1 files changed, 29 insertions, 0 deletions
diff --git a/bs4/tests/test_builder.py b/bs4/tests/test_builder.py
new file mode 100644
index 0000000..7537071
--- /dev/null
+++ b/bs4/tests/test_builder.py
@@ -0,0 +1,29 @@
+import pytest
+from unittest.mock import patch
+from bs4.builder import DetectsXMLParsedAsHTML
+
+class TestDetectsXMLParsedAsHTML(object):
+
+    @pytest.mark.parametrize(
+        "markup,looks_like_xml",
+        [("No xml declaration", False),
+         ("<html>obviously HTML</html", False),
+         ("<?xml ><html>Actually XHTML</html>", False),
+         ("<?xml>            <    html>Tricky XHTML</html>", False),
+         ("<?xml ><no-html-tag>", True),
+        ]
+    )
+    def test_warn_if_markup_looks_like_xml(self, markup, looks_like_xml):
+        # Test of our ability to guess at whether markup looks XML-ish
+        # _and_ not HTML-ish.
+        with patch('bs4.builder.DetectsXMLParsedAsHTML._warn') as mock:
+            for data in markup, markup.encode('utf8'):
+                result = DetectsXMLParsedAsHTML.warn_if_markup_looks_like_xml(
+                    data
+                )
+                assert result == looks_like_xml
+                if looks_like_xml:
+                    assert mock.called
+                else:
+                    assert not mock.called
+                mock.reset_mock()