Protect ourselves from mock'ed os. #416

14 files changed, 69 insertions, 11 deletions

diff --git a/coverage/annotate.py b/coverage/annotate.py
index 60772656..4060450f 100644
--- a/coverage/annotate.py
+++ b/coverage/annotate.py
@@ -8,8 +8,12 @@ import os
 import re
 
 from coverage.files import flat_rootname
+from coverage.misc import isolate_module
 from coverage.report import Reporter
 
+os = isolate_module(os)
+
+
 class AnnotateReporter(Reporter):
     """Generate annotated source files showing line coverage.
 
diff --git a/coverage/collector.py b/coverage/collector.py
index 42a97f1a..0a43d87c 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -3,14 +3,18 @@
 
 """Raw data collector for coverage.py."""
 
-import os, sys
+import os
+import sys
 
 from coverage import env
 from coverage.backward import iitems
 from coverage.files import abs_file
-from coverage.misc import CoverageException
+from coverage.misc import CoverageException, isolate_module
 from coverage.pytracer import PyTracer
 
+os = isolate_module(os)
+
+
 try:
     # Use the C extension code when we can, for speed.
     from coverage.tracer import CTracer, CFileDisposition   # pylint: disable=no-name-in-module
diff --git a/coverage/config.py b/coverage/config.py
index 458d4903..cd66697d 100644
--- a/coverage/config.py
+++ b/coverage/config.py
@@ -9,7 +9,9 @@ import re
 import sys
 
 from coverage.backward import configparser, iitems, string_class
-from coverage.misc import CoverageException
+from coverage.misc import CoverageException, isolate_module
+
+os = isolate_module(os)
 
 
 class HandyConfigParser(configparser.RawConfigParser):
diff --git a/coverage/control.py b/coverage/control.py
index 1fb0f5bf..16b5f35e 100644
--- a/coverage/control.py
+++ b/coverage/control.py
@@ -23,7 +23,7 @@ from coverage.files import PathAliases, find_python_files, prep_patterns
 from coverage.files import ModuleMatcher, abs_file
 from coverage.html import HtmlReporter
 from coverage.misc import CoverageException, bool_or_none, join_regex
-from coverage.misc import file_be_gone
+from coverage.misc import file_be_gone, isolate_module
 from coverage.monkey import patch_multiprocessing
 from coverage.plugin import FileReporter
 from coverage.plugin_support import Plugins
@@ -32,6 +32,7 @@ from coverage.results import Analysis, Numbers
 from coverage.summary import SummaryReporter
 from coverage.xmlreport import XmlReporter
 
+os = isolate_module(os)
 
 # Pypy has some unusual stuff in the "stdlib".  Consider those locations
 # when deciding where the stdlib is.
diff --git a/coverage/data.py b/coverage/data.py
index fb0b0224..324d7335 100644
--- a/coverage/data.py
+++ b/coverage/data.py
@@ -16,7 +16,9 @@ from coverage import env
 from coverage.backward import iitems, string_class
 from coverage.debug import _TEST_NAME_FILE
 from coverage.files import PathAliases
-from coverage.misc import CoverageException, file_be_gone
+from coverage.misc import CoverageException, file_be_gone, isolate_module
+
+os = isolate_module(os)
 
 
 class CoverageData(object):
diff --git a/coverage/debug.py b/coverage/debug.py
index 8d6892bb..4076b9b2 100644
--- a/coverage/debug.py
+++ b/coverage/debug.py
@@ -7,6 +7,10 @@ import inspect
 import os
 import sys
 
+from coverage.misc import isolate_module
+
+os = isolate_module(os)
+
 
 # When debugging, it can be helpful to force some options, especially when
 # debugging the configuration mechanisms you usually use to control debugging!
diff --git a/coverage/execfile.py b/coverage/execfile.py
index 1845f8d7..844c11bc 100644
--- a/coverage/execfile.py
+++ b/coverage/execfile.py
@@ -10,10 +10,12 @@ import types
 
 from coverage.backward import BUILTINS
 from coverage.backward import PYC_MAGIC_NUMBER, imp, importlib_util_find_spec
-from coverage.misc import ExceptionDuringRun, NoCode, NoSource
+from coverage.misc import ExceptionDuringRun, NoCode, NoSource, isolate_module
 from coverage.phystokens import compile_unicode
 from coverage.python import get_python_source
 
+os = isolate_module(os)
+
 
 class DummyLoader(object):
     """A shim for the pep302 __loader__, emulating pkgutil.ImpLoader.
diff --git a/coverage/files.py b/coverage/files.py
index 2b8727d4..0b5651cb 100644
--- a/coverage/files.py
+++ b/coverage/files.py
@@ -13,12 +13,14 @@ import sys
 
 from coverage import env
 from coverage.backward import unicode_class
-from coverage.misc import CoverageException, join_regex
+from coverage.misc import CoverageException, join_regex, isolate_module
 
 
 RELATIVE_DIR = None
 CANONICAL_FILENAME_CACHE = {}
 
+os = isolate_module(os)
+
 
 def set_relative_directory():
     """Set the directory that `relative_filename` will be relative to."""
diff --git a/coverage/html.py b/coverage/html.py
index de18cefa..8dca6323 100644
--- a/coverage/html.py
+++ b/coverage/html.py
@@ -13,11 +13,13 @@ import coverage
 from coverage import env
 from coverage.backward import iitems
 from coverage.files import flat_rootname
-from coverage.misc import CoverageException, Hasher
+from coverage.misc import CoverageException, Hasher, isolate_module
 from coverage.report import Reporter
 from coverage.results import Numbers
 from coverage.templite import Templite
 
+os = isolate_module(os)
+
 
 # Static files are looked for in a list of places.
 STATIC_PATH = [
diff --git a/coverage/misc.py b/coverage/misc.py
index 44f89772..36e4fe9c 100644
--- a/coverage/misc.py
+++ b/coverage/misc.py
@@ -7,10 +7,34 @@ import errno
 import hashlib
 import inspect
 import os
+import types
 
 from coverage import env
 from coverage.backward import string_class, to_bytes, unicode_class
 
+ISOLATED_MODULES = {}
+
+
+def isolate_module(mod):
+    """Copy a module so that we are isolated from aggressive mocking.
+
+    If a test suite mocks os.path.exists (for example), and then we need to use
+    it during the test, everything will get tangled up if we use their mock.
+    Making a copy of the module when we import it will isolate coverage.py from
+    those complications.
+    """
+    if mod not in ISOLATED_MODULES:
+        new_mod = types.ModuleType(mod.__name__)
+        ISOLATED_MODULES[mod] = new_mod
+        for name in dir(mod):
+            value = getattr(mod, name)
+            if isinstance(value, types.ModuleType):
+                value = isolate_module(value)
+            setattr(new_mod, name, value)
+    return ISOLATED_MODULES[mod]
+
+os = isolate_module(os)
+
 
 # Use PyContracts for assertion testing on parameters and returns, but only if
 # we are running our own test suite.
diff --git a/coverage/plugin_support.py b/coverage/plugin_support.py
index f88342e9..8a4fbec5 100644
--- a/coverage/plugin_support.py
+++ b/coverage/plugin_support.py
@@ -3,12 +3,15 @@
 
 """Support for plugins."""
 
+import os
 import os.path
 import sys
 
-from coverage.misc import CoverageException
+from coverage.misc import CoverageException, isolate_module
 from coverage.plugin import CoveragePlugin, FileTracer, FileReporter
 
+os = isolate_module(os)
+
 
 class Plugins(object):
     """The currently loaded collection of coverage.py plugins."""
diff --git a/coverage/python.py b/coverage/python.py
index 33e6ec01..71b50f0c 100644
--- a/coverage/python.py
+++ b/coverage/python.py
@@ -7,11 +7,13 @@ import os.path
 import zipimport
 
 from coverage import env, files
-from coverage.misc import contract, expensive, NoSource, join_regex
+from coverage.misc import contract, expensive, NoSource, join_regex, isolate_module
 from coverage.parser import PythonParser
 from coverage.phystokens import source_token_lines, source_encoding
 from coverage.plugin import FileReporter
 
+os = isolate_module(os)
+
 
 @contract(returns='bytes')
 def read_python_source(filename):
diff --git a/coverage/report.py b/coverage/report.py
index 78ad7484..df34e43f 100644
--- a/coverage/report.py
+++ b/coverage/report.py
@@ -6,7 +6,9 @@
 import os
 
 from coverage.files import prep_patterns, FnmatchMatcher
-from coverage.misc import CoverageException, NoSource, NotPython
+from coverage.misc import CoverageException, NoSource, NotPython, isolate_module
+
+os = isolate_module(os)
 
 
 class Reporter(object):
diff --git a/coverage/xmlreport.py b/coverage/xmlreport.py
index 998b9599..b8f8a9e4 100644
--- a/coverage/xmlreport.py
+++ b/coverage/xmlreport.py
@@ -9,8 +9,12 @@ import time
 import xml.dom.minidom
 
 from coverage import __url__, __version__, files
+from coverage.misc import isolate_module
 from coverage.report import Reporter
 
+os = isolate_module(os)
+
+
 DTD_URL = (
     'https://raw.githubusercontent.com/cobertura/web/'
     'f0366e5e2cf18f111cbd61fc34ef720a6584ba02'