Add unit tests for ds-identify, fix Ec2 bug found.

This adds several unit tests for ds-identify, and fixes a bug
in Ec2 detection that I found while writing these tests.

The method of testing is to use the ds-identify code as a shell
library. The TestDsIdentify:call basically does:

  * populate a (temp) directory with files that represent what
    ds-identify would see in /sys or other locations it reads.
  * create a file '_shwrap' that replaces the 3 programs that are executed
    in ds-identify code path. It supports setting their stdout, stderr,
    and exit code.
  * set the default policies explicitly (DI_DEFAULT_POLICY) so we can
    support testing different builtins. This is necessary because the
    Ubuntu branches patch the builtin value. If we did not explicilty set
    it, then testing there would fail.
  * execute sh to source the script and call its main.

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/unittests/helpers.py b/tests/unittests/helpers.py
index 90e2431f..a711404c 100644
--- a/tests/unittests/helpers.py
+++ b/tests/unittests/helpers.py
@@ -3,6 +3,7 @@
 from __future__ import print_function
 
 import functools
+import json
 import os
 import shutil
 import sys
@@ -280,6 +281,12 @@ def dir2dict(startdir, prefix=None):
     return flist
 
 
+def json_dumps(data):
+    # print data in nicely formatted json.
+    return json.dumps(data, indent=1, sort_keys=True,
+                      separators=(',', ': '))
+
+
 def wrap_and_call(prefix, mocks, func, *args, **kwargs):
     """
     call func(args, **kwargs) with mocks applied, then unapplies mocks