This study aims to investigate two issues. Firstly, it explores English as a foreign language (EFL) high school teachers’ practices of testing and washback in teaching reading comprehension. Secondly, their perceptions of its washback effects are scrutinized. Content analysis, questionnaires, and semi-structured interviews were employed to collect data. Sixty teachers at some high schools in Can Tho City, Vietnam were contacted to answer the questionnaire. In the end, five of them were selected to take part in the interviews. The findings indicated that designing tests has a beneficial impact on reading for EFL learners in the areas of students' passion for reading, decreasing reading boredom, students' interest in reading text content, and students' development of thinking skills. It has an impact on the teachers' time allotment, teaching strategies, and instructional materials.