adding negative, none -1 general single-shot test case

test/unit/test_base64_stream.py

@@ -136,8 +136,9 @@ def build_test_cases():
     for size in (0, 1, 2, 3, 4, 5, 6, 7, 222, 1024):
         test_cases.append((size, size, 1, size))
 
-    test_cases.append((1024, None, 1, 1024))  # single-shot
-    test_cases.append((1024, -1, 1, 1024))  # single-shot
+    # general single-shot: not affected by size
+    for single_shot in (None, -1, -99):
+        test_cases.append((1024, single_shot, 1, 1024))
 
     # Odd multiples with operation smaller, equal to, and larger than total
     for rounds in (1, 3, 5):