The article presents the theoretical and methodological principles of developing and using case tasks as a means of assessing the formation of professional competencies of future teachers. The essence of case technology in higher education, types of pedagogical cases in the context of professional training of future teachers have been characterized. Modern scientific approaches to the essence of case testing as a form of control and self-monitoring of educational achievements of students have been defined. Considering the provisions of the competence approach in higher education institutions, the professional standard, the essential features, components of the professional competencies of a modern teacher have been revealed, in particular, considering the requirements of the «specialist» qualification category. Features of case tasks as a means of assessing the formation of professional competences of future teachers (competence, contextual character, technological ability, etc.), stages of construction of case tasks (preparatory, pilot, expert), considering the type of pedagogical case, features of specific professional competence, level of general and professional training of future teachers have been presented. Examples of case tasks for assessing the formation of linguistic and communicative competence of future teachers have been given.