eTests is a free software that can be used to offer web-based multiple-choice formative assessment questionnaires. The assessments are formative because each choice is linked with complementary information in the form of hints if the answer is incorrect or comments if the answer is correct. Instant feedback allows students to correct any errors or confirm their reasoning. The answers are recorded so that individual or group performance can be monitored. This transfers responsibility to the learners by helping them compare themselves with their peers. The teachers can perform an edumetric analysis of the distribution of the answers to detect resolution difficulties, which could be the sign of a cognitive obstacle in the learning process. Creating increasingly complex sequences of questions can refine the diagnosis of any such obstacles.