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

tests/SelfTest/UsageTests/Skip.tests.cpp

@@ -71,3 +71,30 @@ TEST_CASE( "failing for some generator values causes entire test case to fail",
         FAIL();
     }
 }
+
+namespace {
+    class test_skip_generator : public Catch::Generators::IGenerator<int> {
+    public:
+        explicit test_skip_generator() { SKIP( "This generator is empty" ); }
+
+        auto get() const -> int const& override {
+            static constexpr int value = 1;
+            return value;
+        }
+
+        auto next() -> bool override { return false; }
+    };
+
+    static auto make_test_skip_generator()
+        -> Catch::Generators::GeneratorWrapper<int> {
+        return { new test_skip_generator() };
+    }
+
+} // namespace
+
+TEST_CASE( "Empty generators can SKIP in constructor", "[skipping]" ) {
+    // The generator signals emptiness with `SKIP`
+    auto sample = GENERATE( make_test_skip_generator() );
+    // This assertion would fail, but shouldn't trigger
+    REQUIRE( sample == 0 );
+}