Pytest auto-close plugin for Datasette instances

Installs a pytest11 entry point so that every Datasette() constructed
inside a pytest_runtest_call phase is auto-closed at the end of the test.
Fixture-scoped instances are untouched. Opt out via the
datasette_autoclose = false ini option.

This gives large test suites a safety net against FD exhaustion and leaked
write threads from the now-default temp-disk internal database without
requiring every existing test to be rewritten.

Refs #2692

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/test_pytest_autoclose_plugin.py

@@ -0,0 +1,93 @@
+"""
+Tests for datasette._pytest_plugin — the pytest plugin that auto-closes
+Datasette instances constructed inside test bodies.
+
+These tests drive a real pytest session in a subprocess so the plugin
+operates exactly as it would for a downstream consumer.
+"""
+
+import subprocess
+import sys
+import textwrap
+from pathlib import Path
+
+import pytest
+
+REPO_ROOT = Path(__file__).parent.parent
+
+
+def _run_pytest(tmp_path: Path) -> subprocess.CompletedProcess:
+    return subprocess.run(
+        [sys.executable, "-m", "pytest", "-v", str(tmp_path)],
+        cwd=str(tmp_path),
+        capture_output=True,
+        text=True,
+    )
+
+
+def test_auto_close_of_instances_made_in_test_body(tmp_path):
+    # Two ordered tests:
+    #   test_a makes a Datasette() and stashes a hard reference
+    #   test_b asserts that the hard-reffed instance was closed by the plugin
+    (tmp_path / "test_sample.py").write_text(textwrap.dedent("""
+            from datasette.app import Datasette
+
+            _stash = {}
+
+            def test_a():
+                ds = Datasette(memory=True)
+                _stash["ds"] = ds
+                assert ds._closed is False
+
+            def test_b():
+                assert _stash["ds"]._closed is True
+            """))
+    result = _run_pytest(tmp_path)
+    assert result.returncode == 0, result.stdout + result.stderr
+
+
+def test_fixture_scoped_instance_is_not_closed(tmp_path):
+    # A module-scoped fixture instance must survive across tests in the module.
+    (tmp_path / "test_fixture.py").write_text(textwrap.dedent("""
+            import pytest
+            from datasette.app import Datasette
+
+            @pytest.fixture(scope="module")
+            def ds():
+                return Datasette(memory=True)
+
+            def test_first(ds):
+                assert ds._closed is False
+
+            def test_second(ds):
+                # Still alive because the plugin only tracks instances
+                # constructed during pytest_runtest_call, not during fixture
+                # setup.
+                assert ds._closed is False
+            """))
+    result = _run_pytest(tmp_path)
+    assert result.returncode == 0, result.stdout + result.stderr
+
+
+def test_opt_out_via_ini(tmp_path):
+    # datasette_autoclose = false should leave instances untouched.
+    (tmp_path / "pytest.ini").write_text(textwrap.dedent("""
+            [pytest]
+            datasette_autoclose = false
+            """).strip())
+    (tmp_path / "test_optout.py").write_text(textwrap.dedent("""
+            from datasette.app import Datasette
+
+            _stash = {}
+
+            def test_a():
+                ds = Datasette(memory=True)
+                _stash["ds"] = ds
+
+            def test_b():
+                # Opt-out: plugin must not have closed it.
+                assert _stash["ds"]._closed is False
+                _stash["ds"].close()
+            """))
+    result = _run_pytest(tmp_path)
+    assert result.returncode == 0, result.stdout + result.stderr