What was the court's test in Illinois v gates to obtain a search warrant?

Illinois v. Gates deals with subsequent appellate review of probable cause, and is not a "test" dealing with application for a search warrant.

In reviewing PC, the court abandoned the two-pronged Aguilar-Spinelli test and instituted a "totality of the circumstances" standard instead.

The standard essentially lowers the burden on the State. Aguilar Spinelli made it nearly impossible to find PC on the basis of a confidential tip alone, so this test replaced it.