Update format of `git cl split`

This change updates the output format of `git cl split` when
`description_file` has no footers.

Bug: 1215852
Change-Id: I69764885337ec31134f2b5e2d861930e0bc8cd2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2936161Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: Fangzhen Song <songfangzhen@bytedance.com>

split_cl.py

@@ -60,7 +60,7 @@ def AddUploadedByGitClSplitToDescription(description):
   """
   split_footers = git_footers.split_footers(description)
   lines = split_footers[0]
-  if not lines[-1] or lines[-1].isspace():
+  if lines[-1] and not lines[-1].isspace():
     lines = lines + ['']
   lines = lines + ['This CL was uploaded by git cl split.']
   if split_footers[1]:

tests/split_cl_test.py

+#!/usr/bin/env vpython3
+"""Tests for split_cl."""
+
+import os
+import sys
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+import split_cl
+
+
+class SplitClTest(unittest.TestCase):
+  _description = """Convert use of X to Y in $directory
+
+<add some background about this conversion for the reviewers>
+
+"""
+
+  _footers = 'Bug: 12345'
+
+  def testAddUploadedByGitClSplitToDescription(self):
+    added_line = 'This CL was uploaded by git cl split.'
+
+    # Description without footers
+    self.assertEqual(
+        split_cl.AddUploadedByGitClSplitToDescription(self._description),
+        self._description + added_line)
+    # Description with footers
+    self.assertEqual(
+        split_cl.AddUploadedByGitClSplitToDescription(self._description +
+                                                      self._footers),
+        self._description + added_line + '\n\n' + self._footers)
+
+
+if __name__ == '__main__':
+  unittest.main()