Regarding the importance and complexity of writing among the EFL language learners, this study explored the learners' attitudes toward teaching and testing writing through Computerized Dynamic Assessment (CDA). The participants of this study were 22 Iranian upper-intermediate EFL learners. All the participants were adults and participated in this study voluntarily. To meet the aim of the study, the researchers developed software which contained 11 series of multiple-choice questions tests. Throughout each test, participants received feedback based on their needs and within their Zone of Proximal Development (ZPD). After each session and test, the learners were required to write down their attitudes toward the effectiveness of CDA in teaching and testing writing. The participants wrote their attitudes in a form of diary. At the end, their diaries were analyzed and it was revealed that all the learners had positive attitudes toward the implementation of CDA in teaching writing.