The literature on C-test and Cloze test in a second language provides us with few accounts of the real mental processes that test-takers are involved in, which in fact indicate the real nature of what these tests measure. However, the literature leaves researchers with little attention to the cognitive processes involved in X-Tests. Therefore, the purpose of this study was to discover the extent to which the C-Test and the X-Test tap participants' use of mental strategies. In doing so a C-Test and an X-test were administered to eight subjects who were EFL learners in Mashhad, Iran. They all took part in introspective methods of think-aloud and retroactive interviews throughout the test administration. Think aloud protocol was used to collect the required data. The results showed that both tests were similar to each other regarding mental processes, except in using two strategies that participants applied only for filling out the gaps of the X-Test. Moreover, it appeared that the X-Test was more difficult for the subjects.