check comments early

Author: mgeplf

tests/sample_header_test.py

@@ -7,7 +7,11 @@
 
 
 def test_generate_headers(capsys, tmp_path):
-    comments = pybind11_mkdoc.mkdoc_lib.extract_all([os.path.join(DIR, "sample_header_docs", "sample_header.h")])
+    comments = pybind11_mkdoc.mkdoc_lib.extract_all(
+        [os.path.join(DIR, "sample_header_docs", "sample_header.h")]
+    )
+    assert ['mkd_doc_RootLevelSymbol', 'mkd_doc_drake_MidLevelSymbol'] == [c[0] for c in comments]
+
     output = tmp_path / "docs.h"
     with output.open("w") as fd:
         pybind11_mkdoc.mkdoc_lib.write_header(comments, fd)