broke out _defaultMessageSourceStamps()

Broke out code for generating source stamps info for build result
email from buildbot.status.mail.defaultMessage() function into a
new function.

master/buildbot/status/mail.py

@@ -127,6 +127,32 @@ def _defaultMessageProjects(source_stamps, master_status):
     return ', '.join(projects)
 
 
+def _defaultMessageSourceStamps(source_stamps):
+    text = ""
+
+    for ss in source_stamps:
+        source = ""
+
+        if ss.branch:
+            source += "[branch %s] " % ss.branch
+
+        if ss.revision:
+            source += str(ss.revision)
+        else:
+            source += "HEAD"
+
+        if ss.patch:
+            source += " (plus patch)"
+
+        discriminator = ""
+        if ss.codebase:
+            discriminator = " '%s'" % ss.codebase
+
+        text += "Build Source Stamp%s: %s\n" % (discriminator, source)
+
+    return text
+
+
 def defaultMessage(mode, name, build, results, master_status):
     """Generate a buildbot mail message and return a tuple of message text
         and type."""
@@ -145,25 +171,8 @@ def defaultMessage(mode, name, build, results, master_status):
 
     text += "Buildslave for this Build: %s\n\n" % build.getSlavename()
     text += "Build Reason: %s\n" % build.getReason()
-
-    for ss in ss_list:
-        source = ""
-        if ss and ss.branch:
-            source += "[branch %s] " % ss.branch
-        if ss and ss.revision:
-            source += str(ss.revision)
-        else:
-            source += "HEAD"
-        if ss and ss.patch:
-            source += " (plus patch)"
-
-        discriminator = ""
-        if ss.codebase:
-            discriminator = " '%s'" % ss.codebase
-        text += "Build Source Stamp%s: %s\n" % (discriminator, source)
-
+    text += _defaultMessageSourceStamps(ss_list)
     text += "Blamelist: %s\n" % ",".join(build.getResponsibleUsers())
-
     text += "\n"
 
     t = build.getText()

master/buildbot/test/unit/test_status_mail.py

@@ -985,3 +985,42 @@ def testMultiSourceStampsProject(self):
                                                       source_stamp2,
                                                       source_stamp3],
                          Mock()))
+
+
+# Test buildbot.status.mail._defaultMessageSourceStamps() function
+class TestDefaultMessageSourceStamps(unittest.TestCase):
+
+    # utility function to create mocked source stamp object
+    def setUpSourceStamp(self, branch=None, revision=None, patch=None,
+                         codebase=""):
+
+        source_stamp = Mock()
+        source_stamp.branch = branch
+        source_stamp.revision = revision
+        source_stamp.patch = patch
+        source_stamp.codebase = codebase
+
+        return source_stamp
+
+    # test the case where build does not have any source stamps
+    def testNoSourceStamps(self):
+        self.assertEqual(mail._defaultMessageSourceStamps([]), "")
+
+    # test the case with one single minimal source stamp
+    def testOneSourceStamp(self):
+        source_stamp = self.setUpSourceStamp()
+
+        self.assertEqual("Build Source Stamp: HEAD\n",
+                         mail._defaultMessageSourceStamps([source_stamp]))
+
+    # test the case with multiple source stamps, with branches, revisions,
+    # patch and codebase specifications
+    def testMultipleSourceStamps(self):
+        sstamp1 = self.setUpSourceStamp(branch="branch1", revision="rev1")
+        sstamp2 = self.setUpSourceStamp(branch="branch2", revision="rev2",
+                                        patch="dummy", codebase="base1")
+
+        self.assertEqual("Build Source Stamp: [branch branch1] rev1\n"
+                         "Build Source Stamp 'base1': [branch branch2] rev2 "
+                         "(plus patch)\n",
+                         mail._defaultMessageSourceStamps([sstamp1, sstamp2]))