This study examined the effectiveness of assessment techniques applied in an online language learning context in a Sri Lankan university on the improvement of English as a Second Language (ESL) learning of a group of undergraduates. With the increasing integration of technology in education, traditional assessment methods are being replaced or supplemented by digital tools that offer interactive, flexible, and immediate feedback. This study investigated the assessment methods used in online ESL classes and undergraduates’ perception of the effectiveness of the assessment methods. It employed a qualitative case study approach to investigate this contemporary phenomenon using two data sources: semi-structured interviews with twelve undergraduates and the first author's reflective journal. Various digital assessment tools, such as online quizzes, discussion forums, e-portfolios, and gamified platforms like Kahoot!, were used in the assessments. The data were analyzed using thematic analysis, and the first theme includes the positive impact of the online examinations that contributed in terms of increased student engagement, motivation, and participation. The second theme included the impact of formative assessment methods, including instant feedback quizzes and peer evaluation, which were found to be highly effective in improving language skills. The third theme included challenges faced by the undergraduates including technical issues, limited digital literacy, and concerns regarding academic integrity. Some undergraduates reported difficulties in adapting to fully online assessments, while others expressed concerns about the fairness and reliability of them. Despite these challenges, the majority of participants preferred digital assessment methods over traditional approaches due to their flexibility and accessibility. This research suggests that digital assessment strategies are an important part of contemporary ESL teaching as they contribute to lifelong learning and skills acquisition. It suggests that the educators should implement a balanced approach between the formative and summative digital assessments, with sufficient training and support given to students.