Fix select value being reset when toggling popup via User fixture (#5670)

### Motivation

Fixes #4894

When using the `User` fixture to test select elements, clicking a select
found by its label (e.g., `user.find('Fruit').click()`) to toggle the
popup would incorrectly reset the select's value to `None`.

The bug occurred because the click handler used `self.target` (which was
the label like `'Fruit'`) as the value to set. Since the label is not a
valid option in the select's options list, this triggered validation
that set the value to `None`.

### Implementation

Before setting the value, the code now checks if `self.target` is
actually a valid option:
- For list options: checks if `self.target in element._values`
- For dict options: checks if any option label matches `self.target`

If the target is not a valid option (meaning the user clicked the select
itself, not an option), the code just toggles the popup state without
modifying the value.

### Progress

- [x] I chose a meaningful title that completes the sentence: "If
applied, this PR will..."
- [x] The implementation is complete.
- [x] This is not a security issue.
- [x] Pytests have been added.
- [x] Documentation is not necessary.

Author: falkoschindler

nicegui/testing/user_interaction.py

@@ -72,7 +72,7 @@ def click(self) -> Self:
         """Click the selected elements."""
         assert self.user.client
         with self.user.client:
-            for element in self.elements:
+            for element in self.elements:  # pylint: disable=too-many-nested-blocks
                 if isinstance(element, DisableableElement) and not element.enabled:
                     continue
                 if isinstance(element, ui.link):
@@ -83,18 +83,21 @@ def click(self) -> Self:
                 if isinstance(element, ui.select):
                     if element.is_showing_popup:
                         if isinstance(element.options, dict):
-                            target_value = next((k for k, v in element.options.items() if v == self.target), '')
+                            target_value = next((k for k, v in element.options.items() if v == self.target), None)
                         else:
-                            target_value = self.target
-                        if element.multiple:
-                            if target_value in element.value:
-                                element.value = [v for v in element.value if v != target_value]
-                            elif target_value in element._values:  # pylint: disable=protected-access
-                                element.value = [*element.value, target_value]
+                            target_value = self.target if self.target in element._values else None  # pylint: disable=protected-access
+                        if target_value is not None:
+                            # User clicked on a valid option: update the value and close the popup
+                            if element.multiple:
+                                if target_value in element.value:
+                                    element.value = [v for v in element.value if v != target_value]
+                                else:
+                                    element.value = [*element.value, target_value]
                             else:
+                                element.value = target_value
                                 element._is_showing_popup = False  # pylint: disable=protected-access
                         else:
-                            element.value = target_value
+                            # User clicked the select itself (not a valid option): just close the popup
                             element._is_showing_popup = False  # pylint: disable=protected-access
                     else:
                         element._is_showing_popup = True  # pylint: disable=protected-access

tests/test_user_simulation.py

@@ -511,6 +511,27 @@ def page():
     assert select.value == ['B']
 
 
+async def test_select_keeps_value_when_toggling_popup(user: User):
+    @ui.page('/')
+    def page():
+        s = ui.select(['Apple', 'Banana', 'Cherry'], label='Fruit', value='Apple')
+        ui.label().bind_text_from(s, 'is_showing_popup', lambda v: 'open' if v else 'closed')
+        ui.label().bind_text_from(s, 'value', lambda v: f'value = {v}')
+
+    await user.open('/')
+    one = user.find('Fruit')
+    await user.should_see('closed')
+    await user.should_see('value = Apple')
+
+    one.click()
+    await user.should_see('open')
+    await user.should_see('value = Apple')
+
+    one.click()
+    await user.should_see('closed')
+    await user.should_see('value = Apple')
+
+
 async def test_upload_table(user: User) -> None:
     @ui.page('/')
     def page():