What is the cross between the progeny of $F_1$ and the homozygous recessive parent called? How is it useful?

(N/A) The cross between the progeny of $F_1$ and the homozygous recessive parent is called a test cross.
It is useful for determining the genotype of an organism showing a dominant phenotype. By crossing an individual with an unknown genotype (showing a dominant trait) with a homozygous recessive individual,we can observe the phenotypic ratio of the offspring.
If all offspring show the dominant trait,the unknown parent is homozygous dominant. If the offspring show a $1:1$ ratio of dominant and recessive traits,the unknown parent is heterozygous.