Many pedagogical assessments controlling knowledge and competences present themselves as mastery tests. They indeed intend to evaluate achievement stated as objectives to attain by the curriculum, and are often considered as a prerequisite to further learning. Firstly, we demonstrate that the methods frequently used in the elaboration of these kinds of tests are hardly adequate. They strongly encourage eliminating of «too easy» items, although these can be of as great an interest as others to the didactician. We then illustrate the advantages of the generalizability model, using a detailed example (a grammar exam at University level). This model allows us to control the major docimological quality of a mastery test: its capacity to reliably differentiate learners who attain the set cut score from those who do not. It further offers a range of useful information for the development and the interpretation of the test.