This paper contextualizes language tests in relation to educational and national language policies by demonstrating how these language measures may be used as mechanisms for affecting "de facto" language policies. This phenomenon is of special relevance given current controversies in nation states between multilingual and multicultural realities and government policies that perpetuate homogenous policies with regard to national languages. The introduction of language tests in certain languages delivers messages and ideologies about the prestige, priorities and hierarchies of certain language(s), and not others, leading to policies of suppression of diversity. Tests also influence language policy with regard to the nature of language, as derived from the criteria used for judging language quality via rating scales, guidelines and frameworks, thus leading to a view of language as standardized and homogenous. Yet language tests, when they incorporate research findings about language learning and language use, can serve as tools for creating more valid and real language policies that mediate and negotiate between ideology and practice. The discussion of these issues is supported by examples from a range of international contexts in this paper. (Contains 3 figures.)