The Supreme Court of the United States delineated the test for the availability of interlocutory appeals, called the collateral order doctrine, for United States federal courts in the case of Lauro Lines s.r.l. v. Chasser, 490 U.S. 495 (1989), holding that under the relevant statute (28 U.S.C. § 1291) such an appeal would be permitted only if:

1. the outcome of the case would be conclusively determined by the issue;
2. the matter appealed was collateral to the merits; and
3. the matter was effectively unreviewable if immediate appeal were not allowed.