The following suggests that the limbs may be of a (legal) test and applied to a case (or simply to a case for short). I suspect that the limbs constitute or are comparable to a singular check-list or decision-tree (the test) that was developed for use in many different cases. So, they would be the test's limbs, not the case's limbs.
In contrast, the Federal Court in other cases has identified Perera as having two cumulative limbs and applied both limbs to the case at hand. For example, Carr J in Waiz v MIMA identified the two limbs and stated that the correct approach was whether the applicant could be said to have been effectively prevented from giving his evidence in relation to a matter of significance for his claim or the Tribunal decision. Mansfield J in Arif v MIMA and Goldberg J in Mahzar v MIMA also dealt with both limbs of the test formulated in Perera.
Legal tests are various kinds of commonly applied methods of evaluation used to resolve matters of jurisprudence. In the context of a trial, a hearing, discovery, or other kinds of legal proceedings, the resolution of certain questions of fact or law may hinge on the application of one or more legal tests.
Legal tests are often formulated from the logical analysis of a judicial decision or a court order where it appears that a finder of fact or the court made a particular decision after contemplating a well-defined set of circumstances. It is assumed that evaluating any given set of circumstances under a legal test will lead to an unambiguous and repeatable result.