How is the unknown genotype determined in a
test cross?

Look below :))

Explanation:

A testcross will determine the organism's genotype. The unknown genotype can be determined by observing the phenotypes of the resulting offspring. ... If any recessive phenotypic individuals result from the cross, then the unknown individual must carry the recessive allele, and have the heterozygous genotype.

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.