Hello Andrius Laukavičius,

             Yes, you can write tests using all new api stuff.

like,

from openerp.tests import common

class testPartnerCreate(common.TransactionCase):
    def setUp(self):
        super(testPartnerCreate, self).setUp()

    def test_create(self):
        res_partner = self.env['res.partner']

        test_partner1 = res_partner.create(
            dict(
                name="Demo bhai",
                city="test city",
                email="demo@test.com",
            ))

           ......

Hope this will help.

Regards....