Anantapur/ Vijayawada, June 12 (ANI): Polling is underway in the crucial by elections to 18 assembly segments and one Lok Sabha constituency in Andhra Pradesh. The by elections would be an acid test for the ruling Congress party facing a serious challenge from the emerging YSR Congress party of YS Jaganmohan Reddy, presently in jail on charges of corruption. With all major political parties including Congress, Telugu Desam Party (TDP), YSR Congress party, Bharatiya Janata Party (BJP), Lok Satta and TRS fielding their candidates, the fight in majority of the seats has become either three or multi cornered contests.