Language assessment or language testing is a field of study belonging to the umbrella of applied linguistics. A test is a smaller part of assessment, intending to measure the respondents’ knowledge or other abilities. It is a very important process after working or learning time. There are six qualities of useful tests, including reliability, validity, authenticity, interactiveness, impact, and practicality.

First of all, reliability is defined as consistency of measurement, the degree to which an assessment tool produces stable and consistent results (Phelan, 2005-2006). In other words, the test consistently comes to the same results different situations. Also, it is a prerequisite for validity (Gonzalez, 1996). Some types of reliability are: test reliability, rater reliability, and parallel forms reliability, and internal consistency reliability.
Test reliability is a measure of reliability obtained by administering the same test twice over a period of time to every member in a group. The scores from the first time and the latter can then be correlated in order to evaluate the test for stability over time. For example, a test designed to assess student learning in reading comprehension could be given to a group of students twice, with the second administration perhaps coming a week or two weeks after the first. The obtained correlation coefficient would indicate the stability of the scores.
Rater reliability, which is concerned in human error, subjectivity, and bias, may