Enforce use of --no-visited-link-state

We don’t use colour to indicate visited link state.

To acheive this we use the `govuk-link--no-visited-link-state` modifier
from GOV.UK Frontend.

In case someone misses this, this commit adds a test which checks for
any links missing this class.

Author: quis

app/templates/views/document-download/confirm-email-address.html

@@ -20,9 +20,9 @@
     <p class="govuk-body">
       If you have any questions,
       {% if current_service.contact_details_type == "url" %}
-        <a href="{{ current_service.contact_link }}" class="govuk-link" rel="noreferrer"> contact {{ current_service.name }}</a>.
+        <a href="{{ current_service.contact_link }}" class="govuk-link govuk-link--no-visited-state" rel="noreferrer"> contact {{ current_service.name }}</a>.
       {% elif current_service.contact_details_type == "email_address" %}
-        email <a href="mailto:{{ current_service.contact_link }}" class="govuk-link">{{ current_service.contact_link }}</a>.
+        email <a href="mailto:{{ current_service.contact_link }}" class="govuk-link govuk-link--no-visited-state">{{ current_service.contact_link }}</a>.
       {% else %}
         call {{ current_service.contact_link }}.
       {% endif %}

app/templates/views/document-download/index.html

@@ -17,9 +17,9 @@
     <p class="govuk-body">
       If you have any questions,
       {% if current_service.contact_details_type == "url" %}
-        <a href="{{ current_service.contact_link }}" class="govuk-link" rel="noreferrer"> contact {{ current_service.name }}</a>.
+        <a href="{{ current_service.contact_link }}" class="govuk-link govuk-link--no-visited-state" rel="noreferrer"> contact {{ current_service.name }}</a>.
       {% elif current_service.contact_details_type == "email_address" %}
-        email <a href="mailto:{{ current_service.contact_link }}" class="govuk-link">{{ current_service.contact_link }}</a>.
+        email <a href="mailto:{{ current_service.contact_link }}" class="govuk-link govuk-link--no-visited-state">{{ current_service.contact_link }}</a>.
       {% else %}
         call {{ current_service.contact_link }}.
       {% endif %}

app/templates/views/returned-letters.html

@@ -23,7 +23,7 @@
 {% endif %}
 
 <p class="bottom-gutter">
-  <a download href="{{ url_for('main.returned_letters_report', service_id=current_service.id, reported_at=reported_at) }}" class="govuk-link heading-small">Download this report (<abbr title="Comma separated values">CSV</abbr>)</a>
+  <a download href="{{ url_for('main.returned_letters_report', service_id=current_service.id, reported_at=reported_at) }}" class="govuk-link govuk-link--no-visited-state heading-small">Download this report (<abbr title="Comma separated values">CSV</abbr>)</a>
 </p>
 
 <div class="dashboard-table">

app/templates/views/templates/email-template-files/email_file.html

@@ -31,6 +31,7 @@
                 template_id=template_id,
                 template_email_file_id=template_email_file_data.id),
                 "text": "Change",
+                "classes": "govuk-link--no-visited-state",
               }
             ]
           }
@@ -49,6 +50,7 @@
                 "href": url_for("main.change_data_retention_period", service_id=current_service.id,
                 template_id=template_id,template_email_file_id=template_email_file_data.id),
                 "text": "Change",
+                "classes": "govuk-link--no-visited-state",
               }
             ]
           }
@@ -67,7 +69,7 @@
                 "href": url_for("main.change_email_validation", service_id=current_service.id,
                 template_id=template_id,template_email_file_id=template_email_file_data.id),
                 "text": "Change",
-                "classes": "govuk-link--no-visited-state"
+                "classes": "govuk-link--no-visited-state",
               }
             ]
           },

tests/conftest.py

@@ -3062,6 +3062,8 @@ def get_url(
             if _test_for_non_smart_quotes:
                 ClientRequest.test_for_non_smart_quotes(page)
 
+            ClientRequest.test_for_visited_links(page)
+
             ClientRequest.test_for_missing_en_dashes(page)
 
             if _test_for_script_csp_nonce:
@@ -3196,6 +3198,23 @@ def test_for_elements_without_class(page):
                     "Use govuk-heading-l or set error_summary_enabled=False"
                 )
 
+        @staticmethod
+        def test_for_visited_links(page):
+            for element in page.select(f"a.govuk-link"):
+                if set(element["class"]).intersection({
+                    # Link modifiers which already override the visited state
+                    "govuk-link--destructive",
+                    "govuk-link--inverse",
+                    "govuk-link--text-colour",
+                }):
+                    continue
+                assert 'govuk-link--no-visited-state' in element["class"], (
+                    f"Found an <a> element with a visited link state:\n"
+                    f"    {element}\n"
+                    f"\n"
+                    f'(you probably want to add govuk-link--no-visited-state to the class attribute")'
+                )
+
         @staticmethod
         def test_forms_have_an_action_set(page):
             assert not len(