Variables assigned in the inspector of a script don't seem to work when instantiating them via AddComponent

that's my little test script. when i attach it to a game-object manually, test2 is not null, but when i attach it using AddComponent, it is. is there a way to get that to work?

alternatively, i could move the texture into the resources folder and load it based on a string, but that would make setting the icon for each of my items a bit more work. ;) is there a better alternative?

another question: why do test and test3 in that script not show up in the inspector? they both show up in the inspector when the script is attached to a game-object: