Always show 4 items in the example list

If a library has lots of items then the first 3 should be shown, with
a count of how many more there are, for a total of 4 list items:
> a, b, c, and 23 more

If the library only has 4 items then all 4 should be shown, with
consistent use of conjunction and Oxford comma[1]:
> a, b, c, and d

This keeps the lengths of the examples nice and consistent.

1. We use an Oxford comma because it helps disambiguate when an area
itself has a comma or ‘and’ in it, for example ‘Armagh City, Banbridge
and Craigavon’

app/broadcast_areas/repo.py

@@ -121,7 +121,7 @@ class BroadcastAreasRepository(object):
         ),
         area_count AS (SELECT COUNT(*) AS c FROM areas),
         subset_area_count AS (SELECT c - 4 FROM area_count),
-        description_area_names  AS (SELECT name FROM areas ORDER BY name ASC LIMIT 4),
+        description_area_names  AS (SELECT name FROM areas ORDER BY name ASC LIMIT 3),
         description_areas_joined AS (
             SELECT GROUP_CONCAT(name, ", ") FROM description_area_names
         )
@@ -129,6 +129,8 @@ class BroadcastAreasRepository(object):
         CASE (SELECT * FROM subset_area_count)
         WHEN 0 THEN
             (SELECT * FROM description_areas_joined)
+            || ", and "
+            || (SELECT name from areas ORDER BY name DESC limit 1)
         ELSE
             (SELECT * FROM description_areas_joined)
             || ", and "

tests/app/broadcast_areas/test_broadcast_area.py

@@ -48,20 +48,20 @@ def test_loads_areas_from_library():
 
 def test_examples():
     countries = broadcast_area_libraries.get('countries').get_examples()
-    assert countries == 'England, Northern Ireland, Scotland, Wales'
+    assert countries == 'England, Northern Ireland, Scotland, and Wales'
 
     regions = broadcast_area_libraries.get('regions-of-england').get_examples()
-    assert regions == 'East Midlands, East of England, London, North East, and 5 more…'
+    assert regions == 'East Midlands, East of England, London, and 5 more…'
 
     counties = broadcast_area_libraries.get(
         'counties-and-unitary-authorities-in-england-and-wales',
     ).get_examples()
-    assert counties == 'Barking and Dagenham, Barnet, Barnsley, Bath and North East Somerset, and 170 more…'
+    assert counties == 'Barking and Dagenham, Barnet, Barnsley, and 170 more…'
 
     wards = broadcast_area_libraries.get(
         'electoral-wards-of-the-united-kingdom',
     ).get_examples()
-    assert wards == 'Aberdeen City, Aberdeenshire, Adur, Allerdale, and 375 more…'
+    assert wards == 'Aberdeen City, Aberdeenshire, Adur, and 375 more…'
 
 
 @pytest.mark.parametrize('id', (

tests/app/main/views/test_broadcast.py

@@ -299,7 +299,7 @@ def test_choose_broadcast_library_page(
     ])
 
     assert normalize_spaces(page.select('.file-list-hint-large')[1].text) == (
-        'England, Northern Ireland, Scotland, Wales'
+        'England, Northern Ireland, Scotland, and Wales'
     )
 
     assert page.select_one('a.file-list-filename-large.govuk-link')['href'] == url_for(