Is one halachikly allowed to learn for a test or exam on shabbat. for example reading his text book or notes? Would this be considered as preparing for after shabbat?

If you don't say explicitly it is for your test after Shabbat you can. (Shmirat Shabbat Kehilchata 28; 84. see also footnotes 206, 169) However, there are better things Shabbat can be used for. (Beit Yosef 290 [2])