improved idmaker name selection in case of duplicate ids

_pytest/python.py

@@ -7,6 +7,7 @@ import re
 import types
 import sys
 import math
+import collections
 
 import py
 import pytest
@@ -1152,9 +1153,14 @@ def _idvalset(idx, valset, argnames, idfn, ids):
 def idmaker(argnames, argvalues, idfn=None, ids=None):
     ids = [_idvalset(valindex, valset, argnames, idfn, ids)
            for valindex, valset in enumerate(argvalues)]
-    if len(set(ids)) < len(ids):
-        # user may have provided a bad idfn which means the ids are not unique
-        ids = [str(i) + testid for i, testid in enumerate(ids)]
+    duplicates = [testid for testid in ids if ids.count(testid) > 1]
+    if duplicates:
+        # The ids are not unique
+        counters = collections.defaultdict(lambda: 0)
+        for index, testid in enumerate(ids):
+            if testid in duplicates:
+                ids[index] = testid + str(counters[testid])
+                counters[testid] += 1
     return ids
 
 def showfixtures(config):

testing/python/metafunc.py

@@ -238,9 +238,9 @@ class TestMetafunc:
                                       (20, KeyError()),
                                       ("three", [1, 2, 3]),
         ], idfn=ids)
-        assert result == ["0a-a",
-                          "1a-a",
-                          "2a-a",
+        assert result == ["a-a0",
+                          "a-a1",
+                          "a-a2",
                          ]
 
     @pytest.mark.issue351
@@ -267,10 +267,9 @@ class TestMetafunc:
 
     def test_idmaker_with_ids_unique_names(self):
         from _pytest.python import idmaker
-        result = idmaker(("a", "b"), [(1, 2),
-                                      (3, 4)],
-                         ids=["a", "a"])
-        assert result == ["0a", "1a"]
+        result = idmaker(("a"), [1,2,3,4,5],
+                         ids=["a", "a", "b", "c", "b"])
+        assert result == ["a0", "a1", "b0", "c", "b1"]
 
     def test_addcall_and_parametrize(self):
         def func(x, y): pass
@@ -834,8 +833,8 @@ class TestMetafuncFunctional:
         result = testdir.runpytest("-v")
         assert result.ret == 1
         result.stdout.fnmatch_lines_random([
-            "*test_function*0a*PASSED",
-            "*test_function*1a*FAILED"
+            "*test_function*a0*PASSED",
+            "*test_function*a1*FAILED"
         ])
 
     @pytest.mark.parametrize(("scope", "length"),