Update tests.py to allow a single file to be tested, to help work towards #22

tests.py

@@ -39,7 +39,11 @@ def validate(path):
         print("    %sInvalid JSON!%s" % (RED, END))
         return False
 
+if __name__ == "__main__":
     success = True
+    if len(sys.argv) == 2:
+        success = validate(sys.argv[1])
+    else:
         for directory, subdirs, files in os.walk('.'):
             if len(files) > 0:
                 for f in files: