tests: support for running on single pg version, use in one place (#6525)

Some tests which are unit test alike do not need to run on different pg
versions. Logging test is one of them which I found for unrelated
reasons.

Co-authored-by: Alexander Bayandin <alexander@neon.tech>

test_runner/fixtures/pg_version.py

@@ -52,7 +52,7 @@ class PgVersion(str, enum.Enum):
         return None
 
 
-DEFAULT_VERSION: PgVersion = PgVersion.V14
+DEFAULT_VERSION: PgVersion = PgVersion.V15
 
 
 def skip_on_postgres(version: PgVersion, reason: str):
@@ -78,6 +78,13 @@ def pytest_addoption(parser: Parser):
     )
 
 
+def run_only_on_default_postgres(reason: str):
+    return pytest.mark.skipif(
+        PgVersion(os.environ.get("DEFAULT_PG_VERSION", DEFAULT_VERSION)) is not DEFAULT_VERSION,
+        reason=reason,
+    )
+
+
 def pytest_configure(config: Config):
     if config.getoption("--pg-version"):
         raise Exception("--pg-version is deprecated, use DEFAULT_PG_VERSION env var instead")

test_runner/regress/test_logging.py

@@ -3,10 +3,12 @@ import uuid
 import pytest
 from fixtures.log_helper import log
 from fixtures.neon_fixtures import NeonEnvBuilder
+from fixtures.pg_version import run_only_on_default_postgres
 from fixtures.utils import wait_until
 
 
 @pytest.mark.parametrize("level", ["trace", "debug", "info", "warn", "error"])
+@run_only_on_default_postgres("it does not use any postgres functionality")
 def test_logging_event_count(neon_env_builder: NeonEnvBuilder, level: str):
     # self-test: make sure the event is logged (i.e., our testing endpoint works)
     log_expected = {