Make togglePopover throw more exceptions

This patch makes sure that togglePopover will throw exceptions when it
is disconnected from the document or doesn't have a popover attribute.

This is being discussed here: whatwg/html#8999

Change-Id: Iac7a486cd64b09b5657a157dbf3e9e54c1be2a27

html/semantics/popovers/togglePopover.html

@@ -44,4 +44,33 @@
   // but every way to prevent that from hiding the popover also throws an
   // exception, so the return value is not testable.
 }, `togglePopover's return value should reflect what the end state is, not just the force parameter.`);
+
+test(() => {
+  const popover = document.createElement('div');
+  document.body.appendChild(popover);
+
+  assert_throws_dom('NotSupportedError', () => popover.togglePopover(),
+    'togglePopover() should throw an exception when the element has no popover attribute.');
+  assert_throws_dom('NotSupportedError', () => popover.togglePopover(true),
+    'togglePopover(true) should throw an exception when the element has no popover attribute.');
+  assert_throws_dom('NotSupportedError', () => popover.togglePopover(false),
+    'togglePopover(false) should throw an exception when the element has no popover attribute.');
+
+  popover.setAttribute('popover', 'auto');
+  popover.remove();
+
+  assert_throws_dom('InvalidStateError', () => popover.togglePopover(),
+    'togglePopover() should throw an exception when the element is disconnected.');
+  assert_throws_dom('InvalidStateError', () => popover.togglePopover(true),
+    'togglePopover(true) should throw an exception when the element is disconnected.');
+  assert_throws_dom('InvalidStateError', () => popover.togglePopover(false),
+    'togglePopover(false) should throw an exception when the element is disconnected.');
+
+  document.body.appendChild(popover);
+  // togglePopover(false) should not throw just because the popover is already hidden.
+  popover.togglePopover(false);
+  popover.showPopover();
+  // togglePopover(true) should not throw just because the popover is already showing.
+  popover.togglePopover(true);
+}, 'togglePopover should throw an exception when there is no popover attribute.');
 </script>