Merge pull request #345 from bcipolli/refactor_warning_tests

MRG: Simplify interface for testing of warnings.

This is a fix for #343

New interface: suppress_warnings, clear_and_catch_warnings, and error_warnings.
Deprecate ErrorWarnings, IgnoreWarnings, and catch_warn_reset; nibabel.checkwarns.

Author: matthew-brett

nibabel/checkwarns.py

@@ -12,39 +12,23 @@
 
 import warnings
 
+from .testing import (error_warnings, suppress_warnings)
 
-class ErrorWarnings(warnings.catch_warnings):
-    """ Context manager to check for warnings as errors.  Usually used with
-    ``assert_raises`` in the with block
-
-    Examples
-    --------
-    >>> with ErrorWarnings():
-    ...     try:
-    ...         warnings.warn('Message', UserWarning)
-    ...     except UserWarning:
-    ...         print('I consider myself warned')
-    I consider myself warned
-    """
-    filter = 'error'
-
-    def __init__(self, record=True, module=None):
-        super(ErrorWarnings, self).__init__(record=record, module=module)
-
-    def __enter__(self):
-        mgr = super(ErrorWarnings, self).__enter__()
-        warnings.simplefilter(self.filter)
-        return mgr
-
-
-class IgnoreWarnings(ErrorWarnings):
-    """ Context manager to ignore warnings
-
-    Examples
-    --------
-    >>> with IgnoreWarnings():
-    ...     warnings.warn('Message', UserWarning)
-
-    (and you get no warning)
-    """
-    filter = 'ignore'
+
+warnings.warn('The checkwarns module is deprecated and will be removed in nibabel v3.0', FutureWarning)
+
+
+class ErrorWarnings(error_warnings):
+    def __init__(self, *args, **kwargs):
+        warnings.warn('ErrorWarnings is deprecated and will be removed in '
+                      'nibabel v3.0; use nibabel.testing.error_warnings.',
+                      FutureWarning)
+        super(ErrorWarnings, self).__init__(*args, **kwargs)
+
+
+class IgnoreWarnings(suppress_warnings):
+    def __init__(self, *args, **kwargs):
+        warnings.warn('IgnoreWarnings is deprecated and will be removed in '
+                      'nibabel v3.0; use nibabel.testing.suppress_warnings.',
+                      FutureWarning)
+        super(IgnoreWarnings, self).__init__(*args, **kwargs)

nibabel/testing/__init__.py

@@ -7,22 +7,23 @@
 #
 ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ### ##
 ''' Utilities for testing '''
+from __future__ import division, print_function
+
+import sys
+import warnings
 from os.path import dirname, abspath, join as pjoin
 
 import numpy as np
-from warnings import catch_warnings, simplefilter
-
-# set path to example data
-data_path = abspath(pjoin(dirname(__file__), '..', 'tests', 'data'))
 
 # Allow failed import of nose if not now running tests
 try:
-    import nose.tools as nt
-except ImportError:
-    pass
-else:
     from nose.tools import (assert_equal, assert_not_equal,
                             assert_true, assert_false, assert_raises)
+except ImportError:
+    pass
+
+# set path to example data
+data_path = abspath(pjoin(dirname(__file__), '..', 'tests', 'data'))
 
 
 def assert_dt_equal(a, b):
@@ -56,35 +57,110 @@ def assert_allclose_safely(a, b, match_nans=True):
     assert_true(np.allclose(a, b))
 
 
-class suppress_warnings(catch_warnings):
-    """ Version of ``catch_warnings`` class that suppresses warnings
-    """
-    def __enter__(self):
-        res = super(suppress_warnings, self).__enter__()
-        simplefilter('ignore')
-        return res
+def get_fresh_mod(mod_name=__name__):
+    # Get this module, with warning registry empty
+    my_mod = sys.modules[mod_name]
+    try:
+        my_mod.__warningregistry__.clear()
+    except AttributeError:
+        pass
+    return my_mod
+
+
+class clear_and_catch_warnings(warnings.catch_warnings):
+    """ Context manager that resets warning registry for catching warnings
+
+    Warnings can be slippery, because, whenever a warning is triggered, Python
+    adds a ``__warningregistry__`` member to the *calling* module.  This makes
+    it impossible to retrigger the warning in this module, whatever you put in
+    the warnings filters.  This context manager accepts a sequence of `modules`
+    as a keyword argument to its constructor and:
+
+    * stores and removes any ``__warningregistry__`` entries in given `modules`
+      on entry;
+    * resets ``__warningregistry__`` to its previous state on exit.
+
+    This makes it possible to trigger any warning afresh inside the context
+    manager without disturbing the state of warnings outside.
 
+    For compatibility with Python 3.0, please consider all arguments to be
+    keyword-only.
 
-class catch_warn_reset(catch_warnings):
-    """ Version of ``catch_warnings`` class that resets warning registry
+    Parameters
+    ----------
+    record : bool, optional
+        Specifies whether warnings should be captured by a custom
+        implementation of ``warnings.showwarning()`` and be appended to a list
+        returned by the context manager. Otherwise None is returned by the
+        context manager. The objects appended to the list are arguments whose
+        attributes mirror the arguments to ``showwarning()``.
+
+        NOTE: nibabel difference from numpy: default is True
+
+    modules : sequence, optional
+        Sequence of modules for which to reset warnings registry on entry and
+        restore on exit
+
+    Examples
+    --------
+    >>> import warnings
+    >>> with clear_and_catch_warnings(modules=[np.core.fromnumeric]):
+    ...     warnings.simplefilter('always')
+    ...     # do something that raises a warning in np.core.fromnumeric
     """
-    def __init__(self, *args, **kwargs):
-        self.modules = kwargs.pop('modules', [])
+    class_modules = ()
+
+    def __init__(self, record=True, modules=()):
+        self.modules = set(modules).union(self.class_modules)
         self._warnreg_copies = {}
-        super(catch_warn_reset, self).__init__(*args, **kwargs)
+        super(clear_and_catch_warnings, self).__init__(record=record)
 
     def __enter__(self):
         for mod in self.modules:
             if hasattr(mod, '__warningregistry__'):
                 mod_reg = mod.__warningregistry__
                 self._warnreg_copies[mod] = mod_reg.copy()
                 mod_reg.clear()
-        return super(catch_warn_reset, self).__enter__()
+        return super(clear_and_catch_warnings, self).__enter__()
 
     def __exit__(self, *exc_info):
-        super(catch_warn_reset, self).__exit__(*exc_info)
+        super(clear_and_catch_warnings, self).__exit__(*exc_info)
         for mod in self.modules:
             if hasattr(mod, '__warningregistry__'):
                 mod.__warningregistry__.clear()
             if mod in self._warnreg_copies:
                 mod.__warningregistry__.update(self._warnreg_copies[mod])
+
+
+class error_warnings(clear_and_catch_warnings):
+    """ Context manager to check for warnings as errors.  Usually used with
+    ``assert_raises`` in the with block
+
+    Examples
+    --------
+    >>> with error_warnings():
+    ...     try:
+    ...         warnings.warn('Message', UserWarning)
+    ...     except UserWarning:
+    ...         print('I consider myself warned')
+    I consider myself warned
+    """
+    filter = 'error'
+
+    def __enter__(self):
+        mgr = super(error_warnings, self).__enter__()
+        warnings.simplefilter(self.filter)
+        return mgr
+
+
+class suppress_warnings(error_warnings):
+    """ Version of ``catch_warnings`` class that suppresses warnings
+    """
+    filter = 'ignore'
+
+
+class catch_warn_reset(clear_and_catch_warnings):
+    def __init__(self, *args, **kwargs):
+        warnings.warn('catch_warn_reset is deprecated and will be removed in '
+                      'nibabel v3.0; use nibabel.testing.clear_and_catch_warnings.',
+                      FutureWarning)

nibabel/tests/test_arraywriters.py

@@ -11,24 +11,19 @@
 import numpy as np
 
 from ..externals.six import BytesIO
-
 from ..arraywriters import (SlopeInterArrayWriter, SlopeArrayWriter,
                             WriterError, ScalingError, ArrayWriter,
                             make_array_writer, get_slope_inter)
-
 from ..casting import int_abs, type_info, shared_range, on_powerpc
-
 from ..volumeutils import array_from_file, apply_read_scaling, _dt_min_max
 
 from numpy.testing import (assert_array_almost_equal,
                            assert_array_equal)
-
 from nose.tools import (assert_true, assert_false,
                         assert_equal, assert_not_equal,
                         assert_raises)
-
-from ..testing import assert_allclose_safely, suppress_warnings
-from ..checkwarns import ErrorWarnings
+from ..testing import (assert_allclose_safely, suppress_warnings,
+                       error_warnings)
 
 
 FLOAT_TYPES = np.sctypes['float']
@@ -524,7 +519,7 @@ def test_nan2zero():
         data_back = round_trip(aw)
         assert_array_equal(np.isnan(data_back), [True, False])
         # Deprecation warning for nan2zero as argument to `to_fileobj`
-        with ErrorWarnings():
+        with error_warnings():
             assert_raises(DeprecationWarning,
                           aw.to_fileobj, BytesIO(), 'F', True)
             assert_raises(DeprecationWarning,
@@ -545,7 +540,7 @@ def test_nan2zero():
         astype_res = np.array(np.nan).astype(np.int32)
         assert_array_equal(data_back, [astype_res, 99])
         # Deprecation warning for nan2zero as argument to `to_fileobj`
-        with ErrorWarnings():
+        with error_warnings():
             assert_raises(DeprecationWarning,
                           aw.to_fileobj, BytesIO(), 'F', False)
             assert_raises(DeprecationWarning,

nibabel/tests/test_checkwarns.py

@@ -1,42 +1,21 @@
 """ Tests for warnings context managers
 """
-
 from __future__ import division, print_function, absolute_import
 
-from warnings import warn, simplefilter, filters
-
-from ..checkwarns import ErrorWarnings, IgnoreWarnings
-
 from nose.tools import assert_true, assert_equal, assert_raises
+from ..testing import clear_and_catch_warnings, suppress_warnings
 
 
-def test_warn_error():
-    # Check warning error context manager
-    n_warns = len(filters)
-    with ErrorWarnings():
-        assert_raises(UserWarning, warn, 'A test')
-    with ErrorWarnings() as w: # w not used for anything
-        assert_raises(UserWarning, warn, 'A test')
-    assert_equal(n_warns, len(filters))
-    # Check other errors are propagated
-    def f():
-        with ErrorWarnings():
-            raise ValueError('An error')
-    assert_raises(ValueError, f)
+def test_ignore_and_error_warnings():
+    with suppress_warnings():
+        from .. import checkwarns
 
+    with clear_and_catch_warnings() as w:
+        checkwarns.IgnoreWarnings()
+        assert_equal(len(w), 1)
+        assert_equal(w[0].category, FutureWarning)
 
-def test_warn_ignore():
-    # Check warning ignore context manager
-    n_warns = len(filters)
-    with IgnoreWarnings():
-        warn('Here is a warning, you will not see it')
-        warn('Nor this one', DeprecationWarning)
-    with IgnoreWarnings() as w: # w not used
-        warn('Here is a warning, you will not see it')
-        warn('Nor this one', DeprecationWarning)
-    assert_equal(n_warns, len(filters))
-    # Check other errors are propagated
-    def f():
-        with IgnoreWarnings():
-            raise ValueError('An error')
-    assert_raises(ValueError, f)
+    with clear_and_catch_warnings() as w:
+        checkwarns.ErrorWarnings()
+        assert_equal(len(w), 1)
+        assert_equal(w[0].category, FutureWarning)

nibabel/tests/test_openers.py

@@ -12,14 +12,15 @@
 from bz2 import BZ2File
 from io import BytesIO, UnsupportedOperation
 
-from ..checkwarns import ErrorWarnings
 from ..py3k import asstr, asbytes
 from ..openers import Opener, ImageOpener
 from ..tmpdirs import InTemporaryDirectory
 from ..volumeutils import BinOpener
 
 from nose.tools import (assert_true, assert_false, assert_equal,
                         assert_not_equal, assert_raises)
+from ..testing import error_warnings
+
 
 class Lunk(object):
     # bare file-like for testing
@@ -84,7 +85,7 @@ def test_Opener_various():
                     assert_not_equal(fobj.fileno(), 0)
 
 def test_BinOpener():
-    with ErrorWarnings():
+    with error_warnings():
         assert_raises(DeprecationWarning,
                       BinOpener, 'test.txt', 'r')
 

nibabel/tests/test_parrec.py

@@ -23,7 +23,7 @@
 from nose.tools import (assert_true, assert_false, assert_raises,
                         assert_equal)
 
-from ..testing import catch_warn_reset, suppress_warnings
+from ..testing import clear_and_catch_warnings, suppress_warnings
 
 from .test_arrayproxy import check_mmap
 from . import test_spatialimages as tsi
@@ -237,7 +237,7 @@ def test_affine_regression():
 
 def test_get_voxel_size_deprecated():
     hdr = PARRECHeader(HDR_INFO, HDR_DEFS)
-    with catch_warn_reset(modules=[parrec], record=True) as wlist:
+    with clear_and_catch_warnings(modules=[parrec], record=True) as wlist:
         simplefilter('always')
         hdr.get_voxel_size()
     assert_equal(wlist[0].category, DeprecationWarning)
@@ -255,7 +255,7 @@ def test_get_sorted_slice_indices():
                         17, 16, 15, 14, 13, 12, 11, 10, 9,
                         26, 25, 24, 23, 22, 21, 20, 19, 18])
     # Omit last slice, only two volumes
-    with catch_warn_reset(modules=[parrec], record=True):
+    with clear_and_catch_warnings(modules=[parrec], record=True):
         hdr = PARRECHeader(HDR_INFO, HDR_DEFS[:-1], permit_truncated=True)
     assert_array_equal(hdr.get_sorted_slice_indices(), range(n_slices - 9))
 
@@ -300,7 +300,7 @@ def test_truncated_load():
     with open(TRUNC_PAR, 'rt') as fobj:
         gen_info, slice_info = parse_PAR_header(fobj)
     assert_raises(PARRECError, PARRECHeader, gen_info, slice_info)
-    with catch_warn_reset(record=True) as wlist:
+    with clear_and_catch_warnings(record=True) as wlist:
         hdr = PARRECHeader(gen_info, slice_info, True)
         assert_equal(len(wlist), 1)
 
@@ -373,7 +373,7 @@ def test_truncations():
     # Drop one line, raises error
     assert_raises(PARRECError, PARRECHeader, gen_info, slice_info[:-1])
     # When we are permissive, we raise a warning, and drop a volume
-    with catch_warn_reset(modules=[parrec], record=True) as wlist:
+    with clear_and_catch_warnings(modules=[parrec], record=True) as wlist:
         hdr = PARRECHeader(gen_info, slice_info[:-1], permit_truncated=True)
         assert_equal(len(wlist), 1)
     assert_equal(hdr.get_data_shape(), (80, 80, 10))