Added tests (and made them pass) for update_versions_file's output.

src/zc/buildout/buildout.py

@@ -135,7 +135,7 @@ def _format_picked_versions(picked_versions, required_by):
             target = output
         target.append("%s = %s" % (dist_, version))
     output.extend(required_output)
-    return '\n'.join(output)
+    return output
 
 
 _buildout_default_options = _annotate_section({
@@ -1017,16 +1017,18 @@ class Buildout(DictMixin):
         if self.show_picked_versions:
             print_("Versions had to be automatically picked.")
             print_("The following part definition lists the versions picked:")
-            print_(output)
+            print_('\n'.join(output))
 
         if self.update_versions_file:
             # Write to the versions file.
             if os.path.exists(self.update_versions_file):
-                output += ('\n# Added by buildout at %s' %
-                           datetime.datetime.now())
-            output += '\n'
+                output[:1] = [
+                    '',
+                    '# Added by buildout at %s' % datetime.datetime.now()
+                ]
+            output.append('')
             f = open(self.update_versions_file, 'a')
-            f.write(output)
+            f.write(('\n'.join(output)))
             f.close()
             print_("Picked versions have been written to " +
                    self.update_versions_file)

src/zc/buildout/repeatable.txt

@@ -368,8 +368,13 @@ at the end.
 
 The versions file now contains the extra pin:
 
-    >>> 'spam = 2' in open('my_versions.cfg').read()
-    True
+    >>> print_(open('my_versions.cfg').read()) # doctest: +ELLIPSIS
+    <BLANKLINE>
+    ...
+    <BLANKLINE>
+    # Added by buildout at YYYY-MM-DD hh:mm:ss.dddddd
+    spam = 2
+    <BLANKLINE>
 
 And re-running buildout doesn't report any picked versions anymore:
 
@@ -405,8 +410,13 @@ printing them to the console):
 
 The versions file contains the extra pin:
 
-    >>> 'spam = 2' in open('my_versions.cfg').read()
-    True
+    >>> print_(open('my_versions.cfg').read()) # doctest: +ELLIPSIS
+    <BLANKLINE>
+    ...
+    <BLANKLINE>
+    # Added by buildout at YYYY-MM-DD hh:mm:ss.dddddd
+    spam = 2
+    <BLANKLINE>
 
 Because buildout now includes buildout-versions' (and part of the older
 buildout.dumppickedversions') functionality, it warns if these extensions are

src/zc/buildout/tests.py

@@ -3293,7 +3293,9 @@ def test_suite():
                 ),
                (re.compile('executable = %s' % re.escape(sys.executable)),
                 'executable = python'),
-               ])
+               (re.compile(r'\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}\.\d{6}'),
+                'YYYY-MM-DD hh:mm:ss.dddddd'),
+               ]),
             ),
         doctest.DocFileSuite(
             'debugging.txt',