From 0c6ad49a16f0eb7b6d0a03d73d43803c862e3af5 Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:25 -0700
Subject: [PATCH 1/6] Small refactorings

---
 .../internal/conjecture/shrinker.py           | 53 +++++++------------
 1 file changed, 20 insertions(+), 33 deletions(-)

diff --git a/hypothesis-python/src/hypothesis/internal/conjecture/shrinker.py b/hypothesis-python/src/hypothesis/internal/conjecture/shrinker.py
index 9080d07f63..2ee5d5f4cb 100644
--- a/hypothesis-python/src/hypothesis/internal/conjecture/shrinker.py
+++ b/hypothesis-python/src/hypothesis/internal/conjecture/shrinker.py
@@ -278,8 +278,8 @@ def __init__(self, engine, initial, predicate, allow_transition):
 
         # We keep track of the current best example on the shrink_target
         # attribute.
-        self.shrink_target = None
-        self.update_shrink_target(initial)
+        self.shrink_target = initial
+        self.clear_change_tracking()
         self.shrinks = 0
 
         # We terminate shrinks that seem to have reached their logical
@@ -447,23 +447,15 @@ def s(n):
                     return "s" if n != 1 else ""
 
                 total_deleted = self.initial_size - len(self.shrink_target.buffer)
-
-                self.debug("---------------------")
-                self.debug("Shrink pass profiling")
-                self.debug("---------------------")
-                self.debug("")
                 calls = self.engine.call_count - self.initial_calls
+
                 self.debug(
-                    "Shrinking made a total of %d call%s "
-                    "of which %d shrank. This deleted %d byte%s out of %d."
-                    % (
-                        calls,
-                        s(calls),
-                        self.shrinks,
-                        total_deleted,
-                        s(total_deleted),
-                        self.initial_size,
-                    )
+                    "---------------------\n"
+                    "Shrink pass profiling\n"
+                    "---------------------\n\n"
+                    f"Shrinking made a total of {calls} call{s(calls)} of which "
+                    f"{self.shrinks} shrank. This deleted {total_deleted} bytes out "
+                    f"of {self.initial_size}."
                 )
                 for useful in [True, False]:
                     self.debug("")
@@ -828,22 +820,17 @@ def __changed_blocks(self):
 
     def update_shrink_target(self, new_target):
         assert isinstance(new_target, ConjectureResult)
-        if self.shrink_target is not None:
-            self.shrinks += 1
-            # If we are just taking a long time to shrink we don't want to
-            # trigger this heuristic, so whenever we shrink successfully
-            # we give ourselves a bit of breathing room to make sure we
-            # would find a shrink that took that long to find the next time.
-            # The case where we're taking a long time but making steady
-            # progress is handled by `finish_shrinking_deadline` in engine.py
-            self.max_stall = max(
-                self.max_stall, (self.calls - self.calls_at_last_shrink) * 2
-            )
-            self.calls_at_last_shrink = self.calls
-        else:
-            self.__all_changed_blocks = set()
-            self.__last_checked_changed_at = new_target
-
+        self.shrinks += 1
+        # If we are just taking a long time to shrink we don't want to
+        # trigger this heuristic, so whenever we shrink successfully
+        # we give ourselves a bit of breathing room to make sure we
+        # would find a shrink that took that long to find the next time.
+        # The case where we're taking a long time but making steady
+        # progress is handled by `finish_shrinking_deadline` in engine.py
+        self.max_stall = max(
+            self.max_stall, (self.calls - self.calls_at_last_shrink) * 2
+        )
+        self.calls_at_last_shrink = self.calls
         self.shrink_target = new_target
         self.__derived_values = {}
 

From 233a6284ea2718ed3890dc26fadadb1baef5a98f Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:25 -0700
Subject: [PATCH 2/6] Remove dead code

This never actually worked, because the __module__ string doesn't have a __name__ attribute.  Since we want DB keys to be independent of the file anyway, we'll just delete the clause.
---
 hypothesis-python/src/hypothesis/internal/reflection.py | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/hypothesis-python/src/hypothesis/internal/reflection.py b/hypothesis-python/src/hypothesis/internal/reflection.py
index b758a8ef20..736d4ede9e 100644
--- a/hypothesis-python/src/hypothesis/internal/reflection.py
+++ b/hypothesis-python/src/hypothesis/internal/reflection.py
@@ -64,10 +64,6 @@ def function_digest(function):
         hasher.update(function.__name__.encode())
     except AttributeError:
         pass
-    try:
-        hasher.update(function.__module__.__name__.encode())
-    except AttributeError:
-        pass
     try:
         # We prefer to use the modern signature API, but left this for compatibility.
         # While we don't promise stability of the database, there's no advantage to

From 7c56922991a700bad02a58c5aed1972439de6132 Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:25 -0700
Subject: [PATCH 3/6] Fix ParamSpec for typecheckers

Co-Authored-By: Shantanu <12621235+hauntsaninja@users.noreply.github.com>
---
 .../src/hypothesis/internal/compat.py           | 13 +++++++++++++
 .../src/hypothesis/strategies/_internal/core.py | 17 ++++++++---------
 .../tests/nocover/test_type_lookup.py           |  7 +++----
 .../typing_extensions/test_backported_types.py  |  2 +-
 4 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/hypothesis-python/src/hypothesis/internal/compat.py b/hypothesis-python/src/hypothesis/internal/compat.py
index 67297bcdaa..e7e3bf2a53 100644
--- a/hypothesis-python/src/hypothesis/internal/compat.py
+++ b/hypothesis-python/src/hypothesis/internal/compat.py
@@ -22,6 +22,19 @@
         BaseExceptionGroup as BaseExceptionGroup,
         ExceptionGroup as ExceptionGroup,
     )
+if typing.TYPE_CHECKING:  # pragma: no cover
+    from typing_extensions import Concatenate as Concatenate, ParamSpec as ParamSpec
+else:
+    try:
+        from typing import Concatenate as Concatenate, ParamSpec as ParamSpec
+    except ImportError:
+        try:
+            from typing_extensions import (
+                Concatenate as Concatenate,
+                ParamSpec as ParamSpec,
+            )
+        except ImportError:
+            Concatenate, ParamSpec = None, None
 
 PYPY = platform.python_implementation() == "PyPy"
 WINDOWS = platform.system() == "Windows"
diff --git a/hypothesis-python/src/hypothesis/strategies/_internal/core.py b/hypothesis-python/src/hypothesis/strategies/_internal/core.py
index 3c0eadc7b5..c122985fb9 100644
--- a/hypothesis-python/src/hypothesis/strategies/_internal/core.py
+++ b/hypothesis-python/src/hypothesis/strategies/_internal/core.py
@@ -49,7 +49,14 @@
 from hypothesis.errors import InvalidArgument, ResolutionFailed
 from hypothesis.internal.cathetus import cathetus
 from hypothesis.internal.charmap import as_general_categories
-from hypothesis.internal.compat import ceil, floor, get_type_hints, is_typed_named_tuple
+from hypothesis.internal.compat import (
+    Concatenate,
+    ParamSpec,
+    ceil,
+    floor,
+    get_type_hints,
+    is_typed_named_tuple,
+)
 from hypothesis.internal.conjecture.utils import (
     calc_label_from_cls,
     check_sample,
@@ -122,14 +129,6 @@
 except ImportError:  # < py3.8
     Protocol = object  # type: ignore[assignment]
 
-try:
-    from typing import Concatenate, ParamSpec
-except ImportError:
-    try:
-        from typing_extensions import Concatenate, ParamSpec
-    except ImportError:
-        ParamSpec = None  # type: ignore
-
 
 @cacheable
 @defines_strategy()
diff --git a/hypothesis-python/tests/nocover/test_type_lookup.py b/hypothesis-python/tests/nocover/test_type_lookup.py
index 038d454870..b5c2bfbd04 100644
--- a/hypothesis-python/tests/nocover/test_type_lookup.py
+++ b/hypothesis-python/tests/nocover/test_type_lookup.py
@@ -14,14 +14,13 @@
 
 from hypothesis import strategies as st
 from hypothesis.errors import InvalidArgument
+from hypothesis.internal.compat import Concatenate, ParamSpec
 from hypothesis.strategies._internal.types import NON_RUNTIME_TYPES
 
 try:
-    from typing import Concatenate, ParamSpec, TypeGuard  # new in 3.10
+    from typing import TypeGuard  # new in 3.10
 except ImportError:
-    Concatenate = ParamSpec = TypeGuard = None
-
-# See also typing_extensions/test_backported_types.py
+    TypeGuard = None
 
 
 @pytest.mark.parametrize("non_runtime_type", NON_RUNTIME_TYPES)
diff --git a/hypothesis-python/tests/typing_extensions/test_backported_types.py b/hypothesis-python/tests/typing_extensions/test_backported_types.py
index 61f59b0565..a6f3512de0 100644
--- a/hypothesis-python/tests/typing_extensions/test_backported_types.py
+++ b/hypothesis-python/tests/typing_extensions/test_backported_types.py
@@ -31,7 +31,7 @@
 
 from tests.common.debug import assert_all_examples, find_any
 
-# See also nocover/test_type_lookp.py
+# See also nocover/test_type_lookup.py
 
 
 @pytest.mark.parametrize("value", ["dog", b"goldfish", 42, 63.4, -80.5, False])

From fa23c23335197cff3b9da2b7e80d8815db319e5c Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:26 -0700
Subject: [PATCH 4/6] Drop some old warnings config

---
 hypothesis-python/tests/common/setup.py | 13 +------------
 1 file changed, 1 insertion(+), 12 deletions(-)

diff --git a/hypothesis-python/tests/common/setup.py b/hypothesis-python/tests/common/setup.py
index 25c37ef253..f1a36994c9 100644
--- a/hypothesis-python/tests/common/setup.py
+++ b/hypothesis-python/tests/common/setup.py
@@ -25,10 +25,7 @@ def run():
     filterwarnings("ignore", category=ImportWarning)
     filterwarnings("ignore", category=FutureWarning, module="pandas._version")
 
-    # Fixed in recent versions but allowed by pytest=3.0.0; see #1630
-    filterwarnings("ignore", category=DeprecationWarning, module="pluggy")
-
-    # See https://github.com/numpy/numpy/pull/432
+    # See https://github.com/numpy/numpy/pull/432; still a thing as of 2022.
     filterwarnings("ignore", message="numpy.dtype size changed")
     filterwarnings("ignore", message="numpy.ufunc size changed")
 
@@ -42,14 +39,6 @@ def run():
         category=UserWarning,
     )
 
-    # Imported by Pandas in version 1.9, but fixed in later versions.
-    filterwarnings(
-        "ignore", message="Importing from numpy.testing.decorators is deprecated"
-    )
-    filterwarnings(
-        "ignore", message="Importing from numpy.testing.nosetester is deprecated"
-    )
-
     # User-facing warning which does not apply to our own tests
     filterwarnings("ignore", category=NonInteractiveExampleWarning)
 

From fb0855de3dacdf7bf8b2e1c61881002fb6dc64fa Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:26 -0700
Subject: [PATCH 5/6] Dogfooding the explain phase

---
 hypothesis-python/tests/common/setup.py        | 8 ++++++--
 hypothesis-python/tests/cover/test_phases.py   | 3 ++-
 hypothesis-python/tests/cover/test_settings.py | 2 +-
 3 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/hypothesis-python/tests/common/setup.py b/hypothesis-python/tests/common/setup.py
index f1a36994c9..d109273199 100644
--- a/hypothesis-python/tests/common/setup.py
+++ b/hypothesis-python/tests/common/setup.py
@@ -12,7 +12,7 @@
 from tempfile import mkdtemp
 from warnings import filterwarnings
 
-from hypothesis import Verbosity, settings
+from hypothesis import Phase, Verbosity, settings
 from hypothesis._settings import not_set
 from hypothesis.configuration import set_hypothesis_home_dir
 from hypothesis.errors import NonInteractiveExampleWarning
@@ -66,7 +66,11 @@ def run():
             )
 
     settings.register_profile(
-        "default", settings(max_examples=20 if IN_COVERAGE_TESTS else not_set)
+        "default",
+        settings(
+            max_examples=20 if IN_COVERAGE_TESTS else not_set,
+            phases=list(Phase),  # Dogfooding the explain phase
+        ),
     )
 
     settings.register_profile("speedy", settings(max_examples=5))
diff --git a/hypothesis-python/tests/cover/test_phases.py b/hypothesis-python/tests/cover/test_phases.py
index ca1e9b2b9d..8ccca601ed 100644
--- a/hypothesis-python/tests/cover/test_phases.py
+++ b/hypothesis-python/tests/cover/test_phases.py
@@ -11,6 +11,7 @@
 import pytest
 
 from hypothesis import Phase, example, given, settings, strategies as st
+from hypothesis._settings import all_settings
 from hypothesis.database import ExampleDatabase, InMemoryExampleDatabase
 from hypothesis.errors import InvalidArgument
 
@@ -47,7 +48,7 @@ def test_sorts_and_dedupes_phases(arg, expected):
 
 
 def test_phases_default_to_all_except_explain():
-    assert settings().phases + (Phase.explain,) == tuple(Phase)
+    assert all_settings["phases"].default + (Phase.explain,) == tuple(Phase)
 
 
 def test_does_not_reuse_saved_examples_if_reuse_not_in_phases():
diff --git a/hypothesis-python/tests/cover/test_settings.py b/hypothesis-python/tests/cover/test_settings.py
index 19914c42cb..e3ca7376ce 100644
--- a/hypothesis-python/tests/cover/test_settings.py
+++ b/hypothesis-python/tests/cover/test_settings.py
@@ -464,7 +464,7 @@ def __repr__(self):
 
 
 def test_show_changed():
-    s = settings(max_examples=999, database=None)
+    s = settings(max_examples=999, database=None, phases=tuple(Phase)[:-1])
     assert s.show_changed() == "database=None, max_examples=999"
 
 

From 90c4b7bc4764fc39257ee468014a513231b07279 Mon Sep 17 00:00:00 2001
From: Zac Hatfield-Dodds <zac.hatfield.dodds@gmail.com>
Date: Sat, 20 Aug 2022 09:00:26 -0700
Subject: [PATCH 6/6] Skip known-uninformative locations

---
 hypothesis-python/RELEASE.rst                 |  5 ++
 hypothesis-python/src/hypothesis/core.py      |  3 +-
 .../src/hypothesis/internal/scrutineer.py     | 32 ++++++++++---
 .../tests/cover/test_scrutineer.py            | 46 -------------------
 .../tests/cover/test_stateful.py              | 23 +++++++---
 .../tests/nocover/test_scrutineer.py          | 22 +++++++++
 6 files changed, 69 insertions(+), 62 deletions(-)
 create mode 100644 hypothesis-python/RELEASE.rst
 delete mode 100644 hypothesis-python/tests/cover/test_scrutineer.py

diff --git a/hypothesis-python/RELEASE.rst b/hypothesis-python/RELEASE.rst
new file mode 100644
index 0000000000..75347a5ebc
--- /dev/null
+++ b/hypothesis-python/RELEASE.rst
@@ -0,0 +1,5 @@
+RELEASE_TYPE: patch
+
+This patch fixes some type annotations for Python 3.9 and earlier (:issue:`3397`),
+and teaches :ref:`explain mode <phases>` about certain locations it should not
+bother reporting (:issue:`3439`).
diff --git a/hypothesis-python/src/hypothesis/core.py b/hypothesis-python/src/hypothesis/core.py
index 14ade3fbb1..87af19d789 100644
--- a/hypothesis-python/src/hypothesis/core.py
+++ b/hypothesis-python/src/hypothesis/core.py
@@ -881,8 +881,7 @@ def run_engine(self):
                 errors_to_report.append((fragments, err))
             except BaseException as e:
                 # If we have anything for explain-mode, this is the time to report.
-                for line in explanations[falsifying_example.interesting_origin]:
-                    fragments.append(line)
+                fragments.extend(explanations[falsifying_example.interesting_origin])
                 errors_to_report.append(
                     (fragments, e.with_traceback(get_trimmed_traceback()))
                 )
diff --git a/hypothesis-python/src/hypothesis/internal/scrutineer.py b/hypothesis-python/src/hypothesis/internal/scrutineer.py
index 0a63508699..3071111f6a 100644
--- a/hypothesis-python/src/hypothesis/internal/scrutineer.py
+++ b/hypothesis-python/src/hypothesis/internal/scrutineer.py
@@ -12,6 +12,7 @@
 from collections import defaultdict
 from functools import lru_cache, reduce
 from itertools import groupby
+from os import sep
 from pathlib import Path
 
 from hypothesis._settings import Phase, Verbosity
@@ -45,6 +46,20 @@ def trace(self, frame, event, arg):
                 self._previous_location = current_location
 
 
+UNHELPFUL_LOCATIONS = (
+    # There's a branch which is only taken when an exception is active while exiting
+    # a contextmanager; this is probably after the fault has been triggered.
+    # Similar reasoning applies to a few other standard-library modules: even
+    # if the fault was later, these still aren't useful locations to report!
+    f"{sep}contextlib.py",
+    f"{sep}inspect.py",
+    f"{sep}re.py",
+    f"{sep}re{sep}__init__.py",  # refactored in Python 3.11
+    # Quite rarely, the first AFNP line is in Pytest's assertion-rewriting module.
+    f"{sep}_pytest{sep}assertion{sep}rewrite.py",
+)
+
+
 def get_explaining_locations(traces):
     # Traces is a dict[interesting_origin | None, set[frozenset[tuple[str, int]]]]
     # Each trace in the set might later become a Counter instead of frozenset.
@@ -84,7 +99,13 @@ def get_explaining_locations(traces):
             else:
                 queue.update(cf_graphs[origin][src] - seen)
 
-    return explanations
+    # The last step is to filter out explanations that we know would be uninformative.
+    # When this is the first AFNP location, we conclude that Scrutineer missed the
+    # real divergence (earlier in the trace) and drop that unhelpful explanation.
+    return {
+        origin: {loc for loc in afnp_locs if not loc[0].endswith(UNHELPFUL_LOCATIONS)}
+        for origin, afnp_locs in explanations.items()
+    }
 
 
 LIB_DIR = str(Path(sys.executable).parent / "lib")
@@ -92,13 +113,11 @@ def get_explaining_locations(traces):
     "Explanation:",
     "    These lines were always and only run by failing examples:",
 )
-HAD_TRACE = "    We didn't try to explain this, because sys.gettrace()="
 
 
 def make_report(explanations, cap_lines_at=5):
     report = defaultdict(list)
     for origin, locations in explanations.items():
-        assert locations  # or else we wouldn't have stored the key, above.
         report_lines = [
             "        {}:{}".format(k, ", ".join(map(str, sorted(l for _, l in v))))
             for k, v in groupby(locations, lambda kv: kv[0])
@@ -107,15 +126,14 @@ def make_report(explanations, cap_lines_at=5):
         if len(report_lines) > cap_lines_at + 1:
             msg = "        (and {} more with settings.verbosity >= verbose)"
             report_lines[cap_lines_at:] = [msg.format(len(report_lines[cap_lines_at:]))]
-        report[origin] = list(EXPLANATION_STUB) + report_lines
+        if report_lines:  # We might have filtered out every location as uninformative.
+            report[origin] = list(EXPLANATION_STUB) + report_lines
     return report
 
 
 def explanatory_lines(traces, settings):
     if Phase.explain in settings.phases and sys.gettrace() and not traces:
-        return defaultdict(
-            lambda: [EXPLANATION_STUB[0], HAD_TRACE + repr(sys.gettrace())]
-        )
+        return defaultdict(list)
     # Return human-readable report lines summarising the traces
     explanations = get_explaining_locations(traces)
     max_lines = 5 if settings.verbosity <= Verbosity.normal else 100
diff --git a/hypothesis-python/tests/cover/test_scrutineer.py b/hypothesis-python/tests/cover/test_scrutineer.py
deleted file mode 100644
index f2cfe2bd0d..0000000000
--- a/hypothesis-python/tests/cover/test_scrutineer.py
+++ /dev/null
@@ -1,46 +0,0 @@
-# This file is part of Hypothesis, which may be found at
-# https://github.com/HypothesisWorks/hypothesis/
-#
-# Copyright the Hypothesis Authors.
-# Individual contributors are listed in AUTHORS.rst and the git log.
-#
-# This Source Code Form is subject to the terms of the Mozilla Public License,
-# v. 2.0. If a copy of the MPL was not distributed with this file, You can
-# obtain one at https://mozilla.org/MPL/2.0/.
-
-import re
-import sys
-
-import pytest
-
-from hypothesis.internal.compat import PYPY
-from hypothesis.internal.scrutineer import HAD_TRACE
-
-CODE_SAMPLE = """
-from hypothesis import Phase, given, settings, strategies as st
-
-@settings(phases=tuple(Phase), derandomize=True)
-@given(st.integers())
-def test_reports_branch_in_test(x):
-    if x > 10:
-        raise AssertionError  # BUG
-"""
-
-
-@pytest.mark.skipif(PYPY, reason="Tracing is slow under PyPy")
-def test_cannot_explain_message(testdir):
-    # Most of the explanation-related code can't be run under coverage, but
-    # what we can cover is the code that prints a message when the explanation
-    # tracer couldn't be installed.
-
-    no_tracer = sys.gettrace() is None
-    try:
-        if no_tracer:
-            sys.settrace(lambda frame, event, arg: None)
-        test_file = testdir.makepyfile(CODE_SAMPLE)
-        testdir.runpytest_inprocess(test_file, "--tb=native").stdout.re_match_lines(
-            [r"Explanation:", re.escape(HAD_TRACE)], consecutive=True
-        )
-    finally:
-        if no_tracer:
-            sys.settrace(None)
diff --git a/hypothesis-python/tests/cover/test_stateful.py b/hypothesis-python/tests/cover/test_stateful.py
index dbbb911f9e..ce6f60b55c 100644
--- a/hypothesis-python/tests/cover/test_stateful.py
+++ b/hypothesis-python/tests/cover/test_stateful.py
@@ -9,6 +9,7 @@
 # obtain one at https://mozilla.org/MPL/2.0/.
 
 import base64
+import sys
 from collections import defaultdict
 
 import pytest
@@ -19,6 +20,7 @@
 from hypothesis.control import current_build_context
 from hypothesis.database import ExampleDatabase
 from hypothesis.errors import DidNotReproduce, Flaky, InvalidArgument, InvalidDefinition
+from hypothesis.internal.compat import PYPY
 from hypothesis.internal.entropy import deterministic_PRNG
 from hypothesis.stateful import (
     Bundle,
@@ -676,10 +678,7 @@ def rule_1(self):
     with pytest.raises(ValueError) as err:
         run_state_machine_as_test(BadRuleWithGoodInvariants)
 
-    result = "\n".join(err.value.__notes__)
-    assert (
-        result
-        == """
+    expected = """\
 Falsifying example:
 state = BadRuleWithGoodInvariants()
 state.invariant_1()
@@ -691,9 +690,19 @@ def rule_1(self):
 state.invariant_2()
 state.invariant_3()
 state.rule_1()
-state.teardown()
-""".strip()
-    )
+state.teardown()"""
+
+    if PYPY or sys.gettrace():  # explain mode disabled in these cases
+        result = "\n".join(err.value.__notes__)
+    else:
+        # Non-PyPy runs include explain mode, but we skip the final line because
+        # it includes the absolute path, which of course varies between machines.
+        expected += """
+Explanation:
+    These lines were always and only run by failing examples:"""
+        result = "\n".join(err.value.__notes__[:-1])
+
+    assert expected == result
 
 
 def test_always_runs_at_least_one_step():
diff --git a/hypothesis-python/tests/nocover/test_scrutineer.py b/hypothesis-python/tests/nocover/test_scrutineer.py
index b24033a170..b0050320e7 100644
--- a/hypothesis-python/tests/nocover/test_scrutineer.py
+++ b/hypothesis-python/tests/nocover/test_scrutineer.py
@@ -79,3 +79,25 @@ def test_no_explanations_if_deadline_exceeded(code, testdir):
     code = code.replace("AssertionError", "DeadlineExceeded(timedelta(), timedelta())")
     pytest_stdout, _ = get_reports(DEADLINE_PRELUDE + PRELUDE + code, testdir=testdir)
     assert "Explanation:" not in pytest_stdout
+
+
+NO_SHOW_CONTEXTLIB = """
+from contextlib import contextmanager
+from hypothesis import given, strategies as st, Phase, settings
+
+@contextmanager
+def ctx():
+    yield
+
+@settings(phases=list(Phase))
+@given(st.integers())
+def test(x):
+    with ctx():
+        assert x < 100
+"""
+
+
+@pytest.mark.skipif(PYPY, reason="Tracing is slow under PyPy")
+def test_skips_uninformative_locations(testdir):
+    pytest_stdout, _ = get_reports(NO_SHOW_CONTEXTLIB, testdir=testdir)
+    assert "Explanation:" not in pytest_stdout