Decorators should be compatible with no call syntaxe

Currently decorating a method `runTestInSlicerContext` without call args will incorrectly mark the test as successfully run when run from the Slicer widget env.

Locate the decorator applied to runTestInSlicerContext and inspect how it behaves when used without call arguments. Reproduce the case from the Slicer widget environment and verify that the test is not reported as successfully run unless it actually executes; add or update regression coverage where the existing tests for this decorator are located.

Written by the indexing model from the issue text.