fix: don't show matched fields if there is nothing to show

Datahub was returning a spurious 'tags: []' value, which
doesn't require rendering anything. This meant we were showing
an empty matched fields even when no search query was entered.

templates/partial/search_result.html

@@ -59,12 +59,14 @@ <h3 class="govuk-heading-m govuk-!-margin-bottom-2">
             </li>
           {% endswitch %}
 
-          {% if result.matches %}
-            <li>
-              <span class="govuk-!-font-weight-bold">{% translate "Matched fields:" %}</span>
-              <span>{{ result.matches|lookup:readable_match_reasons|join:", " }}</span>
-            </li>
-          {% endif %}
+          {% with match_reasons=result.matches|lookup:readable_match_reasons|join:", " %}
+            {% if match_reasons %}
+              <li>
+                <span class="govuk-!-font-weight-bold">{% translate "Matched fields:" %}</span>
+                <span>{{ match_reasons }}</span>
+              </li>
+            {% endif %}
+          {% endwith %}
         </ul>
         <hr class="govuk-section-break govuk-section-break--m govuk-section-break--visible">
       </div>

tests/integration/test_search_result_metadata.py

@@ -0,0 +1,48 @@
+import pytest
+from data_platform_catalogue.search_types import ResultType, SearchResult
+
+from tests.conftest import mock_search_response
+
+
+@pytest.mark.slow
+class TestSearchResultMetadata:
+    """
+    Given I am on a search page
+    When I look at the metadata underneath a search result
+    Then "matched fields" should only be shown if I entered a search term
+    """
+
+    @pytest.fixture(autouse=True)
+    def setup(self, live_server, selenium):
+        self.selenium = selenium
+        self.live_server_url = live_server.url
+
+    def test_matched_fields_hidden(self, mock_catalogue):
+        result = SearchResult(
+            urn="fake-urn",
+            result_type=ResultType.DATABASE,
+            name="abc",
+            fully_qualified_name="abc",
+            description="bla bla bla",
+            matches={"tags": []},
+        )
+        mock_search_response(mock_catalogue, total_results=1, page_results=[result])
+
+        self.selenium.get(f"{self.live_server_url}/search")
+
+        assert "Matched fields:" not in self.selenium.page_source
+
+    def test_matched_fields_shown(self, mock_catalogue):
+        result = SearchResult(
+            urn="fake-urn",
+            result_type=ResultType.DATABASE,
+            name="abc",
+            fully_qualified_name="abc",
+            description="bla bla bla",
+            matches={"tags": [], "description": "abc"},
+        )
+        mock_search_response(mock_catalogue, total_results=1, page_results=[result])
+
+        self.selenium.get(f"{self.live_server_url}/search?query=bla")
+
+        assert "Matched fields:" in self.selenium.page_source