Minor check and unit test for bitpattern_to_val

Author: mdko

pyrtl/helperfuncs.py

@@ -307,6 +307,9 @@ def bitpattern_to_val(bitpattern, *ordered_fields, **named_fields):
         # evaluates to   0b00000000001100100010000010100011
     """
 
+    if not bitpattern:
+        raise PyrtlError('bitpattern must be nonempty')
+
     if len(ordered_fields) > 0 and len(named_fields) > 0:
         raise PyrtlError('named and ordered fields cannot be mixed')
 

tests/test_helperfuncs.py

@@ -454,10 +454,9 @@ def test_error_value_doesnt_fit_in_field(self):
         with self.assertRaises(pyrtl.PyrtlError):
             pyrtl.bitpattern_to_val('iiiiiiirrrrrsssss010iiiii0100011', 1, 65, 4)
 
-    @unittest.skip("This error might not be possible")
-    def test_error_bitlist_and_value_different_sizes(self):
+    def test_error_empty_bitpattern(self):
         with self.assertRaises(pyrtl.PyrtlError):
-            pass
+            pyrtl.bitpattern_to_val('')
 
 
 class TestChop(unittest.TestCase):