What is the test for allowing a party not before the court to assert their own rights?

Second, the principle of allowing one to assert the rights of another not before the court is narrowly construed. In determining this issue, the court must first inquire as to the relationship between the litigant and the parties whose rights he seeks to assert. "[T]he relationship between the litigant and the third party may be such that the former is fully, or very nearly, as effective a proponent of the right as the latter ..." Singleton v. Wulff, 428 U.S. 106, 115 (1976). Second, it must be determined whether an obstacle exists that would prevent the third party from asserting his right himself. Id.