diff --git a/tests/app/template/test_rest.py b/tests/app/template/test_rest.py
index 99889e238..6dac7e084 100644
--- a/tests/app/template/test_rest.py
+++ b/tests/app/template/test_rest.py
@@ -3,6 +3,7 @@ import json
 import random
 import string
 from datetime import datetime, timedelta
+from json import JSONDecodeError
 
 import botocore
 import pytest
@@ -828,7 +829,7 @@ def test_preview_letter_template_by_id_valid_file_type(
         with requests_mock.Mocker() as request_mock:
             content = b'\x00\x01'
 
-            request_mock.post(
+            mock_post = request_mock.post(
                 'http://localhost/notifications-template-preview/preview.pdf',
                 content=content,
                 headers={'X-pdf-page-count': '1'},
@@ -842,6 +843,7 @@ def test_preview_letter_template_by_id_valid_file_type(
                 file_type='pdf'
             )
 
+            assert mock_post.last_request.json()
             assert base64.b64decode(resp['content']) == content
 
 
@@ -859,7 +861,7 @@ def test_preview_letter_template_by_id_template_preview_500(
         with requests_mock.Mocker() as request_mock:
             content = b'\x00\x01'
 
-            request_mock.post(
+            mock_post = request_mock.post(
                 'http://localhost/notifications-template-preview/preview.pdf',
                 content=content,
                 headers={'X-pdf-page-count': '1'},
@@ -874,11 +876,11 @@ def test_preview_letter_template_by_id_template_preview_500(
                 _expected_status=500
             )
 
+            assert mock_post.last_request.json()
             assert 'Status code: 404' in resp['message']
             assert 'Error generating preview letter for {}'.format(sample_letter_notification.id) in resp['message']
 
 
-
 def test_preview_letter_template_precompiled_pdf_file_type(
         notify_api,
         client,
@@ -980,7 +982,7 @@ def test_preview_letter_template_precompiled_png_file_type(
 
             mock_get_letter_pdf = mocker.patch('app.template.rest.get_letter_pdf', return_value=pdf_content)
 
-            request_mock.post(
+            mock_post = request_mock.post(
                 'http://localhost/notifications-template-preview/precompiled-preview.png',
                 content=png_content,
                 headers={'X-pdf-page-count': '1'},
@@ -994,6 +996,8 @@ def test_preview_letter_template_precompiled_png_file_type(
                 file_type='png'
             )
 
+            with pytest.raises(JSONDecodeError):
+                mock_post.last_request.json()
             assert mock_get_letter_pdf.called_once_with(notification)
             assert base64.b64decode(resp['content']) == png_content
 
@@ -1025,7 +1029,7 @@ def test_preview_letter_template_precompiled_png_template_preview_500_error(
 
             mocker.patch('app.template.rest.get_letter_pdf', return_value=pdf_content)
 
-            request_mock.post(
+            mock_post = request_mock.post(
                 'http://localhost/notifications-template-preview/precompiled-preview.png',
                 content=png_content,
                 headers={'X-pdf-page-count': '1'},
@@ -1041,6 +1045,9 @@ def test_preview_letter_template_precompiled_png_template_preview_500_error(
 
             )
 
+            with pytest.raises(JSONDecodeError):
+                mock_post.last_request.json()
+
 
 def test_preview_letter_template_precompiled_png_template_preview_400_error(
         notify_api,
@@ -1069,7 +1076,7 @@ def test_preview_letter_template_precompiled_png_template_preview_400_error(
 
             mocker.patch('app.template.rest.get_letter_pdf', return_value=pdf_content)
 
-            request_mock.post(
+            mock_post = request_mock.post(
                 'http://localhost/notifications-template-preview/precompiled-preview.png',
                 content=png_content,
                 headers={'X-pdf-page-count': '1'},
@@ -1082,5 +1089,7 @@ def test_preview_letter_template_precompiled_png_template_preview_400_error(
                 notification_id=notification.id,
                 file_type='png',
                 _expected_status=500
-
             )
+
+            with pytest.raises(JSONDecodeError):
+                mock_post.last_request.json()