Refactor toward supporting multiple test data resolver types.

test/base/test_data.py

@@ -9,24 +9,38 @@ class TestDataResolver(object):
     def __init__(self, env_var, environ=os.environ):
         file_dirs = environ.get(env_var, None)
         if file_dirs:
-            self.file_dirs = LIST_SEP.split(file_dirs)
+            self.resolvers = map(FileDataResolver, LIST_SEP.split(file_dirs))
         else:
-            self.file_dirs = []
+            self.resolvers = []
 
     def get_filename(self, name):
-        if not self.file_dirs:
+        if not self.resolvers:
             filename = None
         else:
-            filename = os.path.join(self.file_dirs[0], name)
-            # For backward compat. returning first path if none
-            # exist - though I don't know if this function is ever
-            # actually used in a context where one should return
-            # a file even if it doesn't exist (e.g. a prefix or
-            # or something) - I am pretty sure it is not used in
-            # such a fashion in the context of tool tests.
-            if not os.path.exists(filename):
-                for file_dir in self.file_dirs[1:]:
-                    query_filename = os.path.join(file_dir, name)
-                    if os.path.exists(query_filename):
-                        filename = query_filename
+            resolver = self.resolvers[0]
+            filename = resolver.path(name)
+            if not resolver.exists(filename):
+                for resolver in self.resolvers[1:]:
+                    if resolver.exists(name):
+                        filename = resolver.path(name)
+            else:
+                # For backward compat. returning first path if none
+                # exist - though I don't know if this function is ever
+                # actually used in a context where one should return
+                # a file even if it doesn't exist (e.g. a prefix or
+                # or something) - I am pretty sure it is not used in
+                # such a fashion in the context of tool tests.
+                filename = resolver.path(name)
         return os.path.abspath(filename)
+
+
+class FileDataResolver(object):
+
+    def __init__(self, file_dir):
+        self.file_dir = file_dir
+
+    def exists(self, filename):
+        return os.path.exists(self.path(filename))
+
+    def path(self, filename):
+        return os.path.join(self.file_dir, filename)