Validation and verification of security policies is a critical and important task to ensure that access control policies are error free. The two most common problems present in access control policies are: inconsistencies and incompleteness. In order to detect such problems, various access control policy validation mechanisms are proposed by the researchers. However, comprehensive analysis and evaluation of the existing access control policy validation techniques is missing in the literature. In this paper, we have provided a first detailed survey of this domain and presented the taxonomy of the access control policy validation mechanisms. Furthermore, we have provided a qualitative comparison and trend analysis of the existing schemes. From this survey, we found that only few validation mechanisms exist that can handle both inconsistency and incompleteness problem. Also, most of the policy validation techniques are inefficient in handling continuous values and Boolean expressions.