You should test your extension in the distros which you want to support.
Here is the distro list:
- Ubuntu 12.04 and higher
- CentOS 6.5 and higher
- Oracle Linux 6.4.0.0.0 and higher
- openSUSE 13.1 and higher
- SUSE Linux Enterprise Server 11 SP3 and higher
- FreeBSD
- CoreOS
You can choose some or all of them to support.
It's important to understand that Azure currently has two deployment models: Resource Manager, and classic. Make sure you understand deployment models and tools before working with any Azure resource.
If you decide to support the scenario of deploying your extension using ARM Templates, you need to test it.
There are many tools to do the CI work, for e.g. Jenkins, Concourse and so on.