Enhance SegmentedButton icon support and tests

Updated SegmentedButton to support both IconData and Control for selected_icon. Improved integration tests for segmented button, added golden images for macOS, and documented SegmentedButtonTheme options. Also clarified NavigationBarTheme test comments.

Author: InesaFitsner

packages/flet/lib/src/controls/segmented_button.dart

@@ -84,7 +84,7 @@ class _SegmentedButtonControlState extends State<SegmentedButtonControl>
         selected: selected,
         showSelectedIcon: widget.control.getBool("show_selected_icon", true)!,
         style: style,
-        selectedIcon: widget.control.buildWidget("selected_icon"),
+        selectedIcon: widget.control.buildIconOrWidget("selected_icon"),
         onSelectionChanged: !widget.control.disabled
             ? (newSelection) => onChange(newSelection)
             : null,

sdk/python/packages/flet/integration_tests/controls/golden/macos/segmented_button/basic.png

@@ -34,8 +34,8 @@ async def test_theme(flet_app: ftt.FletTestApp):
     flet_app.page.theme = ft.Theme(
         navigation_bar_theme=ft.NavigationBarTheme(
             bgcolor=ft.Colors.GREEN_200,
-            shadow_color=ft.Colors.ORANGE_500,
-            elevation=50,
+            shadow_color=ft.Colors.ORANGE_500,  # not shows in the screenshot
+            elevation=50,  # not shows in the screenshot
             indicator_color=ft.Colors.GREEN,
             overlay_color=ft.Colors.YELLOW_300,
             height=200,

sdk/python/packages/flet/integration_tests/controls/golden/macos/segmented_button/theme_1.png

@@ -1,23 +1,27 @@
 import pytest
+import pytest_asyncio
 
 import flet as ft
 import flet.testing as ftt
 
 
-@pytest.mark.asyncio(loop_scope="module")
-async def test_segmented_button_basic(flet_app: ftt.FletTestApp, request):
+# Create a new flet_app instance for each test method
+@pytest_asyncio.fixture(scope="function", autouse=True)
+def flet_app(flet_app_function):
+    return flet_app_function
+
+
+@pytest.mark.asyncio(loop_scope="function")
+async def test_basic(flet_app: ftt.FletTestApp, request):
     await flet_app.assert_control_screenshot(
         request.node.name,
         ft.SegmentedButton(
-            selected_icon=ft.Icon(ft.Icons.CHECK_SHARP),
             selected=["1"],
-            allow_empty_selection=True,
-            allow_multiple_selection=True,
             segments=[
                 ft.Segment(
                     value="1",
-                    label=ft.Text("1"),
-                    icon=ft.Icon(ft.Icons.LOOKS_ONE),
+                    label="1",
+                    icon=ft.Icons.LOOKS_ONE,
                 ),
                 ft.Segment(
                     value="2",
@@ -27,13 +31,61 @@ async def test_segmented_button_basic(flet_app: ftt.FletTestApp, request):
                 ft.Segment(
                     value="3",
                     label=ft.Text("3"),
-                    icon=ft.Icon(ft.Icons.LOOKS_3),
                 ),
                 ft.Segment(
                     value="4",
-                    label=ft.Text("4"),
-                    icon=ft.Icon(ft.Icons.LOOKS_4),
+                    icon=ft.Icons.LOOKS_4,
                 ),
             ],
         ),
     )
+
+
+@pytest.mark.asyncio(loop_scope="function")
+async def test_theme(flet_app: ftt.FletTestApp):
+    flet_app.page.theme = ft.Theme(
+        segmented_button_theme=ft.SegmentedButtonTheme(
+            selected_icon=ft.Icons.HOME,
+            style=ft.ButtonStyle(
+                bgcolor=ft.Colors.BLUE, shape=ft.BeveledRectangleBorder()
+            ),
+        )
+    )
+    flet_app.page.enable_screenshots = True
+    flet_app.page.window.width = 400
+    flet_app.page.window.height = 600
+
+    scr_1 = ft.Screenshot(
+        ft.SegmentedButton(
+            selected=["1"],
+            segments=[
+                ft.Segment(
+                    value="1",
+                    label="1",
+                    icon=ft.Icons.LOOKS_ONE,
+                ),
+                ft.Segment(
+                    value="2",
+                    label=ft.Text("2"),
+                    icon=ft.Icon(ft.Icons.LOOKS_TWO),
+                ),
+                ft.Segment(
+                    value="3",
+                    label=ft.Text("3"),
+                ),
+                ft.Segment(
+                    value="4",
+                    icon=ft.Icons.LOOKS_4,
+                ),
+            ],
+        ),
+        key="sb",
+    )
+    flet_app.page.add(scr_1)
+    flet_app.page.update()
+    await flet_app.tester.pump_and_settle()
+
+    flet_app.assert_screenshot(
+        "theme_1",
+        await scr_1.capture(pixel_ratio=flet_app.screenshots_pixel_ratio),
+    )

sdk/python/packages/flet/integration_tests/controls/test_navigation_bar.py

@@ -105,7 +105,7 @@ class SegmentedButton(ConstrainedControl):
     when the user (un)selects a segment.
     """
 
-    selected_icon: Optional[Control] = None
+    selected_icon: Optional[IconDataOrControl] = None
     """
     An `Icon` control that is used to indicate a segment is selected.
 

sdk/python/packages/flet/integration_tests/controls/test_segmented_button.py

@@ -3152,8 +3152,22 @@ class NavigationBarTheme:
 
 @dataclass
 class SegmentedButtonTheme:
+    """
+    Customizes the appearance of descendant [`SegmentedButton`][flet.SegmentedButton]
+    controls.
+    """
+
     selected_icon: Optional[IconData] = None
+    """
+    Overrides the default value for
+    [`SegmentedButton.selected_icon`][flet.SegmentedButton.selected_icon].
+    """
+
     style: Optional[ButtonStyle] = None
+    """
+    Overrides the default value for
+    [`SegmentedButton.style`][flet.SegmentedButton.style].
+    """
 
 
 @dataclass