Two hs tests use @requires as shown below:
gc/arguments/TestObjectTenuringFlags.java: * @requires vm.gc=="Parallel"
gc/arguments/TestInitialTenuringThreshold.java: * @requires vm.gc=="Parallel"

such usage is not correct, because those test will not be run if no collector is specified.

The purpose of "@requires" is to protect a test from running in not applicable configuration, such as:
- conflicting collector
- wrong OS
- not enough memory
- product/debug build

The right expression should look like:
@requires vm.gc=="Parallel" | vm.gc=="null"