Fix error message when recipient column missing

When your CSV file is missing the recipient column (eg ‘phone number’
or ‘email address’) we give you a helpful error message telling you that
this is the case.

When we changed the recipient column to be columns, plural, we didn’t
update the code that generated the error message. So you would get
errors that looked this like this:

> Your file needs to have a column called ‘’

This commit fixes the error message.

tests/app/main/views/test_send.py

@@ -115,6 +115,39 @@ def test_upload_csvfile_with_errors_shows_check_page_with_errors(
         assert 'Re-upload your file' in content
 
 
+def test_upload_csvfile_with_no_recipient_column_shows_error(
+    logged_in_client,
+    mocker,
+    mock_get_service_template_with_placeholders,
+    mock_s3_upload,
+    mock_get_users_by_service,
+    mock_get_detailed_service_for_today,
+    fake_uuid,
+):
+
+    mocker.patch(
+        'app.main.views.send.s3download',
+        return_value="""
+            telephone,name
+            +447700900986
+        """
+    )
+
+    response = logged_in_client.post(
+        url_for('main.send_messages', service_id=fake_uuid, template_id=fake_uuid),
+        data={'file': (BytesIO(''.encode('utf-8')), 'invalid.csv')},
+        follow_redirects=True,
+    )
+
+    assert response.status_code == 200
+    page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
+    assert ' '.join(page.select('.banner-dangerous')[0].text.split()) == (
+        'Your file needs to have a column called ‘phone number’ '
+        'Your file has columns called ‘telephone’ and ‘name’. '
+        'Skip to file contents'
+    )
+
+
 def test_upload_csv_invalid_extension(
     logged_in_client,
     api_user_active,