Add missing test

Author: agg23

tests/async/test_selectors_misc.py

@@ -12,6 +12,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import pytest
+
+from playwright._impl._errors import Error
+from playwright._impl._selectors import Selectors
 from playwright.async_api import Page
 
 
@@ -52,3 +56,14 @@ async def test_should_work_with_internal_and(page: Page) -> None:
             '.bar >> internal:and="span"', "els => els.map(e => e.textContent)"
         )
     ) == ["world2"]
+
+
+async def test_should_throw_already_registered_error_when_registering(
+    selectors: Selectors,
+) -> None:
+    await selectors.register("alreadyRegistered", "return []")
+    with pytest.raises(
+        Error,
+        match='Selectors.register: "alreadyRegistered" selector engine has been already registered',
+    ):
+        await selectors.register("alreadyRegistered", "return []")