For wired decoders I used always used a test fixture of some sort in case I wanted to test it before installation or in case I had issues with it and wanted to test it separately. In the February 2011 post Building a decoder tester I showed how I built the one I am currently using.
Of course now there are many decoder models that have no wires. I wanted to come with with some sort of easy connections to my decoder tester to accommodate those. The first one I have done is for the TCS CN and CN-GP decoders as I use a lot of those.
This setup should also work on with the TCS MT1500 decoder.