diff --git a/changedetectionio/tests/unit/test_content_type_detection.py b/changedetectionio/tests/unit/test_content_type_detection.py
new file mode 100644
index 00000000..e5746bb0
--- /dev/null
+++ b/changedetectionio/tests/unit/test_content_type_detection.py
@@ -0,0 +1,131 @@
+#!/usr/bin/env python3
+# coding=utf-8
+
+# run from dir above changedetectionio/ dir
+# python3 -m unittest changedetectionio.tests.unit.test_content_type_detection
+
+"""Unit tests for guess_stream_type() content-type classification.
+
+Regression cover for #4302: a normal HTML page served as 'text/html;charset=utf-8' was
+classified as plaintext, which made processor.py skip html_to_text() entirely and store the
+raw filtered block as the snapshot (visible as literal '
' separators in every diff).
+
+Two independent failures had to line up:
+ 1. The header test was an exact comparison ("text/html"), so any charset parameter missed it.
+ 2. has_html_patterns only sniffs content[:200], and the page put 241 bytes of HTML comments
+ before is_plaintext.
+"""
+
+import unittest
+
+from changedetectionio.processors.magic import guess_stream_type
+
+# Real-world shape from https://www.newbalancemexico.com/c/lo-mas-nuevo (Salesforce/ISML templates):
+# blank lines and two long comments push \n"
+ "\n\n\n"
+ '\n\n\n\n\n'
+ ''
+)
+
+PLAIN_HTML = 'thi
'
+
+
+class TestGuessStreamType(unittest.TestCase):
+
+ def _flags(self, header, content):
+ st = guess_stream_type(http_content_header=header, content=content)
+ return {n: getattr(st, n) for n in
+ ('is_html', 'is_plaintext', 'is_rss', 'is_xml', 'is_json', 'is_pdf', 'is_csv')}
+
+ def test_preamble_pushes_doctype_past_sniff_window(self):
+ # Guard the premise of the test below - if this ever shrinks, the regression case is no
+ # longer exercising the "content sniff cannot help" path.
+ self.assertGreater(COMMENT_PREAMBLE_HTML.index('\nf'
+ atom = '\nf'
+ json_doc = '{"title": "hello", "items": [1, 2, 3]}'
+
+ self.assertTrue(self._flags('text/html;charset=utf-8', rss)['is_rss'])
+ self.assertTrue(self._flags('text/html;charset=utf-8', atom)['is_rss'])
+ self.assertTrue(self._flags('application/json', json_doc)['is_json'])
+ self.assertTrue(self._flags('text/xml', 'x')['is_xml'])
+
+
+class TestFilterSeparatorSurvivesTextExtraction(unittest.TestCase):
+ """#4302 end to end: an attribute xpath must produce newlines, never a literal '
'.
+
+ xpath_filter injects TEXT_FILTER_LIST_LINE_SUFFIX ('
') between matches that have no
+ .tag attribute - i.e. attribute and text() nodes, which is precisely when the filter output
+ is no longer HTML. That marker is only removed if html_to_text() runs, so this test pins the
+ classification and the conversion together.
+ """
+
+ def test_attribute_xpath_matches_become_newlines(self):
+ from changedetectionio import html_tools
+
+ filtered = html_tools.xpath_filter(
+ xpath_filter='//div[@class="product"]/@data-pid',
+ html_content=COMMENT_PREAMBLE_HTML.replace(
+ '',
+ ''
+ ''),
+ append_pretty_line_formatting=True,
+ )
+ # The marker is expected at this stage - it is an intermediate value, not a snapshot.
+ self.assertIn('
', filtered)
+
+ stream = guess_stream_type(http_content_header='text/html;charset=utf-8',
+ content=COMMENT_PREAMBLE_HTML)
+ self.assertTrue(stream.is_html)
+ self.assertFalse(stream.is_plaintext)
+
+ text = html_tools.html_to_text(html_content=filtered, is_rss=stream.is_rss)
+ self.assertNotIn('
', text, "'
' leaked into the snapshot - see #4302")
+ self.assertIn('U204LMMA', text)
+ self.assertIn('MR530KA', text)
+ self.assertEqual(['U204LMMA', 'MR530KA'], text.split())
+
+
+if __name__ == '__main__':
+ # Can run this file directly for quick testing
+ unittest.main()