A test measures performance , but the results imply the test-taker's ability or, to use a term common in the field of linguistics, competence. Most language tests measure one's ability to perform language, that is, to speak, write, read, or listen to a subset of language. on the other hand, it is not uncommon to find tests designed to tap into a test-taker's knowledge about language: defining a vocabulary item, reciting a grammatical rule, or identifying a rhetorical feature in written discourse. Performance-based tests sample the test-taker's actual use of language, but from those samples the test administrator infers general competence. A test of reading comprehension, for example, may consist of several short reading passages each followed by a limited number of comprehension question-a small sample of a second language learner's total reading behavior. But from the results of that test, the examiner may infer a certain level of general reading ability.