When you run the custom tool of a T4 Template, it generates code in a child node of that template. On StackOverflow I have seen a a lot of devs asking how to write to separate files, or even to a different folder. This is actually easy to achieve, and there are multiple possible solutions.
When working with T4 templates in Visual Studio, you have to manually execute the custom for it to trigger the code generation. I used AutoT4 in the past (a VS2012 extension) to execute template on build time but this extension is not supported in the latest version(s) of Visual Studio. T4Executer is open for contributions
This is not so hard to do actually. It ensures your transformations are executed when you build your solution, when in some cases you did not click ‘Build > Transform all T4 Templates’ when changes are made to your .tt files. If one of your projects uses T4 to generate code, and you want it