Add comprehensive unit tests for core functions

Added 62 unit tests (441 lines) covering high-priority functions:
- test_parse_headers.py: 9 tests for header parsing logic
- test_render.py: 15 tests for template engine
- test_strip_html_tags.py: 18 tests for HTML tag removal
- test_strip_tags_and_truncate.py: 19 tests for summary generation

All tests pass and cover edge cases, error conditions, and real-world scenarios.

test/test_parse_headers.py

@@ -0,0 +1,83 @@
+import unittest
+import makesite
+
+
+class ParseHeadersTest(unittest.TestCase):
+
+    def test_single_header(self):
+        """Test parsing a single header."""
+        text = "<!-- title: My Post Title -->\nContent here"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 1)
+        self.assertEqual(headers[0][0], "title")
+        self.assertEqual(headers[0][1], "My Post Title")
+
+    def test_multiple_headers(self):
+        """Test parsing multiple headers."""
+        text = """<!-- title: My Post -->
+<!-- category: Tech Python -->
+<!-- tag: blog tutorial -->
+Content starts here"""
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 3)
+        self.assertEqual(headers[0], ("title", "My Post", headers[0][2]))
+        self.assertEqual(headers[1], ("category", "Tech Python", headers[1][2]))
+        self.assertEqual(headers[2], ("tag", "blog tutorial", headers[2][2]))
+
+    def test_headers_with_extra_whitespace(self):
+        """Test parsing headers with extra whitespace."""
+        text = "<!--   title  :  My Post  -->\n<!-- category:Tech-->\nContent"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 2)
+        self.assertEqual(headers[0][0], "title")
+        self.assertEqual(headers[0][1], "My Post")
+        self.assertEqual(headers[1][0], "category")
+        self.assertEqual(headers[1][1], "Tech")
+
+    def test_no_headers(self):
+        """Test parsing content with no headers."""
+        text = "Just regular content\nNo headers here"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 0)
+
+    def test_headers_stop_at_content(self):
+        """Test that parsing stops when content (non-header) is found."""
+        text = """<!-- title: Post Title -->
+<!-- category: Tech -->
+This is content
+<!-- tag: not-a-header -->"""
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 2)
+        # Should only get title and category, not the tag after content
+
+    def test_header_with_special_characters(self):
+        """Test parsing headers with special characters in values."""
+        text = "<!-- title: C'est l'été! Les accents: àéêô -->\nContent"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 1)
+        self.assertEqual(headers[0][1], "C'est l'été! Les accents: àéêô")
+
+    def test_header_with_colon_in_value(self):
+        """Test parsing headers where the value contains colons."""
+        text = "<!-- title: Docker: Configuration et Sécurité -->\nContent"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 1)
+        self.assertEqual(headers[0][1], "Docker: Configuration et Sécurité")
+
+    def test_empty_header_value(self):
+        """Test parsing headers with empty values."""
+        text = "<!-- title: -->\n<!-- category: Tech -->\nContent"
+        headers = list(makesite._parse_headers(text))
+        self.assertEqual(len(headers), 2)
+        # Empty value results in a single space due to regex whitespace handling
+        self.assertEqual(headers[0][1].strip(), "")
+        self.assertEqual(headers[1][1], "Tech")
+
+    def test_end_index_tracking(self):
+        """Test that end index correctly tracks position after headers."""
+        text = "<!-- title: Test -->\n<!-- tag: python -->\nContent starts"
+        headers = list(makesite._parse_headers(text))
+        # The last header's end index should point to where content starts
+        last_end = headers[-1][2]
+        self.assertTrue(last_end > 0)
+        self.assertTrue(text[last_end:].startswith("Content") or text[last_end:].startswith("\nContent"))