All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
It is obligatory for you to fast and not wait for the result of the test. Fasting is obligatory upon you even after verifying pregnancy. The Sharee’ah obligates the pregnant woman to fast, unless she fears harm to herself, her fetus, or both, then it is permissible for her not to fast, because the Prophet said: “Allah the Almighty has waived fasting and half of the prayer for the traveler, and has waived fasting for the pregnant and the breastfeeding woman.” [An-Nasaa’i and At-Tirmidhi]
Ibn Qudamah said in Al-Mughni: The sum of this is that if the pregnant or the breastfeeding woman fears harm on herself, she may break the fast, and she only must make it up, and we do not know any difference of opinion among scholars regarding this, because they are like the sick person who fears for himself.
And the fear of harm is proven by a doctor, experience, or assumption.
Allah knows best.