Test tubes work good to root plant cuttings in water. If you want to start with seeds it will be a bit more difficult but it can be done.
You'll need to add some growing medium to the test tube - for that you might want to make a small paper collar to act as a funnel to keep the soil away from the upper inside of the tubes. A chop stick is a handy tool to work with; helps to pack the planting medium and to place the seeds on the soil. The tricky part will be watering as you will have no drainage holes. There could be a problem with disease.
One of my children is a teacher and she showed me this classroom project; it's very basic as it is geared to 5 year old children but the basics are there. Starting the seeds in damp paper towels then transfering the seeds to the test tubes containing different growing media:
https://www.educationalinsight...
Good luck and hope you succeed.
