Fix bilingual tutorial indexes and internal links (#209)

* Fix bilingual tutorial index generation

* Check relative Markdown links in CI

* Harden documentation regression checks

* Reduce link parser complexity

* Run link checks for every repository change

---------

Co-authored-by: LinuxDev9002 <i@littlefisher.me>

scripts/test_generate_toc.py

@@ -0,0 +1,49 @@
+import re
+import unittest
+from pathlib import Path
+
+from scripts.generate_toc import generate_toc, generate_toc_cn
+
+
+ROOT = Path(__file__).resolve().parent.parent
+LINK_PATTERN = re.compile(r"\]\((src/.+?)/README(?:\.zh)?\.md\)")
+TRACING_LESSONS = {
+    "src/30-sslsniff",
+    "src/31-goroutine",
+    "src/33-funclatency",
+    "src/37-uprobe-rust",
+    "src/39-nginx",
+    "src/40-mysql",
+    "src/48-energy",
+}
+
+
+def lesson_links(markdown: str) -> set[str]:
+    return set(LINK_PATTERN.findall(markdown))
+
+
+def subsection(markdown: str, heading: str, next_heading: str) -> str:
+    return markdown.split(f"\n\n{heading}:\n\n", 1)[1].split(
+        f"\n\n{next_heading}:\n\n", 1
+    )[0]
+
+
+class TocParityTest(unittest.TestCase):
+    @classmethod
+    def setUpClass(cls):
+        cls.english = generate_toc(ROOT / "src", ROOT, ROOT)
+        cls.chinese = generate_toc_cn(ROOT / "src", ROOT, ROOT)
+
+    def test_english_and_chinese_indexes_contain_the_same_lessons(self):
+        self.assertSetEqual(lesson_links(self.english), lesson_links(self.chinese))
+
+    def test_chinese_tracing_subsection_contains_all_tracing_lessons(self):
+        english_tracing = lesson_links(subsection(self.english, "Tracing", "Security"))
+        chinese_tracing = lesson_links(subsection(self.chinese, "追踪", "安全"))
+
+        self.assertSetEqual(english_tracing, TRACING_LESSONS)
+        self.assertSetEqual(chinese_tracing, TRACING_LESSONS)
+
+
+if __name__ == "__main__":
+    unittest.main()