Check that the argument is in fact a directory

If you mistakenly pass a path that isn't a directory, or doens't exist,
you get a traceback that ends with:
 ---
  File "/Users/tony8129/projects/openstack/openstack/requirements/openstack_requirements/cmds/update.py", line 229, in _copy_requires
    dest_path, project.merge_setup_cfg(proj['setup.cfg'], output_extras)))
KeyError: 'setup.cfg'
ERROR: InvocationError: '.../openstack/requirements/.tox/update/bin/update-requirements -H -s ./nova'
---

This is a little confusing.  This patch checks that the arg is a
directory so a more explicit error can be generated.

Change-Id: I9f3f43d5c9b90746bbf2d651ee4cb37afade1528

openstack_requirements/cmds/update.py

@@ -263,6 +263,9 @@ def main(argv=None, stdout=None, _worker=None):
     if len(args) != 1:
         print("Must specify directory to update")
         raise Exception("Must specify one and only one directory to update.")
+    if not os.path.isdir(args[0]):
+        print("%s is not a directory." % (args[0]))
+        raise Exception("%s is not a directory." % (args[0]))
     if stdout is None:
         stdout = sys.stdout
     if _worker is None:

openstack_requirements/tests/test_update.py

@@ -19,6 +19,7 @@ import sys
 import textwrap
 
 import fixtures
+import mock
 import testscenarios
 import testtools
 from testtools import matchers
@@ -216,7 +217,8 @@ Syncing setup.py
 
 class TestMain(testtools.TestCase):
 
-    def test_smoke(self):
+    @mock.patch('os.path.isdir', return_value=True)
+    def test_smoke(self, mock_isdir):
         def check_params(
                 root, source, suffix, softupdate, hacking, stdout, verbose,
                 non_std_reqs):
@@ -232,14 +234,29 @@ class TestMain(testtools.TestCase):
         with fixtures.EnvironmentVariable('NON_STANDARD_REQS', '1'):
             update.main(
                 ['--source', '/dev/null', '/dev/zero'], _worker=check_params)
+        self.expectThat(mock_isdir.called, matchers.Equals(True))
 
-    def test_suffix(self):
+    @mock.patch('os.path.isdir', return_value=True)
+    def test_suffix(self, mock_isdir):
         def check_params(
                 root, source, suffix, softupdate, hacking, stdout, verbose,
                 non_std_reqs):
             self.expectThat(suffix, matchers.Equals('global'))
 
         update.main(['-o', 'global', '/dev/zero'], _worker=check_params)
+        self.expectThat(mock_isdir.called, matchers.Equals(True))
+
+    def test_isdirectory(self):
+        def never_called(
+                root, source, suffix, softupdate, hacking, stdout, verbose,
+                non_std_reqs):
+            self.expectThat(False, matchers.Equals(True),
+                            message=("update.main() should riase an "
+                                     "excpetion before getting here"))
+
+        with testtools.ExpectedException(Exception,
+                                         "/dev/zero is not a directory"):
+            update.main(['/dev/zero'], _worker=never_called)
 
 
 class TestSyncRequirementsFile(testtools.TestCase):

test-requirements.txt

@@ -10,6 +10,7 @@ testscenarios>=0.4 # Apache-2.0/BSD
 testtools>=1.4.0 # MIT
 virtualenv # MIT
 setuptools>=16.0 # PSF/ZPL
+mock>=1.2 # BSD
 
 # this is required for the docs build jobs
 sphinx!=1.2.0,!=1.3b1,<1.3,>=1.1.2 # BSD