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.

tests/data/roots/simple_ubuntu/etc/networks/interfaces

@@ -0,0 +1,3 @@
+auto lo
+iface lo inet loopback
+

tests/unittests/helpers.py

@@ -1,8 +1,42 @@
 import os
 
+import mocker
+
 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 first argument
+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 +74,75 @@ 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))

tests/unittests/test_runs/test_simple_run.py

@@ -0,0 +1,89 @@
+from mocker import MockerTestCase
+
+import mocker
+import sys
+import os
+
+# Allow running this test individually
+top_dir = os.path.join(os.path.dirname(__file__), os.pardir, "helpers.py")
+top_dir = os.path.abspath(top_dir)
+if os.path.exists(top_dir):
+    sys.path.insert(0, os.path.dirname(top_dir))
+
+
+import helpers
+
+from cloudinit import util
+from cloudinit import stages
+
+from cloudinit.settings import (PER_INSTANCE)
+
+
+class TestSimpleRunDistro(helpers.FilesystemMockingTestCase):
+    def _patchIn(self, root):
+        self.restore()
+        self.patchOS(root)
+        self.patchUtils(root)
+
+    def _pp_root(self, root, repatch=True):
+        self.restore()
+        for (dirpath, dirnames, filenames) in os.walk(root):
+            print(dirpath)
+            for f in filenames:
+                joined = os.path.join(dirpath, f)
+                if os.path.islink(joined):
+                    print("f %s - (symlink)" % (f))
+                else:
+                    print("f %s" % (f))
+            for d in dirnames:
+                joined = os.path.join(dirpath, d)
+                if os.path.islink(joined):
+                    print("d %s - (symlink)" % (d))
+                else:
+                    print("d %s" % (d))
+        if repatch:
+            self._patchIn(root)
+
+    def test_none_ds(self):
+        new_root = self.makeDir()
+        self.replicateTestRoot('simple_ubuntu', new_root)
+        cfg = {
+            'datasource_list': ['None'],
+            'write_files': [{
+                    'path': '/etc/blah.ini',
+                    'content': 'blah',
+                    'permissions': 0755,
+            }],
+            'cloud_init_modules': ['write-files'],
+        }
+        cloud_cfg = util.yaml_dumps(cfg)
+        util.ensure_dir(os.path.join(new_root, 'etc', 'cloud'))
+        util.write_file(os.path.join(new_root, 'etc',
+                                     'cloud', 'cloud.cfg'), cloud_cfg)
+        self._patchIn(new_root)
+
+        # Now start verifying whats created
+        initer = stages.Init()
+        initer.read_cfg()
+        initer.initialize()
+        self.assertTrue(os.path.exists("/var/lib/cloud"))
+        for d in ['scripts', 'seed', 'instances', 'handlers', 'sem', 'data']:
+            self.assertTrue(os.path.isdir(os.path.join("/var/lib/cloud", d)))
+
+        initer.fetch()
+        iid = initer.instancify()
+        self.assertEquals(iid, 'iid-datasource-none')
+        initer.update()
+        self.assertTrue(os.path.islink("var/lib/cloud/instance"))
+
+        (ran, results) = initer.cloudify().run('consume_userdata',
+                                               initer.consume_userdata,
+                                               args=[PER_INSTANCE],
+                                               freq=PER_INSTANCE)
+
+        mods = stages.Modules(initer)
+        (which_ran, failures) = mods.run_section('cloud_init_modules')
+        self.assertTrue(os.path.exists('/etc/blah.ini'))
+        self.assertIn('write-files', which_ran)
+        contents = util.load_file('/etc/blah.ini')
+        self.assertEquals(contents, 'blah')