adjust test_parametrized_ids_invalid_type, create list to convert tuples

Ref: pytest-dev#1857 (comment)

src/_pytest/python.py

@@ -1030,7 +1030,7 @@ def _resolve_arg_ids(self, argnames, ids, parameters, item):
 
     def _validate_ids(self, ids, parameters, func_name):
         try:
-            len_ids = len(ids)
+            len(ids)
         except TypeError:
             try:
                 it = iter(ids)
@@ -1039,13 +1039,13 @@ def _validate_ids(self, ids, parameters, func_name):
             else:
                 import itertools
 
-                ids = list(itertools.islice(it, len(parameters)))
-                len_ids = len(ids)
+                new_ids = list(itertools.islice(it, len(parameters)))
+        else:
+            new_ids = list(ids)
 
-        if len_ids != len(parameters):
+        if len(new_ids) != len(parameters):
             msg = "In {}: {} parameter sets specified, with different number of ids: {}"
             fail(msg.format(func_name, len(parameters), len(ids)), pytrace=False)
-        new_ids = ids[:]
         for idx, id_value in enumerate(new_ids):
             if id_value is not None:
                 if isinstance(id_value, int):

testing/python/metafunc.py

@@ -1186,20 +1186,21 @@ def test_temp(temp):
         result.stdout.fnmatch_lines(["* 1 skipped *"])
 
     def test_parametrized_ids_invalid_type(self, testdir):
-        """Tests parametrized with ids as non-strings (#1857)."""
+        """Test error with non-strings/non-ints, without generator (#1857)."""
         testdir.makepyfile(
             """
             import pytest
 
-            @pytest.mark.parametrize("x, expected", [(10, 20), (40, 80)], ids=(None, 2))
+            @pytest.mark.parametrize("x, expected", [(1, 2), (3, 4), (5, 6)], ids=(None, 2, type))
             def test_ids_numbers(x,expected):
                 assert x * 2 == expected
         """
         )
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(
             [
-                "*In test_ids_numbers: ids must be list of strings, found: 2 (type: *'int'>)*"
+                "In test_ids_numbers: ids must be list of strings, "
+                "found: <class 'type'> (type: <class 'type'>) at index 2"
             ]
         )