Fix passenv CI in tox ini and make tests insensitive to the presence of the CI env variable (#13684)

As discussed in #13684.

---------

Co-authored-by: 🇺🇦 Sviatoslav Sydorenko (Святослав Сидоренко) <[email protected]>

Author: ogrisel

changelog/13684.contrib.rst

@@ -0,0 +1 @@
+Make pytest's own testsuite insensitive to the presence of the ``CI`` environment variable -- by :user:`ogrisel`.

pyproject.toml

@@ -428,6 +428,9 @@ markers = [
     "slow",
     # experimental mark for all tests using pexpect
     "uses_pexpect",
+    # Disables the `remove_ci_env_var` autouse fixture on a given test that
+    # actually inspects whether the CI environment variable is set.
+    "keep_ci_var",
 ]
 
 [tool.towncrier]

testing/conftest.py

@@ -237,3 +237,15 @@ def mock_timing(monkeypatch: MonkeyPatch):
     result = MockTiming()
     result.patch(monkeypatch)
     return result
+
+
+@pytest.fixture(autouse=True)
+def remove_ci_env_var(monkeypatch: MonkeyPatch, request: pytest.FixtureRequest) -> None:
+    """Make the test insensitive if it is running in CI or not.
+
+    Use `@pytest.mark.keep_ci_var` in a test to avoid applying this fixture, letting the test
+    see the real `CI` variable (if present).
+    """
+    has_keep_ci_mark = request.node.get_closest_marker("keep_ci_var") is not None
+    if not has_keep_ci_mark:
+        monkeypatch.delenv("CI", raising=False)

testing/python/approx.py

@@ -1085,10 +1085,10 @@ def test_map_over_nested_lists(self):
         ]
 
     def test_map_over_mixed_sequence(self):
-        assert _recursive_sequence_map(sqrt, [4, (25, 64), [(49)]]) == [
+        assert _recursive_sequence_map(sqrt, [4, (25, 64), [49]]) == [
             2,
             (5, 8),
-            [(7)],
+            [7],
         ]
 
     def test_map_over_sequence_like(self):

testing/test_faulthandler.py

@@ -71,6 +71,7 @@ def test_disabled():
     assert result.ret == 0
 
 
+@pytest.mark.keep_ci_var
 @pytest.mark.parametrize(
     "enabled",
     [

tox.ini

@@ -52,6 +52,7 @@ passenv =
     PYTEST_ADDOPTS
     TERM
     SETUPTOOLS_SCM_PRETEND_VERSION_FOR_PYTEST
+    CI
 setenv =
     _PYTEST_TOX_DEFAULT_POSARGS={env:_PYTEST_TOX_POSARGS_DOCTESTING:} {env:_PYTEST_TOX_POSARGS_LSOF:} {env:_PYTEST_TOX_POSARGS_XDIST:} {env:_PYTEST_FILES:}