Add test for reproducible --version strings

And add a release note to document the change.

docs/source/release-notes/3.3.0.rst

@@ -19,9 +19,14 @@ You can view the `3.3.0 milestone`_ on GitLab for more details.
 - Added unique error codes for all missing PyFlakes messages (14 new
   codes, see all :ref:`Error / Violation Codes <error_codes>`)
 
-.. links
+- Force ``flake8 --version`` to be repeatable between invocations. (See also
+  `GitLab#297`_)
+
+.. all links
 .. _3.3.0 milestone:
     https://gitlab.com/pycqa/flake8/milestones/16
+
+.. issue links
 .. _GitLab#244:
     https://gitlab.com/pycqa/flake8/issues/244
 .. _GitLab#251:
@@ -30,5 +35,9 @@ You can view the `3.3.0 milestone`_ on GitLab for more details.
     https://gitlab.com/pycqa/flake8/issues/268
 .. _GitLab#290:
     https://gitlab.com/pycqa/flake8/issues/290
+.. _GitLab#297:
+    https://gitlab.com/pycqa/flake8/issues/297
+
+.. merge request links
 .. _GitLab!156:
     https://gitlab.com/pycqa/flake8/merge_requests/156

tests/unit/test_option_manager.py

@@ -137,6 +137,23 @@ def test_generate_versions(optmanager):
             'Testing 100: 0.0.0, Testing 101: 0.0.0, Testing 300: 0.0.0')
 
 
+def test_plugins_are_sorted_in_generate_versions(optmanager):
+    """Verify we sort before joining strings in generate_versions."""
+    optmanager.registered_plugins = [
+        ('pyflakes', '1.5.0'),
+        ('mccabe', '0.7.0'),
+        ('pycodestyle', '2.2.0'),
+        ('flake8-docstrings', '0.6.1'),
+        ('flake8-bugbear', '2016.12.1'),
+    ]
+    assert (optmanager.generate_versions() ==
+            'flake8-bugbear: 2016.12.1, '
+            'flake8-docstrings: 0.6.1, '
+            'mccabe: 0.7.0, '
+            'pycodestyle: 2.2.0, '
+            'pyflakes: 1.5.0')
+
+
 def test_generate_versions_with_format_string(optmanager):
     """Verify a comma-separated string is generated of registered plugins."""
     optmanager.registered_plugins.update([