In order to improve the soundness of the kinetic analysis of solid-state reactions, we present an experimental test based on a sudden change (jump), during an experiment, of the temperature, or of the partial pressure of gases, which have an influence on the kinetic rate. This test, denoted "f(α) test" allows to discriminate if the kinetic modelling may or may not involve the rate equation dα/dt = kf(α) for any kind of reaction: thermal decomposition, solids reacting with gases, ... Numerous examples are given and discussed according to the answer of the test, mainly based on the consideration of nucleation and growth processes.