fix(app): avoid reconfiguring root logging in test runs to preserve caplog

documentation/changelog.rst

@@ -56,6 +56,7 @@ Bugfixes
 * The time range sent when loading an asset's KPIs was off by the viewer's UTC offset, so KPIs could cover the wrong days [see `PR #2435 <https://www.github.com/FlexMeasures/flexmeasures/pull/2435>`_]
 * An asset's status page showed only some of the sensors it reported on, in an order that changed between reloads, and it reported on fixed quantities from the flex-context, which have no data to be up to date with [see `PR #2489 <https://www.github.com/FlexMeasures/flexmeasures/pull/2489>`_]
 * Saving an asset chart as PNG or SVG drew the legend over the graph whenever it listed more sensors than fit beside a subplot; the exported image now makes room for every entry beside its own plot, without shrinking the plot, and spells out the sensor names that the on-screen legend abbreviates [see `PR #2517 <https://www.github.com/FlexMeasures/flexmeasures/pull/2517>`_]
+* Building a custom application in a test or with ``do_configure_logging=False`` no longer reconfigures root logger handlers and strips pytest's ``caplog`` handler [see `PR #2484 <https://www.github.com/FlexMeasures/flexmeasures/pull/2484>`_]
 
 
 

flexmeasures/app.py

@@ -27,6 +27,7 @@ def create(  # noqa C901
     env: str | None = None,
     path_to_config: str | None = None,
     plugins: list[str] | None = None,
+    do_configure_logging: bool = True,
 ) -> Flask:
     """
     Create a Flask app and configure it.
@@ -37,6 +38,8 @@ def create(  # noqa C901
     A path to a config file can be passed in (otherwise a config file will be searched in the home or instance directories).
 
     Also, a list of plugins can be set. Usually this works as a config setting, but this is useful for automated testing.
+
+    Pass ``do_configure_logging=False`` to prevent reconfiguring root logger handlers (e.g. during custom test setup).
     """
 
     from flexmeasures.utils import config_defaults
@@ -53,7 +56,8 @@ def create(  # noqa C901
     from flexmeasures.utils.error_utils import add_basic_error_handlers
     from flexmeasures.utils.secrets_utils import set_secret_key, set_totp_secrets
 
-    configure_logging()  # do this first, see https://flask.palletsprojects.com/en/2.0.x/logging
+    if do_configure_logging and not os.getenv("PYTEST_CURRENT_TEST"):
+        configure_logging()  # do this first, see https://flask.palletsprojects.com/en/2.0.x/logging
     cfg_location = find_flexmeasures_cfg()  # Find flexmeasures.cfg location
     # Create app
     app = Flask("flexmeasures")

flexmeasures/utils/tests/test_config_utils.py

@@ -1,3 +1,4 @@
+import logging
 import pytest
 from flask import Flask
 from werkzeug.sansio.utils import host_is_trusted
@@ -171,3 +172,35 @@ def test_config_warnings_silent_when_trusted_hosts_is_set():
     missing_settings, config_warnings = get_config_warnings(app)
     assert "TRUSTED_HOSTS" not in missing_settings
     assert not any("TRUSTED_HOSTS" in warning for warning in config_warnings)
+
+
+def test_create_app_in_test_does_not_break_caplog(monkeypatch, caplog):
+    """Building a custom app inside a test does not overwrite root logger handlers or break caplog."""
+    import flexmeasures.ui
+    from flexmeasures.app import create as create_app
+
+    monkeypatch.setattr(flexmeasures.ui, "register_at", lambda app: None)
+    custom_app = create_app(env="testing")
+    assert custom_app.testing is True
+
+    with caplog.at_level(logging.WARNING):
+        logging.getLogger().warning("test warning after create_app")
+
+    assert any(
+        record.message == "test warning after create_app" for record in caplog.records
+    )
+
+
+def test_create_app_do_configure_logging_flag(monkeypatch):
+    """create_app respects do_configure_logging."""
+    import flexmeasures.ui
+    from flexmeasures.app import create as create_app
+
+    monkeypatch.setattr(flexmeasures.ui, "register_at", lambda app: None)
+    called = []
+    monkeypatch.setattr(
+        "flexmeasures.utils.config_utils.configure_logging",
+        lambda: called.append(True),
+    )
+    create_app(env="testing", do_configure_logging=False)
+    assert not called