Add tests for vanilla Django RawID fields

Since we overwrite the Django popup lookup JS, we need to make sure we don't break the vanilla experience.

dynamic_raw_id/tests/test_django_admin.py

@@ -0,0 +1,60 @@
+"""
+Test vanilla Django raw id fields since we overwrite it's Javascript
+"""
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+import pytest
+from selenium.webdriver.common.by import By
+
+if TYPE_CHECKING:
+    from selenium.webdriver.firefox.webdriver import WebDriver
+
+
+@pytest.mark.usefixtures("_add_page", "_sample_primary_keys")
+def test_widgets(selenium: WebDriver) -> None:
+    """
+    Test the variations of the Dynamic Raw ID Widget.
+
+    The tests select the "Lookup" icon, choose the first element in the result set,
+    and test that the selected element name appears next to the field.
+
+    Doing this in a all-in-one testcase, rather a parameterized test, so it's much
+    faster.
+    """
+
+    # Input Field ID, Select Value, Test Value
+    tests = (
+        ("rawid_fk", "user1", "user1"),
+        ("rawid_fk_limited", "admin", "admin"),
+        ("rawid_many", "user1", None),
+        ("rawid_many", "user2", None),  # Second click on Many2Many
+    )
+
+    for id_value, select_value, _ in tests:
+        # Select the "Lookup" icon next to the field
+        selenium.find_element(By.ID, f"lookup_id_{id_value}").click()
+
+        #  Activate the popup window with the `window.name = <window_id>`
+        selenium.switch_to.window(selenium.window_handles[1])
+
+        # Select the result element matching the link text
+        selenium.find_element(By.LINK_TEXT, select_value).click()
+
+        # Activate the default window
+        selenium.switch_to.window(selenium.window_handles[0])
+
+    # Click the save button and wait for page reload
+    selenium.find_element(By.NAME, "_continue").click()
+    selenium.implicitly_wait(0.5)  # Wait a bit for page reload
+
+    # Test that all selected ForeignKeys are now displayed after reload.
+    for id_value, _, test_value in tests:
+        # ManyToMany fields don't display a label in Vanilla Django raw id fields.
+        if test_value is None:
+            continue
+
+        label = selenium.find_element(By.CSS_SELECTOR, f"#id_{id_value} ~ strong")
+        assert label.text == test_value