Fix inverted --default-title command-line flag

markdownify/main.py

@@ -26,7 +26,7 @@ def main(argv=sys.argv[1:]):
     parser.add_argument('-a', '--autolinks', action='store_true',
                         help="A boolean indicating whether the 'automatic link' style "
                         "should be used when a 'a' tag's contents match its href.")
-    parser.add_argument('--default-title', action='store_false',
+    parser.add_argument('--default-title', action='store_true',
                         help="A boolean to enable setting the title of a link to its "
                         "href, if no title is given.")
     parser.add_argument('--heading-style', default=UNDERLINED,

tests/test_cli.py

@@ -0,0 +1,18 @@
+from io import StringIO
+
+import pytest
+
+from markdownify.main import main
+
+
+@pytest.mark.parametrize('args, title, expected_title', [
+    ([], '', ''),
+    (['--default-title'], '', ' "https://example.com"'),
+    ([], ' title="Example"', ' "Example"'),
+    (['--default-title'], ' title="Example"', ' "Example"'),
+])
+def test_default_title(args, title, expected_title, monkeypatch, capsys):
+    html = '<a href="https://example.com"%s>Example</a>' % title
+    monkeypatch.setattr('sys.stdin', StringIO(html))
+    main(args)
+    assert capsys.readouterr().out == '[Example](https://example.com%s)\n' % expected_title