Require IDs to be UUIDs in URLS

We mostly rely on the API returning a 404 to generate 404s for trying
to get things with non-UUID IDs. This is fine, except our tests often
mock these API calls. So it could look like everything is working fine,
except the thing your passing in might never be a valid UUID, and thus
would 404 in a non-test environment.

So this commit:
1. uses the `uuid` URL converter everywhere there’s something that looks
   like an ID in a URL parameter
2.  adds a test which automates checking for 1.

tests/app/main/views/test_uploads.py

@@ -50,8 +50,14 @@ def test_get_upload_letter(client_request):
     assert normalize_spaces(page.find('label', class_='file-upload-button').text) == 'Choose file'
 
 
-def test_post_upload_letter_redirects_for_valid_file(mocker, active_user_with_permissions, service_one, client_request):
-    mocker.patch('uuid.uuid4', return_value='fake-uuid')
+def test_post_upload_letter_redirects_for_valid_file(
+    mocker,
+    active_user_with_permissions,
+    service_one,
+    client_request,
+    fake_uuid,
+):
+    mocker.patch('uuid.uuid4', return_value=fake_uuid)
     antivirus_mock = mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
     mocker.patch(
         'app.main.views.uploads.sanitise_letter',
@@ -76,7 +82,7 @@ def test_post_upload_letter_redirects_for_valid_file(mocker, active_user_with_pe
 
     mock_s3.assert_called_once_with(
         b'The sanitised content',
-        file_location='service-{}/fake-uuid.pdf'.format(SERVICE_ONE_ID),
+        file_location='service-{}/{}.pdf'.format(SERVICE_ONE_ID, fake_uuid),
         status='valid',
         page_count=1,
         filename='tests/test_pdf_files/one_page_pdf.pdf'
@@ -85,7 +91,7 @@ def test_post_upload_letter_redirects_for_valid_file(mocker, active_user_with_pe
     assert page.find('h1').text == 'tests/test_pdf_files/one_page_pdf.pdf'
     assert not page.find(id='validation-error-message')
 
-    assert page.find('input', {'type': 'hidden', 'name': 'file_id', 'value': 'fake-uuid'})
+    assert page.find('input', {'type': 'hidden', 'name': 'file_id', 'value': fake_uuid})
     assert page.find('button', {'type': 'submit'}).text == 'Send 1 letter'
 
 
@@ -94,6 +100,7 @@ def test_post_upload_letter_shows_letter_preview_for_valid_file(
     active_user_with_permissions,
     service_one,
     client_request,
+    fake_uuid,
 ):
     letter_template = {'template_type': 'letter',
                        'reply_to_text': '',
@@ -101,7 +108,7 @@ def test_post_upload_letter_shows_letter_preview_for_valid_file(
                        'subject': 'hi',
                        'content': 'my letter'}
 
-    mocker.patch('uuid.uuid4', return_value='fake-uuid')
+    mocker.patch('uuid.uuid4', return_value=fake_uuid)
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
     mocker.patch(
         'app.main.views.uploads.sanitise_letter',
@@ -137,7 +144,7 @@ def test_post_upload_letter_shows_letter_preview_for_valid_file(
         assert img['src'] == url_for(
             '.view_letter_upload_as_preview',
             service_id=SERVICE_ONE_ID,
-            file_id='fake-uuid',
+            file_id=fake_uuid,
             page=page_no)
 
 
@@ -211,8 +218,8 @@ def test_post_choose_upload_file_when_file_is_malformed(mocker, client_request):
     assert normalize_spaces(page.find('label', class_='file-upload-button').text) == 'Upload your file again'
 
 
-def test_post_upload_letter_with_invalid_file(mocker, client_request):
-    mocker.patch('uuid.uuid4', return_value='fake-uuid')
+def test_post_upload_letter_with_invalid_file(mocker, client_request, fake_uuid):
+    mocker.patch('uuid.uuid4', return_value=fake_uuid)
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
     mock_s3 = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
 
@@ -241,7 +248,7 @@ def test_post_upload_letter_with_invalid_file(mocker, client_request):
 
         mock_s3.assert_called_once_with(
             file_contents,
-            file_location='service-{}/fake-uuid.pdf'.format(SERVICE_ONE_ID),
+            file_location='service-{}/{}.pdf'.format(SERVICE_ONE_ID, fake_uuid),
             status='invalid',
             page_count=1,
             filename='tests/test_pdf_files/one_page_pdf.pdf',
@@ -253,14 +260,14 @@ def test_post_upload_letter_with_invalid_file(mocker, client_request):
     assert not page.find('button', {'type': 'submit'})
 
 
-def test_post_upload_letter_shows_letter_preview_for_invalid_file(mocker, client_request):
+def test_post_upload_letter_shows_letter_preview_for_invalid_file(mocker, client_request, fake_uuid):
     letter_template = {'template_type': 'letter',
                        'reply_to_text': '',
                        'postage': 'first',
                        'subject': 'hi',
                        'content': 'my letter'}
 
-    mocker.patch('uuid.uuid4', return_value='fake-uuid')
+    mocker.patch('uuid.uuid4', return_value=fake_uuid)
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
     mocker.patch('app.main.views.uploads.upload_letter_to_s3')
     mock_sanitise_response = Mock()
@@ -287,13 +294,17 @@ def test_post_upload_letter_shows_letter_preview_for_invalid_file(mocker, client
     assert letter_images[0]['src'] == url_for(
         '.view_letter_upload_as_preview',
         service_id=SERVICE_ONE_ID,
-        file_id='fake-uuid',
+        file_id=fake_uuid,
         page=1
     )
 
 
-def test_post_upload_letter_does_not_upload_to_s3_if_template_preview_raises_unknown_error(mocker, client_request):
-    mocker.patch('uuid.uuid4', return_value='fake-uuid')
+def test_post_upload_letter_does_not_upload_to_s3_if_template_preview_raises_unknown_error(
+    mocker,
+    client_request,
+    fake_uuid,
+):
+    mocker.patch('uuid.uuid4', return_value=fake_uuid)
     mocker.patch('app.main.views.uploads.antivirus_client.scan', return_value=True)
     mock_s3 = mocker.patch('app.main.views.uploads.upload_letter_to_s3')
 
@@ -311,7 +322,13 @@ def test_post_upload_letter_does_not_upload_to_s3_if_template_preview_raises_unk
     assert not mock_s3.called
 
 
-def test_uploaded_letter_preview(mocker, active_user_with_permissions, service_one, client_request):
+def test_uploaded_letter_preview(
+    mocker,
+    active_user_with_permissions,
+    service_one,
+    client_request,
+    fake_uuid,
+):
     mocker.patch('app.main.views.uploads.service_api_client')
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value={
         'filename': 'my_letter.pdf', 'page_count': '1', 'status': 'valid'})
@@ -322,7 +339,7 @@ def test_uploaded_letter_preview(mocker, active_user_with_permissions, service_o
     page = client_request.get(
         'main.uploaded_letter_preview',
         service_id=SERVICE_ONE_ID,
-        file_id='fake-uuid',
+        file_id=fake_uuid,
         original_filename='my_letter.pdf',
         page_count=1,
         status='valid',
@@ -333,7 +350,11 @@ def test_uploaded_letter_preview(mocker, active_user_with_permissions, service_o
     assert page.find('div', class_='letter-sent')
 
 
-def test_uploaded_letter_preview_does_not_show_send_button_if_service_in_trial_mode(mocker, client_request):
+def test_uploaded_letter_preview_does_not_show_send_button_if_service_in_trial_mode(
+    mocker,
+    client_request,
+    fake_uuid,
+):
     mocker.patch('app.main.views.uploads.service_api_client')
     mocker.patch('app.main.views.uploads.get_letter_metadata', return_value={
         'filename': 'my_letter.pdf', 'page_count': '1', 'status': 'valid'})
@@ -342,7 +363,7 @@ def test_uploaded_letter_preview_does_not_show_send_button_if_service_in_trial_m
     page = client_request.get(
         'main.uploaded_letter_preview',
         service_id=SERVICE_ONE_ID,
-        file_id='fake-uuid',
+        file_id=fake_uuid,
         original_filename='my_letter.pdf',
         page_count=1,
         status='valid',
@@ -359,6 +380,7 @@ def test_uploaded_letter_preview_image_shows_overlay_when_content_outside_printa
     mocker,
     logged_in_client,
     mock_get_service,
+    fake_uuid,
 ):
     mocker.patch(
         'app.main.views.uploads.get_letter_pdf_and_metadata',
@@ -369,7 +391,7 @@ def test_uploaded_letter_preview_image_shows_overlay_when_content_outside_printa
         return_value=make_response('page.html', 200))
 
     logged_in_client.get(
-        url_for('main.view_letter_upload_as_preview', file_id='fake-uuid', service_id=SERVICE_ONE_ID, page=1)
+        url_for('main.view_letter_upload_as_preview', file_id=fake_uuid, service_id=SERVICE_ONE_ID, page=1)
     )
 
     template_preview_mock.assert_called_once_with('pdf_file', '1')
@@ -387,6 +409,7 @@ def test_uploaded_letter_preview_image_does_not_show_overlay_if_no_content_outsi
     logged_in_client,
     mock_get_service,
     metadata,
+    fake_uuid,
 ):
     mocker.patch(
         'app.main.views.uploads.get_letter_pdf_and_metadata',
@@ -397,7 +420,7 @@ def test_uploaded_letter_preview_image_does_not_show_overlay_if_no_content_outsi
         return_value=make_response('page.html', 200))
 
     logged_in_client.get(
-        url_for('main.view_letter_upload_as_preview', file_id='fake-uuid', service_id=SERVICE_ONE_ID, page=1)
+        url_for('main.view_letter_upload_as_preview', file_id=fake_uuid, service_id=SERVICE_ONE_ID, page=1)
     )
 
     template_preview_mock.assert_called_once_with('pdf_file', '1')