© 2021 David Wei Dai ; This thesis documents the design and validation of a computer-mediated interactional competence (IC) test for L2-Chinese speakers. Adopting an argument-based approach to test validation, the researcher designed the test following a task-based needs analysis (TBNA), eliciting the perspectives from L2-Chinese speakers, L1-Chinese teachers and L1-Chinese interactants on what L2-Chinese speakers struggle the most with interpersonal interaction in L2 Chinese. Findings from the TBNA informed the design of a nine-item IC test that targets test-takers’ ability to manage disaffiliative social actions, is delivered on a mobile-phone application, covers three sub-language use domains (everyday life, work and study) and includes three degrees of interactiveness in terms of task methods (1st pair part voice messaging, 2nd pair part voice messaging and live video chat). The specification of the IC test construct and development of the rating scale were based on everyday-life domain experts’ indigenous criteria on IC. 36 domain experts listened to and commented on 22 pilot test-takers’ performances on the test. A thematic analysis on domain experts’ interview transcripts and written comments returned five indigenous categories that formed the five rating categories in an indigenous IC scale. Analysing pilot test-taker discourse through Conversation Analysis and Membership Categorisation Analysis, the researcher theorised the a-theoretical indigenous rating scale into a theorised IC scale, which has disaffiliation management, affiliative resources, morality, reasoning, and role enactment and orientation as its five rating categories. 105 test-takers participated in the main testing study, whose performances were rated in a fully-crossed design by two raters using the theorised IC rating scale. Many facet Rasch analysis on rating results showed that item performance, rater reliability and rating scale functioning were satisfactory. Correlational analyses on test-takers’ IC test performance and an external ...