Add a test for Textualize#4301

tests/text_area/test_issue_4301.py

@@ -0,0 +1,28 @@
+from textual.app import App, ComposeResult
+from textual.widgets import TextArea
+from textual.widgets.text_area import Selection
+
+TEST_TEXT = "\n".join(f"01234567890 - {n}" for n in range(10))
+TEST_SELECTION = Selection((2, 5), (0, 5))
+TEST_SELECTED_TEXT = "567890 - 0\n01234567890 - 1\n01234"
+TEST_REPLACEMENT = "A"
+TEST_RESULT_TEXT = TEST_TEXT.replace(TEST_SELECTED_TEXT, TEST_REPLACEMENT)
+
+
+class TextAreaApp(App[None]):
+
+    def compose(self) -> ComposeResult:
+        yield TextArea(TEST_TEXT)
+
+
+async def test_issue_4301_reproduction() -> None:
+
+    async with (app := TextAreaApp()).run_test() as pilot:
+        assert app.query_one(TextArea).text == TEST_TEXT
+        app.query_one(TextArea).selection = TEST_SELECTION
+        assert app.query_one(TextArea).selected_text == TEST_SELECTED_TEXT
+        await pilot.press("A")
+        assert app.query_one(TextArea).text == TEST_RESULT_TEXT
+        await pilot.press("ctrl+z")
+        assert app.query_one(TextArea).text == TEST_TEXT
+        await pilot.press(*(["down"] * 10))