simplify logging configuration

single default handler and formatter
don't remove handlers
configure level once using setLevel
document logging
reorganize logging tests

tests/test_logging.py

@@ -0,0 +1,91 @@
+import logging
+import sys
+
+import pytest
+
+from flask._compat import StringIO
+from flask.logging import default_handler, has_level_handler, \
+    wsgi_errors_stream
+
+
+@pytest.fixture(autouse=True)
+def reset_logging(monkeypatch):
+    root_handlers = logging.root.handlers[:]
+    root_level = logging.root.level
+
+    logger = logging.getLogger('flask.app')
+    logger.handlers = []
+    logger.setLevel(logging.NOTSET)
+
+    yield
+
+    logging.root.handlers[:] = root_handlers
+    logging.root.setLevel(root_level)
+
+    logger.handlers = []
+    logger.setLevel(logging.NOTSET)
+
+
+def test_logger(app):
+    assert app.logger.name == 'flask.app'
+    assert app.logger.level == logging.NOTSET
+    assert app.logger.handlers == [default_handler]
+
+
+def test_logger_debug(app):
+    app.debug = True
+    assert app.logger.level == logging.DEBUG
+    assert app.logger.handlers == [default_handler]
+
+
+def test_existing_handler(app):
+    logging.root.addHandler(logging.StreamHandler())
+    assert app.logger.level == logging.NOTSET
+    assert not app.logger.handlers
+
+
+def test_wsgi_errors_stream(app, client):
+    @app.route('/')
+    def index():
+        app.logger.error('test')
+        return ''
+
+    stream = StringIO()
+    client.get('/', errors_stream=stream)
+    assert 'ERROR in test_logging: test' in stream.getvalue()
+
+    assert wsgi_errors_stream._get_current_object() is sys.stderr
+
+    with app.test_request_context(errors_stream=stream):
+        assert wsgi_errors_stream._get_current_object() is stream
+
+
+def test_has_level_handler():
+    logger = logging.getLogger('flask.app')
+    assert not has_level_handler(logger)
+
+    handler = logging.StreamHandler()
+    logging.root.addHandler(handler)
+    assert has_level_handler(logger)
+
+    logger.propagate = False
+    assert not has_level_handler(logger)
+    logger.propagate = True
+
+    handler.setLevel(logging.ERROR)
+    assert not has_level_handler(logger)
+
+
+def test_log_view_exception(app, client):
+    @app.route('/')
+    def index():
+        raise Exception('test')
+
+    app.testing = False
+    stream = StringIO()
+    rv = client.get('/', errors_stream=stream)
+    assert rv.status_code == 500
+    assert rv.data
+    err = stream.getvalue()
+    assert 'Exception on / [GET]' in err
+    assert 'Exception: test' in err