Enable showing DeprecationWarning in debug_on and add unit test

satpy/tests/test_utils.py

@@ -17,9 +17,14 @@
 # satpy.  If not, see <http://www.gnu.org/licenses/>.
 """Testing of utils."""
 
+import logging
 import unittest
+import warnings
 from unittest import mock
+
+import pytest
 from numpy import sqrt
+
 from satpy.utils import angle2xyz, lonlat2xyz, xyz2angle, xyz2lonlat, proj_units_to_meters, get_satpos
 
 
@@ -307,3 +312,26 @@ def test_specific_check_satpy(self):
                     checked_fake = True
             self.assertTrue(checked_fake, "Did not find __fake module "
                                           "mentioned in checks")
+
+
+def test_debug_on(caplog):
+    """Test that debug_on is working as expected."""
+    from satpy.utils import debug_on
+
+    def depwarn():
+        logger = logging.getLogger("satpy.silly")
+        logger.debug("But now it's just got SILLY.")
+        warnings.warn("Stop that! It's SILLY.", DeprecationWarning)
+    warnings.filterwarnings("ignore", category=DeprecationWarning)
+    debug_on(False)
+    filts_before = warnings.filters.copy()
+    # test that logging on, but deprecation warnings still off
+    with caplog.at_level(logging.DEBUG):
+        depwarn()
+    assert warnings.filters == filts_before
+    assert "But now it's just got SILLY." in caplog.text
+    debug_on(True)
+    # test that logging on and deprecation warnings on
+    with pytest.warns(DeprecationWarning):
+        depwarn()
+    assert warnings.filters != filts_before

satpy/utils.py

@@ -43,16 +43,39 @@ def ensure_dir(filename):
         os.makedirs(directory)
 
 
-def debug_on():
-    """Turn debugging logging on."""
+def debug_on(dep_warnings=True):
+    """Turn debugging logging on.
+
+    Sets up a StreamHandler to to `sys.stderr` at debug level for all
+    loggers, such that all debug messages (and log messages with higher
+    severity) are logged to the standard error stream.
+
+    By default, since Satpy 0.26, this also enables the global visibility
+    of deprecation warnings.  This can be suppressed by passing a false
+    value.
+
+    Args:
+        dep_warnings (Optional[bool]): Switch on deprecation warnings.
+            Defaults to True.
+
+    Returns:
+        None
+    """
     logging_on(logging.DEBUG)
+    if dep_warnings:
+        dep_warnings_on()
 
 
 def trace_on():
     """Turn trace logging on."""
     logging_on(TRACE_LEVEL)
 
 
+def dep_warnings_on():
+    """Switch on deprecation warnings."""
+    warnings.filterwarnings("default", category=DeprecationWarning)
+
+
 def logging_on(level=logging.WARNING):
     """Turn logging on."""
     global _is_logging_on