Auto generate excessive long parametrized ids

src/_pytest/python.py

@@ -1181,19 +1181,25 @@ def _idval(
         if hook_id:
             return hook_id
 
+    modified_val = None  # empty strings are valid as val
     if isinstance(val, STRING_TYPES):
-        return _ascii_escaped_by_config(val, config)
+        modified_val = _ascii_escaped_by_config(val, config)
     elif val is None or isinstance(val, (float, int, bool)):
-        return str(val)
+        modified_val = str(val)
     elif isinstance(val, REGEX_TYPE):
-        return ascii_escaped(val.pattern)
+        modified_val = ascii_escaped(val.pattern)
     elif isinstance(val, enum.Enum):
-        return str(val)
+        modified_val = str(val)
     elif isinstance(getattr(val, "__name__", None), str):
         # name of a class, function, module, etc.
-        name = getattr(val, "__name__")  # type: str
-        return name
-    return str(argname) + str(idx)
+        modified_val = getattr(val, "__name__")
+
+    # Check if the post-checks value is greater than 100 chars in length and use auto id gen if so
+    # isinstance checks can return empty strings which is considered valid, so we explicitly check None on modified_val
+    # for example @pytest.mark.parametrize('x', ('', ' ')) is acceptable
+    if modified_val is None or len(modified_val) > 100:
+        return str(argname) + str(idx)
+    return modified_val
 
 
 def _idvalset(

testing/python/metafunc.py

@@ -286,9 +286,8 @@ def test_unicode_idval(self) -> None:
             ("ação", "a\\xe7\\xe3o"),
             ("josé@blah.com", "jos\\xe9@blah.com"),
             (
-                "δοκ.ιμή@παράδειγμα.δοκιμή",
-                "\\u03b4\\u03bf\\u03ba.\\u03b9\\u03bc\\u03ae@\\u03c0\\u03b1\\u03c1\\u03ac\\u03b4\\u03b5\\u03b9\\u03b3"
-                "\\u03bc\\u03b1.\\u03b4\\u03bf\\u03ba\\u03b9\\u03bc\\u03ae",
+                "δοκ.ιμή@δοκιμή",
+                "\\u03b4\\u03bf\\u03ba.\\u03b9\\u03bc\\u03ae@\\u03b4\\u03bf\\u03ba\\u03b9\\u03bc\\u03ae",
             ),
         ]
         for val, expected in values:
@@ -1899,3 +1898,38 @@ def test_converted_to_str(a, b):
                 "*= 6 passed in *",
             ]
         )
+
+
+def test_auto_generated_long_parametrized_ids(testdir):
+    testdir.makepyfile(
+        """
+    import pytest
+    from datetime import datetime
+    from enum import Enum
+
+    class CustomEnum(Enum):
+        OVER = "over" * 26
+        UNDER = "under" * 2
+
+    @pytest.mark.parametrize(
+    "value, expected",
+    [
+        ("*" * 101, True),
+        (b"*" * 101, True),
+        (25, False),
+        (50.25, False),
+        ("*" * 50, False),
+        (True, False),
+        (datetime(2001, 12, 12), True),
+        (CustomEnum.OVER, False),
+        (datetime, False),
+        (dir, False),
+    ])
+    def test_parametrized_auto_generating_long(request, value, expected):
+        node_name = request.node.name
+        was_rewritten = "value" in node_name
+        assert was_rewritten == expected
+    """
+    )
+    result = testdir.runpytest()
+    result.assert_outcomes(passed=10)