We present a review of research related to the usability testing of mobile applications including participants with Down syndrome. The purpose is to identify good usability testing practices and possible guidelines for this process when participants are people with this cognitive disability. These practices and guidelines should account for their specific impairments. We applied document analysis techniques to searches of scientific databases. The results were filtered considering how well they matched the research topic. We processed and reported the classified and summarized results. The main findings of this literature review is that mobile applications usability testing including people with Down syndrome is an issue that has not be comprehensively investigated. While there is some related research, this is incomplete, and there is no single proposal that takes on board all the issues that could be taken into account. Consequently, we propose to develop guidelines on the usability testing process involving participants with Down syndrome.