raise stylesheet error

src/textual/app.py

@@ -2387,7 +2387,7 @@ def _handle_exception(self, error: Exception) -> None:
         self._return_code = 1
         # If we're running via pilot and this is the first exception encountered,
         # take note of it so that we can re-raise for test frameworks later.
-        if self.is_headless and self._exception is None:
+        if self._exception is None:
             self._exception = error
             self._exception_event.set()
 

tests/test_pilot.py

@@ -6,6 +6,7 @@
 from textual.app import App, ComposeResult
 from textual.binding import Binding
 from textual.containers import Center, Middle
+from textual.css.errors import StylesheetError
 from textual.pilot import OutOfBounds
 from textual.screen import Screen
 from textual.widgets import Button, Label
@@ -395,3 +396,14 @@ async def test_pilot_resize_terminal():
         await pilot.pause()
         assert app.size == (27, 15)
         assert app.screen.size == (27, 15)
+
+
+async def test_fail_early():
+    # https://github.com/Textualize/textual/issues/3282
+    class MyApp(App):
+        CSS_PATH = "foo.tcss"
+
+    app = MyApp()
+    with pytest.raises(StylesheetError):
+        async with app.run_test() as pilot:
+            await pilot.press("enter")