The study presents linguistic tests for diagnosing Zeno Wendler’s verb classes, illustrated by selected Bulgarian verbs. The tests are divided into three groups, according to grammatical aspectuality, durativity and telicity, and agentivity. The research reveals that tests which rely on semantic compatibility at the lexical level (and not on semantic compatibility between lexical and grammatical level) are applicable for both English and Bulgarian. The research methodology is also based on Emmon Bach’s and David Dowty’s classifications of verb classes in which stage-level and individual-level predicates are distinguished, with a focus on agentivity in Dowty’s approach, as well as on Donald Davidson’s representation of action verbs as predicates with a hidden event argument, which has been refined by Claudia Maienborn to include a formal description of state predicates representing the ontological difference between two kinds of states: state verbs that denote true Davidsonian eventualities (Davidsonian states) and stative verbs that resist a Davidsonian analysis (Kimian states). These theoretical considerations allow to describe states as a heterogeneous class and provide reliable means for distinguishing different types of states.