Merge pull request #4677 from ianhi/slow-shrink-seed

Liam-DeVoe · web-flow · commit d2a9a599fc0c · 2026-03-24T20:50:47.000-04:00
Print the seed when shrinking is slow
diff --git a/hypothesis-python/RELEASE.rst b/hypothesis-python/RELEASE.rst
@@ -0,0 +1,7 @@
+RELEASE_TYPE: patch
+
+When shrinking takes more than five minutes, Hypothesis now prints the
+``@seed`` decorator alongside the slow-shrinking warning so you can
+reproduce the failure.
+
+Thanks to Ian Hunt-Isaak for this contribution!
diff --git a/hypothesis-python/src/hypothesis/core.py b/hypothesis-python/src/hypothesis/core.py
@@ -2217,19 +2217,37 @@ def wrapped_test(*arguments, **kwargs):
                     generated_seed = (
                         wrapped_test._hypothesis_internal_use_generated_seed
                     )
+                    assert state._runner is not None
+                    stopped_because_slow_shrinking = (
+                        state._runner.statistics.get("stopped-because")
+                        == "shrinking was very slow"
+                    )
                     with local_settings(settings):
-                        if not (state.failed_normally or generated_seed is None):
-                            if running_under_pytest:
-                                report(
-                                    f"You can add @seed({generated_seed}) to this test or "
-                                    f"run pytest with --hypothesis-seed={generated_seed} "
-                                    "to reproduce this failure."
+                        if generated_seed is not None and (
+                            not state.failed_normally or stopped_because_slow_shrinking
+                        ):
+                            pytest_extra_msg = (
+                                (
+                                    ", or by running pytest with "
+                                    f"--hypothesis-seed={generated_seed}"
+                                )
+                                if running_under_pytest
+                                else ""
+                            )
+                            if stopped_because_slow_shrinking:
+                                msg = (
+                                    "\nThis test function exited early because"
+                                    " it took too long to shrink. If desired for debugging, "
+                                    f"you can reproduce this by adding @seed({generated_seed}) "
+                                    f"to this test{pytest_extra_msg}."
                                 )
                             else:
-                                report(
-                                    f"You can add @seed({generated_seed}) to this test to "
-                                    "reproduce this failure."
+                                msg = (
+                                    "You can reproduce this failure by adding "
+                                    f"@seed({generated_seed}) to this test"
+                                    f"{pytest_extra_msg}."
                                 )
+                            report(msg)
                         # The dance here is to avoid showing users long tracebacks
                         # full of Hypothesis internals they don't care about.
                         # We have to do this inline, to avoid adding another
diff --git a/hypothesis-python/src/hypothesis/internal/conjecture/engine.py b/hypothesis-python/src/hypothesis/internal/conjecture/engine.py
@@ -723,7 +723,7 @@ def _backend_cannot_proceed(
                 "WARNING: Hypothesis has spent more than five minutes working to shrink"
                 " a failing example, and stopped because it is making very slow"
                 " progress.  When you re-run your tests, shrinking will resume and may"
-                " take this long before aborting again.\nPLEASE REPORT THIS if you can"
+                " take this long before aborting again.\n\nPLEASE REPORT THIS if you can"
                 " provide a reproducing example, so that we can improve shrinking"
                 " performance for everyone."
             )
diff --git a/hypothesis-python/tests/cover/test_seed_printing.py b/hypothesis-python/tests/cover/test_seed_printing.py
@@ -12,7 +12,15 @@
 
 import pytest
 
-from hypothesis import Verbosity, assume, core, given, settings, strategies as st
+from hypothesis import (
+    HealthCheck,
+    Verbosity,
+    assume,
+    core,
+    given,
+    settings,
+    strategies as st,
+)
 from hypothesis.database import InMemoryExampleDatabase
 from hypothesis.errors import FailedHealthCheck
 
@@ -108,3 +116,26 @@ def test(i):
         test()
 
     assert "@seed" in o.getvalue()
+
+
+@pytest.mark.parametrize("in_pytest", [True, False])
+def test_prints_seed_on_very_slow_shrinking(monkeypatch, in_pytest):
+    monkeypatch.setattr(core, "running_under_pytest", in_pytest)
+
+    @settings(database=None, deadline=None, suppress_health_check=list(HealthCheck))
+    @given(st.integers(min_value=0, max_value=2**64 - 1))
+    def test(n):
+        time.sleep(10)
+        assert n <= 2**33
+
+    with capture_out() as o, pytest.raises(AssertionError):
+        test()
+
+    output = o.getvalue()
+    assert "Hypothesis has spent more than five minutes" in output
+    assert (
+        "This test function exited early because it took too long to shrink" in output
+    )
+    seed = test._hypothesis_internal_use_generated_seed
+    assert output.count(f"@seed({seed})") == 1
+    assert (f"--hypothesis-seed={seed}" in output) == in_pytest

Original file line number	Diff line number	Diff line change
`@@ -723,7 +723,7 @@ def _backend_cannot_proceed(`
`723`	`723`	`"WARNING: Hypothesis has spent more than five minutes working to shrink"`
`724`	`724`	`" a failing example, and stopped because it is making very slow"`
`725`	`725`	`" progress. When you re-run your tests, shrinking will resume and may"`
`726`		`- " take this long before aborting again.\nPLEASE REPORT THIS if you can"`
	`726`	`+ " take this long before aborting again.\n\nPLEASE REPORT THIS if you can"`
`727`	`727`	`" provide a reproducing example, so that we can improve shrinking"`
`728`	`728`	`" performance for everyone."`
`729`	`729`	`)`