Test & document SKIP in generator constructor

Closes #1593

tests/SelfTest/UsageTests/Generators.tests.cpp

@@ -261,6 +261,10 @@ TEST_CASE("Copy and then generate a range", "[generators]") {
     }
 }
 
+#if defined( __clang__ )
+#    pragma clang diagnostic pop
+#endif
+
 TEST_CASE("#1913 - GENERATE inside a for loop should not keep recreating the generator", "[regression][generators]") {
     static int counter = 0;
     for (int i = 0; i < 3; ++i) {
@@ -305,9 +309,5 @@ TEST_CASE( "#2615 - Throwing in constructor generator fails test case but does n
     // this should fail the test case, but not abort the application
     auto sample = GENERATE( make_test_generator() );
     // this assertion shouldn't trigger
-    REQUIRE( sample == 0U );
+    REQUIRE( sample == 0 );
 }
-
-#if defined( __clang__ )
-#    pragma clang diagnostic pop
-#endif