Finally, a test measures a given domain. For example, in the case of a proficiency test, even though the actual performance on the test involves only a sampling of skills, the domain is overall proficiency in a language-general competence in all skills of a language. Other tests may have more specific criteria. A test of pronunciation might well be a test of only a limited set of phonemic minimal pairs. A vocabulary test may focus on only the set of words covered in a particular lesson or unit. One of the biggest obstacles to overcome in constructing adequate tests is to measure the desired criterion and not include other factors inadvertently, an issue that is addressed in Chapters 2 and 3