Make the naked invocation display a compacted help

tests/test_cli_ui.py

@@ -0,0 +1,84 @@
+import pytest
+import shutil
+import os
+import sys
+from tests.utils import http
+
+
+if sys.version_info >= (3, 9):
+    REQUEST_ITEM_MSG = "[REQUEST_ITEM ...]"
+else:
+    REQUEST_ITEM_MSG = "[REQUEST_ITEM [REQUEST_ITEM ...]]"
+
+
+NAKED_HELP_MESSAGE = f"""\
+usage:
+    http [METHOD] URL {REQUEST_ITEM_MSG}
+
+error:
+    the following arguments are required: URL
+
+For more information:
+    - Try running http --help
+    - Or visiting https://httpie.io/docs/cli
+
+"""
+
+NAKED_HELP_MESSAGE_PRETTY_WITH_NO_ARG = f"""\
+usage:
+    http [--pretty {{all,colors,format,none}}] [METHOD] URL {REQUEST_ITEM_MSG}
+
+error:
+    argument --pretty: expected one argument
+
+For more information:
+    - Try running http --help
+    - Or visiting https://httpie.io/docs/cli
+
+"""
+
+NAKED_HELP_MESSAGE_PRETTY_WITH_INVALID_ARG = f"""\
+usage:
+    http [--pretty {{all,colors,format,none}}] [METHOD] URL {REQUEST_ITEM_MSG}
+
+error:
+    argument --pretty: invalid choice: '$invalid' (choose from 'all', 'colors', 'format', 'none')
+
+For more information:
+    - Try running http --help
+    - Or visiting https://httpie.io/docs/cli
+
+"""
+
+
+PREDEFINED_TERMINAL_SIZE = (160, 80)
+
+
+@pytest.fixture(scope="function")
+def ignore_terminal_size(monkeypatch):
+    """Some tests wrap/crop the output depending on the
+    size of the executed terminal, which might not be consistent
+    through all runs.
+
+    This fixture ensures every run uses the same exact configuration.
+    """
+
+    def fake_terminal_size(*args, **kwargs):
+        return os.terminal_size(PREDEFINED_TERMINAL_SIZE)
+
+    # Setting COLUMNS as an env var is required for 3.8<
+    monkeypatch.setitem(os.environ, 'COLUMNS', str(PREDEFINED_TERMINAL_SIZE[0]))
+    monkeypatch.setattr(shutil, 'get_terminal_size', fake_terminal_size)
+
+
+@pytest.mark.parametrize(
+    'args, expected_msg', [
+        ([], NAKED_HELP_MESSAGE),
+        (['--pretty'], NAKED_HELP_MESSAGE_PRETTY_WITH_NO_ARG),
+        (['pie.dev', '--pretty'], NAKED_HELP_MESSAGE_PRETTY_WITH_NO_ARG),
+        (['--pretty', '$invalid'], NAKED_HELP_MESSAGE_PRETTY_WITH_INVALID_ARG),
+    ]
+)
+def test_naked_invocation(ignore_terminal_size, args, expected_msg):
+    result = http(*args, tolerate_error_exit_status=True)
+    assert result.stderr == expected_msg