Python code refactorings.

This commit refactors the python code in diskimage_builder slightly.  This is
in preparation for a larger review that adds more functionality to the python
code, namely the ability to apply elements to the current system as opposed to
a chroot.  Further, the refactorings can stand on their own for better clarity.
They include:
 - renaming elements.py to element_dependencies.py.  Adds clarity about the
   purpose of this module.
 - updating other code for this rename.
 - move tests into a tests submodule.

Change-Id: I5519cc52398e442b24e33802bae42070d64b0c1d

bin/element-info

@@ -17,7 +17,7 @@
 import os
 import sys
 
-from diskimage_builder.elements import main
+from diskimage_builder.element_dependencies import main
 
 
 sys.exit(main(sys.argv))

diskimage_builder/tests/test_elementdeps.py

@@ -18,7 +18,7 @@ import os
 import fixtures
 import testtools
 
-from diskimage_builder import elements
+from diskimage_builder import element_dependencies
 
 data_dir = os.path.abspath(
     os.path.join(os.path.dirname(__file__), 'test-elements'))
@@ -47,34 +47,35 @@ class TestElementDeps(testtools.TestCase):
         _populate_element(self.element_dir, 'circular2', ['circular1'])
 
     def test_non_transitive_deps(self):
-        result = elements.expand_dependencies(
+        result = element_dependencies.expand_dependencies(
             ['requires-foo'],
             elements_dir=self.element_dir)
         self.assertEqual(set(['requires-foo', 'foo']), result)
 
     def test_missing_deps(self):
-        self.assertRaises(SystemExit, elements.expand_dependencies, ['fake'],
+        self.assertRaises(SystemExit,
+                          element_dependencies.expand_dependencies, ['fake'],
                           self.element_dir)
 
     def test_transitive_deps(self):
-        result = elements.expand_dependencies(
+        result = element_dependencies.expand_dependencies(
             ['requires-requires-foo'], elements_dir=self.element_dir)
         self.assertEqual(set(['requires-requires-foo',
                               'requires-foo',
                               'foo']), result)
 
     def test_no_deps(self):
-        result = elements.expand_dependencies(
+        result = element_dependencies.expand_dependencies(
             ['foo'], elements_dir=self.element_dir)
         self.assertEqual(set(['foo']), result)
 
     def test_self(self):
-        result = elements.expand_dependencies(
+        result = element_dependencies.expand_dependencies(
             ['self'], elements_dir=self.element_dir)
         self.assertEqual(set(['self']), result)
 
     def test_circular(self):
-        result = elements.expand_dependencies(
+        result = element_dependencies.expand_dependencies(
             ['circular1'], elements_dir=self.element_dir)
         self.assertEqual(set(['circular1', 'circular2']), result)
 
@@ -83,8 +84,8 @@ class TestElements(testtools.TestCase):
     def test_depends_on_env(self):
         self.useFixture(
             fixtures.EnvironmentVariable('ELEMENTS_PATH', '/foo/bar'))
-        self.assertEqual('/foo/bar', elements.get_elements_dir())
+        self.assertEqual('/foo/bar', element_dependencies.get_elements_dir())
 
     def test_env_not_set(self):
         self.useFixture(fixtures.EnvironmentVariable('ELEMENTS_PATH', ''))
-        self.assertRaises(Exception, elements.get_elements_dir, ())
+        self.assertRaises(Exception, element_dependencies.get_elements_dir, ())

diskimage_builder/tests/test_elements.py

@@ -30,7 +30,7 @@ def load_tests(loader, tests, pattern):
         # http://bugs.python.org/issue11218
         pattern = "test*.py"
     this_dir = os.path.dirname(__file__)
-    elements_dir = os.path.join(this_dir, "..", "elements")
+    elements_dir = os.path.join(this_dir, "..", "..", "elements")
     # Make a fake elements top level package, as discovery doesn't let us
     # override the python path.
     package = StubPackage()