Add helpers for wrapping file operations

Add a new example test that will patch utils and os
functions so that they can be 'retargeted' to a temporary
directory, which allows us the ability to run a full set
of cloud-init stages.

Neat things:

1. All cloud-init code is unchanged (as long as it goes
   through the utils functions for most functionality)
2. Allows for a natural way to setup a temporary directory
   then patch the new directory as the new 'root' and then
   run cloud-init stages and then check the contents of
   what was placed as desired.

Note:
 This is now exposing what I think was just an issue in 
 ./tools/run-pylint.
 ./tools/run-pylint ./tests/unittests/test_filters/test_launch_index.py
and
 ./tools/run-pylint ./tests/unittests/test_simple_run 
 was always failing, but now I'm seeing errors.

need to fix that.  any tests that 'import helper' have issues.

1 files changed, 103 insertions, 0 deletions

diff --git a/tests/unittests/helpers.py b/tests/unittests/helpers.py
index d0f09e70..d5df580b 100644
--- a/tests/unittests/helpers.py
+++ b/tests/unittests/helpers.py
@@ -3,6 +3,37 @@ import os
 from mocker import MockerTestCase
 
 from cloudinit import helpers as ch
+from cloudinit import util
+
+import shutil
+
+# Makes the old path start
+# with new base instead of whatever
+# it previously had
+def rebase_path(old_path, new_base):
+    if old_path.startswith(new_base):
+        # Already handled...
+        return old_path
+    # Retarget the base of that path
+    # to the new base instead of the
+    # old one...
+    path = os.path.join(new_base, old_path.lstrip("/"))
+    path = os.path.abspath(path)
+    return path
+
+
+# Can work on anything that takes a path as arguments
+def retarget_many_wrapper(new_base, am, old_func):
+    def wrapper(*args, **kwds):
+        n_args = list(args)
+        nam = am
+        if am == -1:
+            nam = len(n_args)
+        for i in range(0, nam):
+            path = args[i]
+            n_args[i] = rebase_path(path, new_base)
+        return old_func(*n_args, **kwds)
+    return wrapper
 
 
 class ResourceUsingTestCase(MockerTestCase):
@@ -40,3 +71,75 @@ class ResourceUsingTestCase(MockerTestCase):
             'templates_dir': self.resourceLocation(),
         })
         return cp
+
+
+class FilesystemMockingTestCase(ResourceUsingTestCase):
+    def __init__(self, methodName="runTest"):
+        ResourceUsingTestCase.__init__(self, methodName)
+        self.patched_funcs = []
+
+    def replicateTestRoot(self, example_root, target_root):
+        real_root = self.resourceLocation()
+        real_root = os.path.join(real_root, 'roots', example_root)
+        for (dir_path, _dirnames, filenames) in os.walk(real_root):
+            real_path = dir_path
+            make_path = rebase_path(real_path[len(real_root):], target_root)
+            util.ensure_dir(make_path)
+            for f in filenames:
+                real_path = util.abs_join(real_path, f)
+                make_path = util.abs_join(make_path, f)
+                shutil.copy(real_path, make_path)
+
+    def tearDown(self):
+        self.restore()
+        ResourceUsingTestCase.tearDown(self)
+
+    def restore(self):
+        for (mod, f, func) in self.patched_funcs:
+            setattr(mod, f, func)
+        self.patched_funcs = []
+
+    def patchUtils(self, new_root):
+        patch_funcs = {
+            util: [('write_file', 1),
+                   ('load_file', 1),
+                   ('ensure_dir', 1),
+                   ('chmod', 1),
+                   ('delete_dir_contents', 1),
+                   ('del_file', 1),
+                   ('sym_link', -1)],
+        }
+        for (mod, funcs) in patch_funcs.items():
+            for (f, am) in funcs:
+                func = getattr(mod, f)
+                trap_func = retarget_many_wrapper(new_root, am, func)
+                setattr(mod, f, trap_func)
+                self.patched_funcs.append((mod, f, func))
+
+        # Handle subprocess calls
+        func = getattr(util, 'subp')
+
+        def nsubp(*_args, **_kwargs):
+            return ('', '')
+
+        setattr(util, 'subp', nsubp)
+        self.patched_funcs.append((util, 'subp', func))
+
+        def null_func(*_args, **_kwargs):
+            return None
+
+        for f in ['chownbyid', 'chownbyname']:
+            func = getattr(util, f)
+            setattr(util, f, null_func)
+            self.patched_funcs.append((util, f, func))
+
+    def patchOS(self, new_root):
+        patch_funcs = {
+            os.path: ['isfile', 'exists', 'islink', 'isdir'],
+        }
+        for (mod, funcs) in patch_funcs.items():
+            for f in funcs:
+                func = getattr(mod, f)
+                trap_func = retarget_many_wrapper(new_root, 1, func)
+                setattr(mod, f, trap_func)
+                self.patched_funcs.append((mod, f, func))