Add initial postprocess unit test thingy.

recipe_engine/third_party/astunparse/__main__.py

Index: recipe_engine/third_party/astunparse/__main__.py
diff --git a/recipe_engine/third_party/astunparse/__main__.py b/recipe_engine/third_party/astunparse/__main__.py
new file mode 100644
index 0000000000000000000000000000000000000000..1efec7b467dc964c66aed83ffffcd4ab0f54e1f2
--- /dev/null
+++ b/recipe_engine/third_party/astunparse/__main__.py
@@ -0,0 +1,48 @@
+from __future__ import print_function
+import sys
+import os
+import argparse
+from .unparser import roundtrip
+from . import dump
+
+
+def roundtrip_recursive(target, dump_tree=False):
+    if os.path.isfile(target):
+        print(target)
+        print("=" * len(target))
+        if dump_tree:
+            dump(target)
+        else:
+            roundtrip(target)
+        print()
+    elif os.path.isdir(target):
+        for item in os.listdir(target):
+            if item.endswith(".py"):
+                roundtrip_recursive(os.path.join(target, item), dump_tree)
+    else:
+        print(
+            "WARNING: skipping '%s', not a file or directory" % target,
+            file=sys.stderr
+        )
+
+
+def main(args):
+    parser = argparse.ArgumentParser(prog="astunparse")
+    parser.add_argument(
+        'target',
+        nargs='+',
+        help="Files or directories to show roundtripped source for"
+    )
+    parser.add_argument(
+        '--dump',
+        type='bool',
+        help="Show a pretty-printed AST instead of the source"
+    )
+
+    arguments = parser.parse_args(args)
+    for target in arguments.target:
+        roundtrip_recursive(target, dump_tree=arguments.dump)
+
+
+if __name__ == "__main__":
+    main(sys.argv[1:])