Fix slug lookup and add regression test

tests/test_apothecary_page.py

@@ -0,0 +1,27 @@
+import urllib.error
+import urllib.request
+import unittest
+
+URL = 'https://howdoyouconvert.com/apothecary-ounces-to-amu'
+
+
+class ApothecaryPageTests(unittest.TestCase):
+    def test_apothecary_page_returns_success(self) -> None:
+        """The published URL should return a 200 so the calculator page stays healthy."""
+        request = urllib.request.Request(
+            URL,
+            headers={
+                'User-Agent': 'Mozilla/5.0',
+                'Accept': 'text/html,application/xhtml+xml',
+            },
+        )
+
+        try:
+            with urllib.request.urlopen(request, timeout=15) as response:
+                status = response.getcode()
+        except urllib.error.HTTPError as exc:
+            self.fail(f'{URL} returned HTTP {exc.code} ({exc.reason})')
+        except urllib.error.URLError as exc:
+            self.fail(f'{URL} could not be fetched: {exc}')
+
+        self.assertEqual(status, 200, f'{URL} returned {status}')