Leung and Lewkowicz remind us that the debate over the past two decades that is most relevant to ELT (English languge teaching) pedagogy and curriculum concerns test-task authenticity. This paper first reviews how the authenticity debate in the literature of second language acquisition, pedagogy and testing has evolved. Drawing on a body of research work on learner task-based language performance in recent years, the paper then discusses the four dimensions of test task that should help us locate and determine the relative degree of authenticity of a test task. It is further argued that these authenticity dimensions interact with each other, and may be variably manifested in a way that apparently involves a complex and dynamic process under different assessment conditions.