Scholarship in language testing is increasingly embracing sociologically defined notions of language. This includes the notion of interactional competence (IC) which encompasses the various sequential, temporal, and embodied resources language learners utilize when interacting in the L2. This paper makes a contribution to scholarship that seeks to connect terminological and conceptual aspects of interaction research and research in language testing. To that end, this paper focuses on what is regular and structural about human talk-in-interaction, what it is that differentiates human interaction from prescriptively normative notions language professionals often apply to sentence-level lexis and grammar, and why including notions of interactional competencies is desirable in language testing. If language testing is to systematically target actual interactional abilities of L2 learners, then it is useful to examine what it is that makes interaction highly structured yet also dynamic to establish a conceptual basis for testing goals and practices.