Fix string formatting in dispersion cli command

... and add a basic test that would have prevented the regression

Change-Id: I4c5f643ee291dcc1397ca951450459d8b8ad0bbd

swift/cli/ringbuilder.py

@@ -930,13 +930,19 @@ swift-ring-builder <builder_file> dispersion <search_filter> [options]
             for tier_name, dispersion in report['graph']:
                 replica_counts_repr = replica_counts_tmpl % tuple(
                     dispersion['replicas'])
-                print('%-' + str(tier_width) + 's ' + part_count_width +
+                template = ''.join([
-                      ' %6.02f %6d %s') % (tier_name,
+                    '%-', str(tier_width), 's ',
-                                           dispersion['placed_parts'],
+                    part_count_width,
-                                           dispersion['dispersion'],
+                    ' %6.02f %6d %s',
-                                           dispersion['max_replicas'],
+                ])
-                                           replica_counts_repr,
+                args = (
-                                           )
+                    tier_name,
+                    dispersion['placed_parts'],
+                    dispersion['dispersion'],
+                    dispersion['max_replicas'],
+                    replica_counts_repr,
+                )
+                print(template % args)
         exit(status)
 
     def validate():

test/unit/cli/test_ringbuilder.py

@@ -20,6 +20,7 @@ import six
 import tempfile
 import unittest
 import uuid
+import shlex
 
 from swift.cli import ringbuilder
 from swift.common import exceptions
@@ -29,6 +30,9 @@ from swift.common.ring import RingBuilder
 class RunSwiftRingBuilderMixin(object):
 
     def run_srb(self, *argv):
+        if len(argv) == 1 and isinstance(argv[0], basestring):
+            # convert a single string to a list
+            argv = shlex.split(argv[0])
         mock_stdout = six.StringIO()
         mock_stderr = six.StringIO()
 
@@ -40,7 +44,10 @@ class RunSwiftRingBuilderMixin(object):
                     ringbuilder.main(srb_args)
         except SystemExit as err:
             if err.code not in (0, 1):  # (success, warning)
-                raise
+                msg = 'Unexpected exit status %s\n' % err.code
+                msg += 'STDOUT:\n%s\nSTDERR:\n%s\n' % (
+                    mock_stdout.getvalue(), mock_stderr.getvalue())
+                self.fail(msg)
         return (mock_stdout.getvalue(), mock_stderr.getvalue())
 
 
@@ -1741,6 +1748,13 @@ class TestCommands(unittest.TestCase, RunSwiftRingBuilderMixin):
                 err = exc
             self.assertEquals(err.code, 2)
 
+    def test_dispersion_command(self):
+        self.create_sample_ring()
+        self.run_srb('rebalance')
+        out, err = self.run_srb('dispersion -v')
+        self.assertIn('dispersion', out.lower())
+        self.assertFalse(err)
+
 
 class TestRebalanceCommand(unittest.TestCase, RunSwiftRingBuilderMixin):