What is a chemistry test?

Question

In the context of casting for a movie, what is a chemistry test and how is it performed?

Answer 1

It test how two actors can relate to each other. Generally the male and female lead.

Here's a good article about the same The Chemistry Test.

Apparently the producers and studios want to be absolutely sure that the lead actors have chemistry, otherwise known as attraction, compatibility, comfort and any other vague quality that might translate to the movie.