diff --git a/CHANGES.rst b/CHANGES.rst
index fec3e60..345e70f 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -1,3 +1,9 @@
+v3.15.0
+=======
+
+* gh-102209: ``test_implied_dirs_performance`` now tests
+  measures the time complexity experimentally.
+
 v3.14.0
 =======
 
diff --git a/setup.cfg b/setup.cfg
index 313f466..f7832d2 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -46,9 +46,9 @@ testing =
 
 	# local
 	jaraco.itertools
-	func-timeout
 	jaraco.functools
 	more_itertools
+	big-O
 
 docs =
 	# upstream
diff --git a/tests/_context.py b/tests/_context.py
deleted file mode 100644
index 348798a..0000000
--- a/tests/_context.py
+++ /dev/null
@@ -1,30 +0,0 @@
-import contextlib
-import time
-
-
-class DeadlineExceeded(Exception):
-    pass
-
-
-class TimedContext(contextlib.ContextDecorator):
-    """
-    A context that will raise DeadlineExceeded if the
-    max duration is reached during the execution.
-
-    >>> TimedContext(1)(time.sleep)(.1)
-    >>> TimedContext(0)(time.sleep)(.1)
-    Traceback (most recent call last):
-    ...
-    tests._context.DeadlineExceeded: (..., 0)
-    """
-
-    def __init__(self, max_duration: int):
-        self.max_duration = max_duration
-
-    def __enter__(self):
-        self.start = time.monotonic()
-
-    def __exit__(self, *err):
-        duration = time.monotonic() - self.start
-        if duration > self.max_duration:
-            raise DeadlineExceeded(duration, self.max_duration)
diff --git a/tests/_func_timeout_compat.py b/tests/_func_timeout_compat.py
deleted file mode 100644
index b1f2b26..0000000
--- a/tests/_func_timeout_compat.py
+++ /dev/null
@@ -1,8 +0,0 @@
-try:
-    from func_timeout import func_set_timeout as set_timeout
-except ImportError:  # pragma: no cover
-    # provide a fallback that doesn't actually time out
-    from ._context import TimedContext as set_timeout
-
-
-__all__ = ['set_timeout']
diff --git a/tests/_support.py b/tests/_support.py
new file mode 100644
index 0000000..1afdf3b
--- /dev/null
+++ b/tests/_support.py
@@ -0,0 +1,9 @@
+import importlib
+import unittest
+
+
+def import_or_skip(name):
+    try:
+        return importlib.import_module(name)
+    except ImportError:  # pragma: no cover
+        raise unittest.SkipTest(f'Unable to import {name}')
diff --git a/tests/test_complexity.py b/tests/test_complexity.py
new file mode 100644
index 0000000..4021041
--- /dev/null
+++ b/tests/test_complexity.py
@@ -0,0 +1,24 @@
+import unittest
+import string
+
+import zipp
+from jaraco.functools import compose
+from more_itertools import consume
+
+from ._support import import_or_skip
+
+
+big_o = import_or_skip('big_o')
+
+
+class TestComplexity(unittest.TestCase):
+    def test_implied_dirs_performance(self):
+        best, others = big_o.big_o(
+            compose(consume, zipp.CompleteDirs._implied_dirs),
+            lambda size: [
+                '/'.join(string.ascii_lowercase + str(n)) for n in range(size)
+            ],
+            max_n=1000,
+            min_n=1,
+        )
+        assert best <= big_o.complexities.Linear
diff --git a/tests/test_zipp.py b/tests/test_zipp.py
index 9761e11..adebfe2 100644
--- a/tests/test_zipp.py
+++ b/tests/test_zipp.py
@@ -5,19 +5,16 @@
 import tempfile
 import shutil
 import pickle
-import string
 import sys
 import unittest
 import zipfile
 
 import jaraco.itertools
 from jaraco.functools import compose
-from more_itertools import consume
 
 import zipp
 
 from ._test_params import parameterize, Invoked
-from ._func_timeout_compat import set_timeout
 
 
 def add_dirs(zf):
@@ -334,11 +331,6 @@ def test_joinpath_constant_time(self):
         # Check the file iterated all items
         assert entries.count == self.HUGE_ZIPFILE_NUM_ENTRIES
 
-    @set_timeout(3)
-    def test_implied_dirs_performance(self):
-        data = ['/'.join(string.ascii_lowercase + str(n)) for n in range(10000)]
-        consume(zipp.CompleteDirs._implied_dirs(data))
-
     @pass_alpharep
     def test_read_does_not_close(self, alpharep):
         alpharep = self.zipfile_ondisk(alpharep)