Remove TEST_SHARED_FIXTURES (#8965)

I wish it worked, but it's been broken for a long time, so let's admit
defeat and remove it.

The idea of sharing the same pageserver and safekeeper environment
between tests is still sound, and it could save a lot of time in our
CI. We should perhaps put some time into doing that, but we're better
off starting from scratch than trying to make TEST_SHARED_FIXTURES
work in its current form.

test_runner/README.md

@@ -18,8 +18,7 @@ Prerequisites:
 
 Regression tests are in the 'regress' directory. They can be run in
 parallel to minimize total runtime. Most regression test sets up their
-environment with its own pageservers and safekeepers (but see
-`TEST_SHARED_FIXTURES`).
+environment with its own pageservers and safekeepers.
 
 'pg_clients' contains tests for connecting with various client
 libraries. Each client test uses a Dockerfile that pulls an image that
@@ -74,7 +73,6 @@ This is used to construct full path to the postgres binaries.
 Format is 2-digit major version nubmer, i.e. `DEFAULT_PG_VERSION=16`
 `TEST_OUTPUT`: Set the directory where test state and test output files
 should go.
-`TEST_SHARED_FIXTURES`: Try to re-use a single pageserver for all the tests.
 `RUST_LOG`: logging configuration to pass into Neon CLI
 
 Useful parameters and commands:
@@ -259,11 +257,9 @@ compute Postgres nodes. The connections between them can be configured to use JW
 authentication tokens, and some other configuration options can be tweaked too.
 
 The easiest way to get access to a Neon Environment is by using the `neon_simple_env`
-fixture. The 'simple' env may be shared across multiple tests, so don't shut down the nodes
-or make other destructive changes in that environment. Also don't assume that
-there are no tenants or branches or data in the cluster. For convenience, there is a
-branch called `empty`, though. The convention is to create a test-specific branch of
-that and load any test data there, instead of the 'main' branch.
+fixture. For convenience, there is a branch called `empty` in environments created with
+'neon_simple_env'. The convention is to create a test-specific branch of that and load any
+test data there, instead of the 'main' branch.
 
 For more complicated cases, you can build a custom Neon Environment, with the `neon_env`
 fixture:

test_runner/fixtures/neon_fixtures.py

@@ -221,33 +221,6 @@ def neon_api(neon_api_key: str, neon_api_base_url: str) -> NeonAPI:
     return NeonAPI(neon_api_key, neon_api_base_url)
 
 
-def shareable_scope(fixture_name: str, config: Config) -> Literal["session", "function"]:
-    """Return either session of function scope, depending on TEST_SHARED_FIXTURES envvar.
-
-    This function can be used as a scope like this:
-    @pytest.fixture(scope=shareable_scope)
-    def myfixture(...)
-       ...
-    """
-    scope: Literal["session", "function"]
-
-    if os.environ.get("TEST_SHARED_FIXTURES") is None:
-        # Create the environment in the per-test output directory
-        scope = "function"
-    elif (
-        os.environ.get("BUILD_TYPE") is not None
-        and os.environ.get("DEFAULT_PG_VERSION") is not None
-    ):
-        scope = "session"
-    else:
-        pytest.fail(
-            "Shared environment(TEST_SHARED_FIXTURES) requires BUILD_TYPE and DEFAULT_PG_VERSION to be set",
-            pytrace=False,
-        )
-
-    return scope
-
-
 @pytest.fixture(scope="session")
 def worker_port_num():
     return (32768 - BASE_PORT) // int(os.environ.get("PYTEST_XDIST_WORKER_COUNT", "1"))
@@ -1431,8 +1404,8 @@ class NeonEnv:
         return "ep-" + str(self.endpoint_counter)
 
 
-@pytest.fixture(scope=shareable_scope)
-def _shared_simple_env(
+@pytest.fixture(scope="function")
+def neon_simple_env(
     request: FixtureRequest,
     pytestconfig: Config,
     port_distributor: PortDistributor,
@@ -1450,19 +1423,13 @@ def _shared_simple_env(
     pageserver_io_buffer_alignment: Optional[int],
 ) -> Iterator[NeonEnv]:
     """
-    # Internal fixture backing the `neon_simple_env` fixture. If TEST_SHARED_FIXTURES
-     is set, this is shared by all tests using `neon_simple_env`.
+    Simple Neon environment, with no authentication and no safekeepers.
 
     This fixture will use RemoteStorageKind.LOCAL_FS with pageserver.
     """
 
-    if os.environ.get("TEST_SHARED_FIXTURES") is None:
-        # Create the environment in the per-test output directory
-        repo_dir = get_test_repo_dir(request, top_output_dir)
-    else:
-        # We're running shared fixtures. Share a single directory.
-        repo_dir = top_output_dir / "shared_repo"
-        shutil.rmtree(repo_dir, ignore_errors=True)
+    # Create the environment in the per-test output directory
+    repo_dir = get_test_repo_dir(request, top_output_dir)
 
     with NeonEnvBuilder(
         top_output_dir=top_output_dir,
@@ -1489,22 +1456,6 @@ def _shared_simple_env(
 
         yield env
 
-
-@pytest.fixture(scope="function")
-def neon_simple_env(_shared_simple_env: NeonEnv) -> Iterator[NeonEnv]:
-    """
-    Simple Neon environment, with no authentication and no safekeepers.
-
-    If TEST_SHARED_FIXTURES environment variable is set, we reuse the same
-    environment for all tests that use 'neon_simple_env', keeping the
-    page server and safekeepers running. Any compute nodes are stopped after
-    each the test, however.
-    """
-    yield _shared_simple_env
-
-    _shared_simple_env.endpoints.stop_all()
-
-
 @pytest.fixture(scope="function")
 def neon_env_builder(
     pytestconfig: Config,
@@ -4898,14 +4849,7 @@ SMALL_DB_FILE_NAME_REGEX: re.Pattern = re.compile(  # type: ignore[type-arg]
 
 
 # This is autouse, so the test output directory always gets created, even
-# if a test doesn't put anything there. It also solves a problem with the
-# neon_simple_env fixture: if TEST_SHARED_FIXTURES is not set, it
-# creates the repo in the test output directory. But it cannot depend on
-# 'test_output_dir' fixture, because when TEST_SHARED_FIXTURES is not set,
-# it has 'session' scope and cannot access fixtures with 'function'
-# scope. So it uses the get_test_output_dir() function to get the path, and
-# this fixture ensures that the directory exists.  That works because
-# 'autouse' fixtures are run before other fixtures.
+# if a test doesn't put anything there.
 #
 # NB: we request the overlay dir fixture so the fixture does its cleanups
 @pytest.fixture(scope="function", autouse=True)