A test administered by the IRS to determine if a person qualifies as a dependant on someone else's tax return (such as a parent or guardian) and can thus receive a dependency tax exemption. The test stipulates that if someone is claimed as a dependent, that dependant cannot also file a joint return with their spouse in the same tax year. The exceptions to this rule are when the spouse files the tax return separately, when the person is not required to file a return, when filing only to receive a refund, or when neither spouse owes tax whether they file separately or jointly.