[autoroll] add tests for autoroll subcommand parsing.

recipe_engine/autoroll.py

Index: recipe_engine/autoroll.py
diff --git a/recipe_engine/autoroll.py b/recipe_engine/autoroll.py
index bb65b11207d85aca2f4fd563d2a89cc0d4d47101..e1143ae1548bafdd4cd18f29042ec124a4f043d7 100644
--- a/recipe_engine/autoroll.py
+++ b/recipe_engine/autoroll.py
@@ -4,6 +4,7 @@
 
 from __future__ import print_function
 
+import argparse
 import copy
 import json
 import logging
@@ -273,7 +274,7 @@ def add_subparser(parser):
     'autoroll', help=helpstr, description=helpstr)
   autoroll_p.add_argument(
     '--output-json',
-    type=os.path.abspath,
+    type=argparse.FileType('w'),

[dnj, 2017/04/27 17:19:03]

I think we should explicitly close this when we're done, now. Also, this file
will be created even if an error happens before it is written. Probably not a
big deal though.

[iannucci, 2017/04/29 18:30:56]

Done.

     help='A json file to output information about the roll to.')
   autoroll_p.add_argument(
     '--verbose-json',
@@ -318,7 +319,6 @@ def main(_package_deps, args):
       run_simulation_test(repo_root, package_spec.recipes_path, ['train'])
 
   if args.output_json:
-    with open(args.output_json, 'w') as f:
-      json.dump(results, f, sort_keys=True, indent=2)
+    json.dump(results, args.output_json, sort_keys=True, indent=2)
 
   return 0