Test cross is a method devised by Mendel to determine the genotype of plant with dominant phenotype (purple flower in this case). In a test cross, the unknown dominant genotype is crossed with recessive parent (white, W in the given case).
(i) If the progeny consists of purple and white flowers in ratio of 1:1, the purple flower is a hybrid with PW genotype. It can be seen from the given cross.
(ii) If the progeny obtained have all purple flowers, both parents are homozygous, i.e. genotype of purple flower is PP. It can be seen from the cross that follows: