test: update app tests for symmetric dropdowns and swap button

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_app.py

@@ -88,31 +88,33 @@ def test_demo_has_no_sliders(demo):
     assert len(sliders) == 0, f"Expected no sliders, found {len(sliders)}"
 
 
-def test_demo_has_english_dropdown(demo):
-    """UI should have a non-interactive English dropdown."""
+def test_demo_has_two_interactive_dropdowns(demo):
+    """UI should have two interactive language dropdowns."""
     dropdowns = [b for b in demo.blocks.values() if type(b).__name__ == "Dropdown"]
-    english = [d for d in dropdowns if d.interactive is False and d.value == "English"]
-    assert len(english) == 1, "Expected exactly one non-interactive English dropdown"
+    assert len(dropdowns) == 2, f"Expected 2 dropdowns, found {len(dropdowns)}"
+    interactive = [d for d in dropdowns if d.interactive is not False]
+    assert len(interactive) == 2, f"Expected 2 interactive dropdowns, found {len(interactive)}"
 
 
-def test_demo_has_dropdown(demo):
-    """UI should have two dropdowns (English + target language)."""
+def test_source_dropdown_default_is_english(demo):
+    """Source dropdown should default to English (en)."""
     dropdowns = [b for b in demo.blocks.values() if type(b).__name__ == "Dropdown"]
-    assert len(dropdowns) == 2, f"Expected 2 dropdowns, found {len(dropdowns)}"
+    english = [d for d in dropdowns if d.value == "English (en)"]
+    assert len(english) == 1, "Expected one dropdown defaulting to 'English (en)'"
 
 
-def test_dropdown_default_is_french(demo):
-    """Default dropdown value should be French (fr)."""
+def test_target_dropdown_default_is_french(demo):
+    """Target dropdown should default to French (fr)."""
     dropdowns = [b for b in demo.blocks.values() if type(b).__name__ == "Dropdown"]
-    interactive = [d for d in dropdowns if d.interactive is not False]
-    assert interactive[0].value == "French (fr)"
+    french = [d for d in dropdowns if d.value == "French (fr)"]
+    assert len(french) == 1, "Expected one dropdown defaulting to 'French (fr)'"
 
 
-def test_dropdown_is_filterable(demo):
-    """Dropdown should be filterable/searchable."""
+def test_both_dropdowns_filterable(demo):
+    """Both language dropdowns should be filterable/searchable."""
     dropdowns = [b for b in demo.blocks.values() if type(b).__name__ == "Dropdown"]
     interactive = [d for d in dropdowns if d.interactive is not False]
-    assert interactive[0].filterable is True
+    assert all(d.filterable is True for d in interactive), "Both dropdowns should be filterable"
 
 
 def test_dropdown_choices_include_locale_codes(demo):
@@ -194,12 +196,28 @@ def test_demo_has_no_html_elements(demo):
     assert len(html_blocks) == 0, f"Expected no HTML blocks, found {len(html_blocks)}"
 
 
+def test_demo_has_swap_button(demo):
+    """UI should have a swap button."""
+    buttons = [b for b in demo.blocks.values() if type(b).__name__ == "Button"]
+    swap = [b for b in buttons if "⇄" in str(b.value)]
+    assert len(swap) == 1, "Expected one swap button"
+
+
+def test_swap_handler_wired(demo):
+    """Swap button should have a click handler with 4 inputs and 4 outputs."""
+    swap_fns = [fn for fn in demo.fns.values() if len(fn.inputs) == 4 and len(fn.outputs) == 4]
+    assert len(swap_fns) >= 1, "Expected a handler with 4 inputs and 4 outputs (swap handler)"
+
+
 def test_translate_handlers_wire_text_and_language(demo):
     """Translate click and submit handlers should wire input text and target language."""
     translate_fns = [fn for fn in demo.fns.values() if [type(i).__name__ for i in fn.inputs] == ["Textbox", "Dropdown"]]
     assert len(translate_fns) == 2, f"Expected 2 translate handlers (click + submit), found {len(translate_fns)}"
 
 
+def test_all_handlers_wired(demo):
+    """UI should have exactly 3 click/submit handlers: translate click, translate submit, swap."""
+    assert len(demo.fns) == 3, f"Expected 3 handlers, found {len(demo.fns)}"
 
 
 def test_no_title(demo):