tests: add unit-tests for opening

Add unit-tests for verifying the various behaviors associated with
opening a file or hash.

Change-Id: Ie74896b1689cab43d24ebf98ed206864f252184a
Signed-off-by: Patrick Venture <venture@google.com>
diff --git a/firmware_handler.cpp b/firmware_handler.cpp
index f3daae3..0c4014e 100644
--- a/firmware_handler.cpp
+++ b/firmware_handler.cpp
@@ -218,6 +218,8 @@
         /* open() succeeded. */
 
         /* TODO: Actually handle storing this information. */
+
+        return true;
     }
 
     return false;