Add separate stream handler for error logging (#1292)

* Add separate stream handler for error logging

* test stdout and stderr

* review refactor, newline after test

* mock instead of unittest.mock

* use filter instead of lambda

* add result checks

* remove Logger pseudo-integration test, add direct test

* tests, refactor, StringIO intercepts stdout and stderr messages

* Check exact error message

Co-Authored-By: pared <[email protected]>

* Check exact non-error message

Co-Authored-By: pared <[email protected]>

dvc/logger.py

@@ -54,11 +54,22 @@ class Logger(object):
 
     @staticmethod
     def init():
-        sh = logging.StreamHandler(sys.stdout)
-        sh.setFormatter(logging.Formatter(Logger.FMT))
-        sh.setLevel(logging.DEBUG)
 
-        Logger.logger().addHandler(sh)
+        class LogLevelFilter(logging.Filter):
+            def filter(self, record):
+                return record.levelno <= logging.WARNING
+
+        sh_out = logging.StreamHandler(sys.stdout)
+        sh_out.setFormatter(logging.Formatter(Logger.FMT))
+        sh_out.setLevel(logging.DEBUG)
+        sh_out.addFilter(LogLevelFilter())
+
+        sh_err = logging.StreamHandler(sys.stderr)
+        sh_err.setFormatter(logging.Formatter(Logger.FMT))
+        sh_err.setLevel(logging.ERROR)
+
+        Logger.logger().addHandler(sh_out)
+        Logger.logger().addHandler(sh_err)
         Logger.set_level()
 
     @staticmethod

tests/test_logger.py

@@ -1,13 +1,26 @@
+from mock import patch
+
+try:
+    from StringIO import StringIO
+except ImportError:
+    from io import StringIO
+
 import colorama
 import logging
 
 from dvc.command.base import CmdBase
 from dvc.config import Config
 from dvc.logger import Logger
+from dvc.main import main
 
 from tests.basic_env import TestDvc
 
 
+class StringContaining(str):
+    def __eq__(self, other):
+        return self in other
+
+
 class TestLogger(TestDvc):
     def test_config(self):
         Logger('debug')
@@ -34,6 +47,28 @@ class TestLogger(TestDvc):
             # This is not a tty, so it should not colorize anything
             self.assertEqual(msg, name)
 
+    @patch('sys.stderr', new_callable=StringIO)
+    @patch('sys.stdout', new_callable=StringIO)
+    def test_stderr(self, mock_stdout, mock_stderr):
+        error_message = 'error msg'
+        Logger.init()
+        Logger.error(error_message)
+        self.assertEqual('', mock_stdout.getvalue())
+        self.assertEqual('Error: {}\n\nHaving any troubles? '
+                                   'Hit us up at dvc.org/support, we '
+                                   'are always happy to help!\n'.format(error_message),
+                                   mock_stderr.getvalue())
+
+    @patch('sys.stderr', new_callable=StringIO)
+    @patch('sys.stdout', new_callable=StringIO)
+    def test_stdout(self, mock_stdout, mock_stderr):
+        non_error_message = 'non-error message'
+        Logger.init()
+        Logger.info(non_error_message)
+        self.assertEqual('', mock_stderr.getvalue())
+        self.assertEqual('{}\n'.format(non_error_message),
+                                   mock_stdout.getvalue())
+
 
 class TestLoggerCLI(TestDvc):
     def test(self):