Update file counting test

- It is annoying to only assert on integer equality for count of files
  in a directory (what files?). Add assertions for the desired files.
- Reduce the aforementioned integer. This is because python2 would put
  compiled .pyc files in the same directory as the source .py files. In
  python3, the .pyc files go in a __pycache__ directory.
- Print slightly more helpful failure message if the integers don't
  match

Author: Gerg

tests/common/components.py

@@ -38,9 +38,18 @@ def assert_scripts_are_installed(self, build_dir):
         (fah.expect()
             .path(build_dir, '.bp', 'bin', 'rewrite')
             .root(build_dir, '.bp', 'lib', 'build_pack_utils')
-                .directory_count_equals(20)  # noqa
-                .path('utils.py')
+                .directory_count_equals(11)  # noqa
+                .path('__init__.py')
+                .path('__pycache__')
+                .path('builder.py')
+                .path('cloudfoundry.py')
+                .path('compile_extensions.py')
+                .path('detecter.py') # [sic]
+                .path('downloads.py')
                 .path('process.py')
+                .path('runner.py')
+                .path('utils.py')
+                .path('zips.py')
             .exists())
 
     def assert_config_options(self, build_dir):

tests/common/integration.py

@@ -128,9 +128,10 @@ def does_not_exist(self):
 
     def directory_count_equals(self, cnt):
         root = os.path.join(*self._root)
+        actual = len(os.listdir(root))
         assert \
-            len(os.listdir(root)) == cnt, \
-            "Directory [%s] does not contain [%d] files" % (root, cnt)
+            actual == cnt, \
+            "Directory [%s] contains [%d] files, expected [%d] files" % (root, actual, cnt)
         return self