Workday offers a Workday Studio application (called "Eclipse") that allows you to test integrations using Workday's very own integration infrastructure. It has been designed for developers. 

Here I document my steps in installing Workday Studio on my Mac OS.

Workday describes it as being:

• Run your Workday Studio integrations like any other Workday integration - configure, launch, schedule, monitor, and even audit your integrations.
• Use powerful and productive development tools optimized for interacting with your Workday tenant.
• Build sophisticated and highly customizable integrations without the need to own or manage any on-premise integration middleware or servers.

Source: Workday Studio - https://community.workday.com/studio

If you're looking to add your app to the Microsoft Azure AD (Active Directory) application gallery here's a quick guide on how I have submitted an app there.

This aims to supplement the guide from the Azure team on how to List your app to the Azure application gallery.

So, let's give you a sense of what we are talking about here and then I can walk you through how I submitted an app to the Azure AD application gallery.