diff --git a/python/pdo/test/storage.py b/python/pdo/test/storage.py
index 0e4ee1ce..87ce836a 100644
--- a/python/pdo/test/storage.py
+++ b/python/pdo/test/storage.py
@@ -77,19 +77,17 @@ def verify_store_signature(store_response, duration, verifying_key) :
     result = client.store_blocks([block_data], duration=default_duration)
 
     r = verify_store_signature(result, default_duration, client.verifying_key)
-    if 1 != r:
-        raise ValueError("verify_store_signature error: {}".format(r))
-
-    if 'block_ids' not in result:
-        raise ValueError("block_ids not in result")
-
-    block_ids = result['block_ids']
+    if r < 0 :
+        raise RuntimeError("unknown error occured during signature verification; {}".format(r))
+    if r == 0 :
+        raise ValueError("storage signature verification failed")
+       
+    block_ids = result.get('block_ids')
+    if block_ids is None or type(block_ids) != list :
+        raise RuntimeError('invalid response from block store')
+        
     if len(block_ids) != 1:
-        raise ValueError("len of block_ids is not 1: {}".format(len(block_ids)))
-    if list != type(result['block_ids']):
-        raise ValueError("block_ids not a list")
-    if len(result['block_ids']) < 1:
-        raise ValueError("no block in block_ids")
+        raise ValueError("too many blocks stored, expected 1 got {}".format(len(block_ids)))
 
     block_id = result['block_ids'][0]
 
@@ -117,19 +115,20 @@ def verify_store_signature(store_response, duration, verifying_key) :
     block_data.append(os.urandom(10))
     block_data.append(os.urandom(10))
     result = client.store_blocks(block_data, duration=default_duration)
-
-    r = verify_store_signature(result, default_duration, client.verifying_key)
-    if 1 != r:
-        raise ValueError("verify_store_signature error: {}".format(r))
-
-    if 'block_ids' not in result:
-        raise ValueError("block_ids not in result")
-
-    block_ids = result['block_ids']
     logger.info('RESULT: %s', result)
 
+    r = verify_store_signature(result, default_duration, client.verifying_key)
+    if r < 0 :
+        raise RuntimeError("unknown error occured during signature verification; {}".format(r))
+    if r == 0 :
+        raise ValueError("storage signature verification failed")
+
+    block_ids = result.get('block_ids')
+    if block_ids is None or type(block_ids) != list :
+        raise RuntimeError('invalid response from block store')
+        
     if len(block_ids) != 3:
-        raise ValueError("block_ids should contain 3 blocks: {}".format(len(block_ids)))
+        raise ValueError("too many blocks stored, expected 3 got {}".format(len(block_ids)))
 
 except Exception as e :
     logger.error('bulk upload test failed; %s', str(e))