Duplicated parameters in parametrize marker (#11489)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>

AUTHORS

@@ -367,6 +367,7 @@ Tadek Teleżyński
 Takafumi Arakaki
 Taneli Hukkinen
 Tanvi Mehta
+Tanya Agarwal
 Tarcisio Fischer
 Tareq Alayan
 Tatiana Ovary

changelog/11456.bugfix.rst

@@ -0,0 +1,4 @@
+Parametrized tests now *really do* ensure that the ids given to each input are unique - for
+example, ``a, a, a0`` now results in ``a1, a2, a0`` instead of the previous (buggy) ``a0, a1, a0``.
+This necessarily means changing nodeids where these were previously colliding, and for
+readability adds an underscore when non-unique ids end in a number.

src/_pytest/python.py

@@ -1002,8 +1002,18 @@ class IdMaker:
             # Suffix non-unique IDs to make them unique.
             for index, id in enumerate(resolved_ids):
                 if id_counts[id] > 1:
-                    resolved_ids[index] = f"{id}{id_suffixes[id]}"
+                    suffix = ""
+                    if id[-1].isdigit():
+                        suffix = "_"
+                    new_id = f"{id}{suffix}{id_suffixes[id]}"
+                    while new_id in set(resolved_ids):
                         id_suffixes[id] += 1
+                        new_id = f"{id}{suffix}{id_suffixes[id]}"
+                    resolved_ids[index] = new_id
+                    id_suffixes[id] += 1
+        assert len(resolved_ids) == len(
+            set(resolved_ids)
+        ), f"Internal error: {resolved_ids=}"
         return resolved_ids
 
     def _resolve_ids(self) -> Iterable[str]:

testing/acceptance_test.py

@@ -341,6 +341,45 @@ class TestGeneralUsage:
         assert res.ret == 0
         res.stdout.fnmatch_lines(["*1 passed*"])
 
+    def test_direct_addressing_selects_duplicates(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.parametrize("a", [1, 2, 10, 11, 2, 1, 12, 11])
+            def test_func(a):
+                pass
+            """
+        )
+        result = pytester.runpytest(p)
+        result.assert_outcomes(failed=0, passed=8)
+
+    def test_direct_addressing_selects_duplicates_1(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.parametrize("a", [1, 2, 10, 11, 2, 1, 12, 1_1,2_1])
+            def test_func(a):
+                pass
+            """
+        )
+        result = pytester.runpytest(p)
+        result.assert_outcomes(failed=0, passed=9)
+
+    def test_direct_addressing_selects_duplicates_2(self, pytester: Pytester) -> None:
+        p = pytester.makepyfile(
+            """
+            import pytest
+
+            @pytest.mark.parametrize("a", ["a","b","c","a","a1"])
+            def test_func(a):
+                pass
+            """
+        )
+        result = pytester.runpytest(p)
+        result.assert_outcomes(failed=0, passed=5)
+
     def test_direct_addressing_notfound(self, pytester: Pytester) -> None:
         p = pytester.makepyfile(
             """