1 files changed, 26 insertions, 0 deletions
diff --git a/testing/web-platform/tests/custom-elements/state/state-css-selector.html b/testing/web-platform/tests/custom-elements/state/state-css-selector.html
index d29c927223..8ead8d7809 100644
--- a/testing/web-platform/tests/custom-elements/state/state-css-selector.html
+++ b/testing/web-platform/tests/custom-elements/state/state-css-selector.html
@@ -99,6 +99,32 @@
         assert_equals(getComputedStyle(mySibling).getPropertyValue('color'), 'rgb(255, 0, 0)');
     }, "state selector only applies to has() on given ident");
 
+    test(function(t) {
+        myCE.elementInternals.states.add('--green');
+        myCE.elementInternals.states.add('--green');
+        myCE.elementInternals.states.add('--green');
+        t.add_cleanup(() => { myCE.elementInternals.states.delete('--green') });
+        assert_true(myCE.elementInternals.states.has('--green'));
+        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(0, 255, 0)');
+        assert_true(myCE.elementInternals.states.delete('--green'));
+        assert_false(myCE.elementInternals.states.has('--green'));
+        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(255, 0, 0)');
+        assert_false(myCE.elementInternals.states.delete('--green'));
+    }, "states added multiple times counts as one");
+
+    test(function(t) {
+        myCE.elementInternals.states.add('--green');
+        myCE.elementInternals.states.add('--foo');
+        t.add_cleanup(() => { myCE.elementInternals.states.clear() });
+        assert_true(myCE.elementInternals.states.has('--green'));
+        assert_true(myCE.elementInternals.states.has('--foo'));
+        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(0, 255, 0)');
+        myCE.elementInternals.states.clear();
+        assert_false(myCE.elementInternals.states.has('--green'));
+        assert_false(myCE.elementInternals.states.has('--foo'));
+        assert_equals(getComputedStyle(myCE).getPropertyValue('color'), 'rgb(255, 0, 0)');
+    }, "style is invalided on clear()");
+
     </script>
   </body>
 </html>