One of the basic terms in classical statistics and probability theory. In the axiomatic approach it is defined as any decomposition of the space of elementary events into pairwise-disjoint events, which are called "initial tests" , while the elements of the $\sigma$-field generated by them are called "events related to the given test" . The term "testing" is basically used in combinations as "repeated testing" , "independent testing" , "testing in a Markov chain" .
This terminology for such a simple concept is hardly ever used in the West.