git cl issue: add --json switch for machine-readable output

tests/git_cl_test.py

Index: tests/git_cl_test.py
diff --git a/tests/git_cl_test.py b/tests/git_cl_test.py
index d4603ed3da7108aed8b306ed8bdff1c42e01790e..72020ffe5dcf80a63561cbdd7570fcf667dc3404 100755
--- a/tests/git_cl_test.py
+++ b/tests/git_cl_test.py
@@ -251,6 +251,8 @@ class TestGitCl(TestCase):
     self.mock(git_cl, 'BranchExists', lambda _: True)
     self.mock(git_cl, 'FindCodereviewSettingsFile', lambda: '')
     self.mock(git_cl, 'ask_for_data', self._mocked_call)
+    self.mock(git_cl, 'write_json', lambda path, contents:
+        self._mocked_call('write_json', path, contents))
     self.mock(git_cl.presubmit_support, 'DoPresubmitChecks', PresubmitMock)
     self.mock(git_cl.rietveld, 'Rietveld', RietveldMock)
     self.mock(git_cl.rietveld, 'CachingRietveld', RietveldMock)
@@ -1759,6 +1761,22 @@ class TestGitCl(TestCase):
     ]
     self.assertEqual(0, git_cl.main(['issue', '0']))
 
+  def test_cmd_issue_json(self):
+    out = StringIO.StringIO()
+    self.mock(git_cl.sys, 'stdout', out)
+    self.calls = [
+        ((['git', 'symbolic-ref', 'HEAD'],), 'feature'),
+        ((['git', 'config', '--int', 'branch.feature.rietveldissue'],), '123'),
+        ((['git', 'config', 'rietveld.autoupdate'],), ''),
+        ((['git', 'config', 'rietveld.server'],),
+         'https://codereview.chromium.org'),
+        ((['git', 'config', 'branch.feature.rietveldserver'],), ''),
+        (('write_json', 'output.json',
+          {'issue': 123, 'issue_url': 'https://codereview.chromium.org/123'}),
+         ''),
+    ]
+    self.assertEqual(0, git_cl.main(['issue', '--json', 'output.json']))
+
   def test_git_cl_try_default(self):
     self.mock(git_cl.Changelist, 'GetChange',
               lambda _, *a: (