Fix bad return bug

Previously (due to a hangover from an earlier implementation), if we
were missing a name or title from the code block, we would return _only_
the `example_cell` in question, not the whole `chapter`. This was
causing a few odd bugs but now has been fixed, and I've added a test to
guard against this in the future.

Author: delfanbaum

jupyter_book_to_htmlbook/code_processing.py

@@ -138,7 +138,7 @@ def process_code_examples(chapter):
             logging.warning(
                 "Missing first two line comments for uuid and title." +
                 f"Unable to apply example formatting to {example_cell}.")
-            return example_cell
+            return chapter
 
         # ensure comments are within the first three spans (since we
         # expect an empty span to start based on their highlighter)

tests/test_code_processing.py

@@ -405,6 +405,29 @@ def test_malformed_example_missing_title(self, caplog):
         assert "Unable to apply example formatting" in log
         assert not result.find("div", class_="highlight").get("data-type")
 
+    def test_malformed_example_does_not_destroy_chapter(self, caplog):
+        """
+        Once we had a bad return given failures; this test is to
+        ensure that even if we don't add example formatting, we also
+        do not only return the bad block.
+        """
+        expect_fail = BeautifulSoup("""
+<div id="do_not_lose_me">Hello!</div>
+<div class="cell tag_example docutils container">
+<div class="cell_input docutils container">
+<div class="highlight-ipython3 notranslate"><div class="highlight">
+<pre><span></span><span class="c1"># This is an example title</span>
+
+<span class="k">def</span> <span class="nf">h</span><span class="p">():</span>
+    <span class="k">pass</span></pre></div></div></div></div>
+""", "html.parser")
+        caplog.set_level(logging.DEBUG)
+        result = process_code_examples(expect_fail)
+        log = caplog.text
+        assert "Unable to apply example formatting" in log
+        assert not result.find("div", class_="highlight").get("data-type")
+        assert result.find("div", id="do_not_lose_me")
+
     def test_malformed_example_with_extra_comments_later(self, caplog):
         """
         Ensure that we're logging failures (e.g., when an author doesn't