Hello Roel,

Automated testing certainly is a huge topic, so it's easy to get lost just figuring out what exists out there. On top of this, most of the material you find is written for a different platform (not DataFlex), so you need to interpret and adapt, and very often you have to make your own tools. So a task that is already huge gets even bigger.

My journey into automated testing started over ten years ago by listening to developer podcasts (most notably Stackoverflow), and being influenced by people like "Uncle Bob" Martin and Kent Beck. So it's been a particular interest of mine for some time now. It certainly helps to have a good understanding of the fundamentals and origins of automated testing, but in order to get started in a relatively short time, my best recommendation is to take a trial subscription with Pluralsight and have a look at the automated testing courses there. The quality of the material is excellent, and IMHO it's the fastest way to get started.

Take a look at:
Testing Automation: The Big Picture
Automated Business Readable Web Tests with Selenium and SpecFlow

For webapp testing, you have an array of choices. Selenium is well suited for UI testing, but I would not recommend testing everything through the UI. That is too slow, and UI tests are brittle. (When you change something in the UI, you have to change a lot of tests that are really testing something unrelated to the change in UI). Also, when it comes to Selenium, you need to make a choice about what programming language you want to use to write the Selenium tests (C#, Java, Javascript are some alternatives).

As long as the back-end is written in DataFlex, I would recommend using DFUnit for testing your business logic.

But for automated testing to have any lasting value, you really need to have an automated build process. So my advice is to start there. I wrote a few lines about setting up Jenkins with DFUnit.