Test cross is crossing between
(a) Genotype with the dominant trait.
(b) Genotype with the recessive trait.
(c) ${ F } _{ 1 }$ hybrid with double recessive.
(d) Two ${ F } _{ 1 }$ hybrids.

Hint: This was first used by Gregor Mendel in his experiment related to plant hybridization. He used this cross to determine the genotype of the ${ F } _{ 1 }$ hybrid by crossing it with the individual having suppressed traits.

Complete answer:
A test cross is a crossing between the F1 generation hybrid(Yy) or (YY) and a double recessive parent(yy). This cross helps us in determining the genotype of the ${ F } _{ 1 }$ hybrid.
If the ${ F } _{ 1 }$ hybrid is expressed as a dominant phenotype then there will be the possibility of carrying two types of traits or allele one in which it is carrying homozygous dominant traits(YY) and the second one in which it is carrying heterozygous dominant traits(Yy).
In the case of an ${ F } _{ 1 }$ hybrid with homozygous dominant traits(YY) or phenotype, if it is test crossed with homozygous recessive traits(yy), then the result will be that all the progeny will show the heterozygous dominant phenotype (Yy, Yy, Yy, Yy).
In the case of an ${ F } _{ 2 }$ hybrid with heterozygous dominant traits (Yy) or phenotype, if it is test crossed with homozygous recessive traits(yy), then the result will be that half or ${ 50 }$% of the progeny will show the heterozygous dominant phenotype(Yy, Yy) and the remaining half or ${ 50 }$% of the progeny or offspring will show the homozygous recessive phenotype (yy, yy).

So, the correct answer is, '${ F } _{ 1 }$ hybrid with double recessive'.

Note:
-Mendel’s work was rediscovered in the early 1900s(between1908-1911) that led to an explosion of experiments employing the principles of test crosses, these experiments were conducted by Thomas Hunt Morgan and later became hallmarks in the discovery of sex-linked traits. became hallmarks in the discovery of sex-linked traits.
-For the determination of genotype more advanced techniques have been developed such as Genetic testing and genome mapping that made the test cross-less prevalent in genetics.