Remove uses of .assert_not_called

I prefer to avoid `assert_not_called`, because if I make a typo like
this, the tests will still pass:
```
    app.invite_api_client.create_invite.asset_not_called()
```

It’s harder to have a false positive with the statement written this
way:
```
    assert app.invite_api_client.create_invite.called is False
```

tests/app/main/views/test_api_integration.py

@@ -301,7 +301,7 @@ def test_cant_create_normal_api_key_in_trial_mode(
         },
         _expected_status=400,
     )
-    mock_post.assert_not_called()
+    assert mock_post.called is False
 
 
 def test_should_show_confirm_revoke_api_key(

tests/app/main/views/test_jobs.py

@@ -642,7 +642,7 @@ def test_dont_cancel_letter_job_when_to_early_to_cancel(
         job_id=str(job_id),
         _expected_status=200,
     )
-    mock_cancel.assert_not_called()
+    assert mock_cancel.called is False
     flash_message = normalize_spaces(page.find('div', class_='banner-dangerous').text)
 
     assert 'We are still processing these letters, please try again in a minute.' in flash_message

tests/app/main/views/test_letter_branding.py

@@ -92,7 +92,7 @@ def test_update_letter_branding_with_new_valid_file(
     assert page.select_one('#name').attrs.get('value') == 'HM Government'
 
     assert mock_s3_upload.called
-    mock_delete_temp_files.assert_not_called()
+    assert mock_delete_temp_files.called is False
 
 
 def test_update_letter_branding_when_uploading_invalid_file(
@@ -163,7 +163,7 @@ def test_update_letter_branding_with_original_file_and_new_details(
     assert response.status_code == 200
     assert page.find('h1').text == 'Letter branding'
 
-    mock_upload_logos.assert_not_called()
+    assert mock_upload_logos.called is False
 
     mock_client_update.assert_called_once_with(
         branding_id=fake_uuid,
@@ -343,7 +343,7 @@ def test_create_letter_branding_when_uploading_valid_file(
 
     assert page.select_one('#logo-img > img').attrs['src'].endswith(expected_temp_filename)
     assert mock_s3_upload.called
-    mock_delete_temp_files.assert_not_called()
+    assert mock_delete_temp_files.called is False
 
 
 def test_create_letter_branding_fails_validation_when_uploading_SVG_with_embedded_image(
@@ -372,7 +372,7 @@ def test_create_letter_branding_fails_validation_when_uploading_SVG_with_embedde
 
     assert page.findAll('div', {'id': 'logo-img'}) == []
 
-    mock_s3_upload.assert_not_called()
+    assert mock_s3_upload.called is False
 
 
 def test_create_letter_branding_when_uploading_invalid_file(platform_admin_client):

tests/app/main/views/test_platform_admin.py

@@ -854,7 +854,7 @@ def test_get_notifications_sent_by_service_validates_form(mocker, client_request
     for error in errors:
         assert 'Not a valid date value' in error.text
 
-    mock_get_stats_from_api.assert_not_called()
+    assert mock_get_stats_from_api.called is False
 
 
 def test_usage_for_all_services_when_no_results_for_date(client_request, platform_admin_user, mocker):

tests/app/main/views/test_returned_letters.py

@@ -183,4 +183,4 @@ def test_returned_letters_reports_returns_404_for_bad_date(
                                 service_id=SERVICE_ONE_ID,
                                 reported_at='19-12-2019',
                                 _expected_status=404)
-    mock.assert_not_called()
+    assert mock.called is False

tests/app/main/views/test_service_settings.py

@@ -789,8 +789,8 @@ def test_service_name_change_confirm_handles_expired_session(
         service_id=SERVICE_ONE_ID,
         _follow_redirects=True
     )
-    mock_verify_password.assert_not_called()
-    mock_update_service.assert_not_called()
+    assert mock_verify_password.called is False
+    assert mock_update_service.called is False
 
     assert page.find('div', 'banner-dangerous').text.strip() == "The change you made was not saved. Please try again."
 
@@ -2378,14 +2378,14 @@ def test_service_verify_reply_to_address(
             mock_update_reply_to_email_address.assert_called_once_with(
                 SERVICE_ONE_ID, "123", email_address=notification["to"], is_default=is_default
             )
-            mock_add_reply_to_email_address.assert_not_called()
+            assert mock_add_reply_to_email_address.called is False
         else:
             mock_add_reply_to_email_address.assert_called_once_with(
                 SERVICE_ONE_ID, email_address=notification["to"], is_default=is_default
             )
-            mock_update_reply_to_email_address.assert_not_called()
+            assert mock_update_reply_to_email_address.called is False
     else:
-        mock_add_reply_to_email_address.assert_not_called()
+        assert mock_add_reply_to_email_address.called is False
     if status == "permanent-failure":
         assert page.find('input', type='email').attrs["value"] == notification["to"]
 
@@ -2414,7 +2414,7 @@ def test_add_reply_to_email_address_fails_if_notification_not_delivered_in_45_se
     )
     expected_banner = page.find_all('div', class_='banner-dangerous')[0]
     assert 'There’s a problem with your reply-to address' in expected_banner.text.strip()
-    mock_add_reply_to_email_address.assert_not_called()
+    assert mock_add_reply_to_email_address.called is False
 
 
 @pytest.mark.parametrize('letter_contact_blocks, data, api_default_args', [
@@ -2620,7 +2620,7 @@ def test_edit_reply_to_email_address_goes_straight_to_update_if_address_not_chan
         email_address="test@example.com",
         is_default=api_default_args
     )
-    mock_verify.assert_not_called()
+    assert mock_verify.called is False
 
 
 @pytest.mark.parametrize('url', [
@@ -2662,7 +2662,7 @@ def test_add_edit_reply_to_email_address_goes_straight_to_update_if_address_not_
     assert page.find('h1').text == "Reply-to email addresses"
     assert error_message in page.find('div', class_='banner-dangerous').text
 
-    mock_update_reply_to_email_address.assert_not_called()
+    assert mock_update_reply_to_email_address.called is False
 
 
 @pytest.mark.parametrize('reply_to_address, expected_link_text, partial_href', [
@@ -4482,8 +4482,8 @@ def test_show_branding_request_page_when_no_branding_is_set(
         '.branding_request', service_id=SERVICE_ONE_ID, branding_type=branding_type
     )
 
-    mock_get_email_branding.assert_not_called()
-    mock_get_letter_branding_by_id.assert_not_called()
+    assert mock_get_email_branding.called is False
+    assert mock_get_letter_branding_by_id.called is False
 
     if expected_options:
         assert [
@@ -4555,8 +4555,8 @@ def test_show_branding_request_page_when_no_branding_is_set_but_organisation_exi
         '.branding_request', service_id=SERVICE_ONE_ID, branding_type=branding_type
     )
 
-    mock_get_email_branding.assert_not_called()
-    mock_get_letter_branding_by_id.assert_not_called()
+    assert mock_get_email_branding.called is False
+    assert mock_get_letter_branding_by_id.called is False
 
     assert [
         (
@@ -4599,8 +4599,8 @@ def test_show_branding_request_page_when_no_branding_is_set_but_organisation_exi
         '.branding_request', service_id=SERVICE_ONE_ID, branding_type=branding_type
     )
 
-    mock_get_email_branding.assert_not_called()
-    mock_get_letter_branding_by_id.assert_not_called()
+    assert mock_get_email_branding.called is False
+    assert mock_get_letter_branding_by_id.called is False
 
     assert [
         (

tests/app/main/views/test_two_factor.py

@@ -331,7 +331,7 @@ def test_two_factor_email_link_has_expired(
     page = BeautifulSoup(response.data.decode('utf-8'), 'html.parser')
 
     assert page.h1.text.strip() == 'The link has expired'
-    mock_send_verify_code.assert_not_called
+    assert mock_send_verify_code.called is False
 
 
 def test_two_factor_email_link_is_invalid(
@@ -367,7 +367,7 @@ def test_two_factor_email_link_is_already_used(
     assert response.status_code == 200
 
     assert page.h1.text.strip() == 'The link has expired'
-    mock_send_verify_code.assert_not_called
+    assert mock_send_verify_code.called is False
 
 
 def test_two_factor_email_link_when_user_is_locked_out(
@@ -387,7 +387,7 @@ def test_two_factor_email_link_when_user_is_locked_out(
     assert response.status_code == 200
 
     assert page.h1.text.strip() == 'The link has expired'
-    mock_send_verify_code.assert_not_called
+    assert mock_send_verify_code.called is False
 
 
 def test_two_factor_email_link_used_when_user_already_logged_in(

tests/app/s3_client/test_s3_logo_client.py

@@ -95,8 +95,8 @@ def test_persist_logo_returns_if_not_temp(client, mocker, fake_uuid):
     mocked_get_s3_object = mocker.patch('app.s3_client.s3_logo_client.get_s3_object')
     mocked_delete_s3_object = mocker.patch('app.s3_client.s3_logo_client.delete_s3_object')
 
-    mocked_get_s3_object.assert_not_called()
-    mocked_delete_s3_object.assert_not_called()
+    assert mocked_get_s3_object.called is False
+    assert mocked_delete_s3_object.called is False
 
 
 def test_permanent_email_logo_name_removes_TEMP_TAG_from_filename(upload_filename, fake_uuid):
@@ -163,7 +163,7 @@ def test_does_not_delete_non_temp_email_file(client, mocker):
     with pytest.raises(ValueError) as error:
         delete_email_temp_file(filename)
 
-    mocked_delete_s3_object.assert_not_called
+    assert mocked_delete_s3_object.called is False
     assert str(error.value) == 'Not a temp file: {}'.format(filename)
 
 
@@ -183,5 +183,5 @@ def test_does_not_delete_non_temp_letter_file(mocker, fake_uuid):
     with pytest.raises(ValueError) as error:
         delete_letter_temp_file(svg_filename)
 
-    mocked_delete_s3_object.assert_not_called
+    assert mocked_delete_s3_object.called is False
     assert str(error.value) == 'Not a temp file: {}'.format(svg_filename)