Polish commands and cover them with tests

Author: johnslavik

Lib/_pyrepl/commands.py

@@ -469,15 +469,13 @@ def do(self) -> None:
 
 class invalid_key(Command):
     def do(self) -> None:
-        pending = self.reader.console.getpending()
-        s = "".join(self.event) + pending.data
-        self.reader.error("`%r' not bound" % s)
+        self.reader.console.getpending()
+        self.reader.error("no command is bound to this key")
 
 
 class invalid_command(Command):
     def do(self) -> None:
-        s = self.event_name
-        self.reader.error("command `%s' not known" % s)
+        self.reader.error(f"command {self.event_name!r} is not implemented")
 
 
 class show_history(Command):

Lib/test/test_pyrepl/test_reader.py

@@ -456,6 +456,47 @@ def test_setpos_from_xy_for_non_printing_char(self):
         reader.setpos_from_xy(8, 0)
         self.assertEqual(reader.pos, 7)
 
+
+@force_not_colorized_test_class
+class TestErrorMessages(TestCase):
+    def _test_error_message(
+        self,
+        keys: str,
+        expected: str, *,
+        command: str | None = None,
+    ):
+        console = prepare_console(code_to_events(keys))
+        reader = prepare_reader(console)
+        if command is not None:
+            reader.bind(keys, command)
+
+        while not reader.msg:
+            reader.handle1()
+
+        self.assertEqual(reader.msg, f"! {expected}")
+        self.assertEqual(reader.screen[-1], f"! {expected}")
+        console.beep.assert_called_once()
+
+    def test_invalid_key_message(self):
+        self._test_error_message("\x1bo", "no command is bound to this key")
+
+    def test_unimplemented_command_message(self):
+        self._test_error_message(
+            "x",
+            "command 'missing-command' is not implemented",
+            command="missing-command",
+        )
+
+    def test_nothing_to_yank_message(self):
+        self._test_error_message("\x19", "nothing to yank")
+
+    def test_start_of_history_message(self):
+        self._test_error_message("\x10", "start of history list")
+
+    def test_no_completion_matches_message(self):
+        self._test_error_message("does_not_exist\t", "no matches")
+
+
 @force_colorized_test_class
 class TestReaderInColor(ScreenEqualMixin, TestCase):
     def test_syntax_highlighting_basic(self):