Aunt/Uncle (Avuncular) testing can be useful for establishing a relationship in situations where the parents are not available to be tested. It can be used to examine the relationship between a child and a possible aunt or uncle, although the inclusion of other close relatives in the test is always recommended.
It is possible to just compare the DNA profile of a child and an alleged aunt or uncle (although we prefer that the mother is tested). This can provide an indication of a relationship but, because of the patterns of DNA inheritance, it will not always reveal the true nature of the relationship. Such an analysis can only report the most likely relationship given the DNA evidence.