Ok, i always had troubble with Signals, i hope at some point in my life i will understand this.

But how does your Mod work ? I installed it, but there is just a little T Symbol. But what can i do with it ?

I should write a how to use guide. heres the short version. it assumes you have a junction blueprint you want to test.
Go to start new game.
one of the options down the side will be "RailTester/AutoTester"
when you load into the map, you will have a control pannel window (the T symbol button shows/hides this window while on this map)
get the blueprint you want to test, (either via blueprint storage, or blueprint string), and with the blueprint in your hand click the start button on the control pannel
if you have several blueprints to test, instead put them all in the chest in the middle of the map, then press start (blueprints will be tested one after another and results will go to the factorio log file)

thx, will try