do we need/want to write a pipeline for that? Will we need/want pipeline when we will get to the CD on the next stage? 

Thanks