A test that is used to determine if the mutation associated with a given phenotype is due to mutations in two different genes or due to different alleles of the same gene is called a complementation test.
A complementation test is also called as a cis-trans test.
If the mutations in a complementation test are located on the same position then the genes are termed as being on the cis position otherwise on the trans-position.
A cis test, that is if the genes are located on the same position serves as a control for the complementation test.
