Automatically reload settings profile if it's redefined

hypothesis-python/RELEASE.rst

@@ -0,0 +1,5 @@
+RELEASE_TYPE: minor
+
+This changes the behaviour of settings profiles so that if you reregister the currently loaded profile it will automatically reload it. Previously you would have had to load it again.
+
+In particular this means that if you register a "ci" profile, it will automatically be used when Hypothesis detects you are running on CI.

hypothesis-python/docs/settings.rst

@@ -251,13 +251,27 @@ by your conftest you can load one with the command line option ``--hypothesis-pr
 
 
 Hypothesis comes with two built-in profiles, ``ci`` and ``default``.
-``ci`` is set up to have good defaults for running in a CI environment, so emphasizes determinism, while the 
+``ci`` is set up to have good defaults for running in a CI environment, so emphasizes determinism, while the
 ``default`` settings are picked to be more likely to find bugs and to have a good workflow when used for local development.
 
-Hypothesis will automatically detect certain common CI environments and use the CI profile automatically
+Hypothesis will automatically detect certain common CI environments and use the ci profile automatically
 when running in them.
 In particular, if you wish to use the ``ci`` profile, setting the ``CI`` environment variable will do this.
 
+This will still be the case if you register your own ci profile. For example, if you wanted to run more examples in CI, you might configure it as follows:
+
+.. code-block:: python
+
+    settings.register_profile(
+        "ci",
+        settings(
+            settings.get_profile("ci"),
+            max_examples=1000,
+        ),
+    )
+
+This will configure your CI to run 1000 examples per test rather than the default of 100, and this change will automatically be picked up when running on a CI server.
+
 .. _healthchecks:
 
 -------------

hypothesis-python/src/hypothesis/_settings.py

@@ -97,7 +97,7 @@ def default(cls):
         v = default_variable.value
         if v is not None:
             return v
-        if hasattr(settings, "_current_profile"):
+        if getattr(settings, "_current_profile", None) is not None:
             settings.load_profile(settings._current_profile)
             assert default_variable.value is not None
         return default_variable.value
@@ -132,6 +132,7 @@ class settings(metaclass=settingsMeta):
     __definitions_are_locked = False
     _profiles: ClassVar[dict[str, "settings"]] = {}
     __module__ = "hypothesis"
+    _current_profile = None
 
     def __getattr__(self, name):
         if name in all_settings:
@@ -316,9 +317,15 @@ def register_profile(
         :class:`~hypothesis.settings`: optional ``parent`` settings, and
         keyword arguments for each setting that will be set differently to
         parent (or settings.default, if parent is None).
+
+        If you register a profile that has already been defined and that profile
+        is the currently loaded profile, the new changes will take effect immediately,
+        and do not require reloading the profile.
         """
         check_type(str, name, "name")
         settings._profiles[name] = settings(parent=parent, **kwargs)
+        if settings._current_profile == name:
+            settings.load_profile(name)
 
     @staticmethod
     def get_profile(name: str) -> "settings":
@@ -767,8 +774,7 @@ def note_deprecation(
 settings.register_profile("ci", CI)
 
 
-# This is tested in a subprocess so the branch doesn't show up in coverage.
-if is_in_ci():  # pragma: no cover
+if is_in_ci():
     settings.load_profile("ci")
 
 assert settings.default is not None

hypothesis-python/tests/cover/test_settings.py

@@ -558,3 +558,40 @@ def test_check_defaults_to_randomize_when_not_running_on_ci():
         ).strip()
         == "False"
     )
+
+
+def test_reloads_the_loaded_profile_if_registered_again():
+    prev_profile = settings._current_profile
+    try:
+        test_profile = "some nonsense profile purely for this test"
+        test_value = 123456
+        settings.register_profile(test_profile, settings(max_examples=test_value))
+        settings.load_profile(test_profile)
+        assert settings.default.max_examples == test_value
+        test_value_2 = 42
+        settings.register_profile(test_profile, settings(max_examples=test_value_2))
+        assert settings.default.max_examples == test_value_2
+    finally:
+        if prev_profile is not None:
+            settings.load_profile(prev_profile)
+
+
+CI_TESTING_SCRIPT = """
+from hypothesis import settings
+
+if __name__ == '__main__':
+    settings.register_profile("ci", settings(max_examples=42))
+    assert settings.default.max_examples == 42
+"""
+
+
+@skipif_emscripten
+def test_will_automatically_pick_up_changes_to_ci_profile_in_ci():
+    env = dict(os.environ)
+    env["CI"] = "true"
+    subprocess.check_call(
+        [sys.executable, "-c", CI_TESTING_SCRIPT],
+        env=env,
+        text=True,
+        encoding="utf-8",
+    )