An assay or test method is a definitive procedure that produces a test or assay result.
A test can be considered as technical operation that consists of determination of one or more characteristics of a given product, process or service according to a specified procedure. Often a test is part of an experiment.
The test result can be qualitative (yes/no), categorical, or quantitative (a measured value). It can be a personal observation or the output of a precision measuring instrument.
Usually the test result is the dependent variable, the measured response based on the particular conditions of the test or the level of the independent variable. Some tests, however, involve changing the independent variable to determine the level at which a certain response occurs: in this case, the test result is the independent variable.
Freely elaborated from: Wikipedia