The field of ESP language testing seems to represent significant challenges for trainers. The challenges frequently lie in developing reliable assessment tools, balancing background knowledge and language proficiency in ESP tests, or choosing specific language skills and competencies which ought to be tested in particular fields of academic or professional activity. The aim of this article is to report on a study conducted among ESP teachers practising in a number of educational institutions in Poland. The research sought to investigate what challenges ESP teachers face in designing tests in the context of the subject specific approach in foreign language instruction.