Rework '/versions' validator to force check on 'text/csv'

optimade/validator/validator.py

@@ -947,13 +947,17 @@ def _test_versions_endpoint(self):
     @test_case
     def _test_versions_endpoint_content(
         self, response: requests.Response
-    ) -> Tuple[Optional[requests.Response], str]:
+    ) -> Tuple[requests.Response, str]:
         """Checks that the response from the versions endpoint complies
-        with the specification.
+        with the specification and that its 'Content-Type' header complies with
+        [RFC 4180](https://tools.ietf.org/html/rfc4180.html).
 
         Parameters:
             response: The HTTP response from the versions endpoint.
 
+        Raises:
+            ResponseError: If any content checks fail.
+
         Returns:
             The successful HTTP response or `None`, and a summary string.
 
@@ -977,37 +981,48 @@ def _test_versions_endpoint_content(
                     f"Version numbers reported by `/{CONF.versions_endpoint}` must be integers specifying the major version, not {text_content}."
                 )
 
-        self._test_versions_headers(response, optional=True)
+        content_type = response.headers.get("content-type")
+        if not content_type:
+            raise ResponseError(
+                "Missing 'Content-Type' in response header from `/versions`."
+            )
+
+        content_type = [_.replace(" ", "") for _ in content_type.split(";")]
+
+        self._test_versions_headers(content_type, "text/csv")
+        self._test_versions_headers(content_type, "header=present", optional=True)
 
         return response, "`/versions` endpoint responded correctly."
 
     @test_case
     def _test_versions_headers(
-        self, response: requests.Response, optional: bool = True
-    ):
-        """Tests that the versions endpoint responds with the correct optional
-        headers, namely that Content-Type contains both `text/csv` and
-        `headers=present` as per [RFC 4180](https://tools.ietf.org/html/rfc4180.html).
-
+        self, content_type: Dict[str, Any], expected_parameter: str
+    ) -> Tuple[Dict[str, Any], str]:
+        """Tests that the `Content-Type` field of the `/versions` header contains
+        the passed parameter.
 
+        Arguments:
+            content_type: The 'Content-Type' field from the response of the `/versions` endpoint.
+            expected_paramter: A substring that is expected in the Content-Type of the response.
 
-        """
-        content_type = response.headers.get("content-type")
-        if content_type is not None:
-            content_type = [_.replace(" ", "") for _ in content_type.split(";")]
+        Raises:
+            ResponseError: If the expected 'Content-Type' parameter is missing.
 
-        expected_headers = ("text/csv", "header=present")
+        Returns:
+            The HTTP response headers and a summary string.
 
-        if not content_type:
-            raise ResponseError("Missing 'Content-Type' header from `/versions`.")
+        """
 
-        if not all(header in content_type for header in expected_headers):
+        if expected_parameter not in content_type:
             raise ResponseError(
-                f"Incorrect 'Content-Type' header {';'.join(content_type)!r} "
-                f"instead of the minimum expected {';'.join(expected_headers)!r}"
+                f"Incorrect 'Content-Type' header {';'.join(content_type)!r}.\n"
+                f"Missing expected parameter {expected_parameter!r}"
             )
 
-        return response, "`/versions` response had correct headers."
+        return (
+            content_type,
+            "`/versions` response had expected Content-Type parameter {expected_header}.",
+        )
 
     def _test_as_type(self) -> None:
         """Tests that the base URL of the validator (i.e. with no