Call gc.collect after each test only if the user asks for it

lib/matplotlib/__init__.py

@@ -1577,10 +1577,11 @@ def _init_tests():
 
 
 def _get_extra_test_plugins():
+    from .testing.performgc import PerformGC
     from .testing.noseclasses import KnownFailure
     from nose.plugins import attrib
 
-    return [KnownFailure, attrib.Plugin]
+    return [PerformGC, KnownFailure, attrib.Plugin]
 
 
 def _get_nose_env():

lib/matplotlib/testing/decorators.py

@@ -72,7 +72,6 @@ def failer(*args, **kwargs):
 
 def _do_cleanup(original_units_registry, original_settings):
     plt.close('all')
-    gc.collect()
 
     mpl.rcParams.clear()
     mpl.rcParams.update(original_settings)

lib/matplotlib/testing/performgc.py

@@ -0,0 +1,26 @@
+from __future__ import (absolute_import, division, print_function,
+                        unicode_literals)
+
+import gc
+import os
+from nose.plugins import Plugin
+
+
+class PerformGC(Plugin):
+    """This plugin adds option to call ``gc.collect`` after each test"""
+    enabled = False
+
+    def options(self, parser, env=os.environ):
+        env_opt = 'PERFORM_GC'
+        parser.add_option('--perform-gc', action='store_true',
+                          dest='performGC', default=env.get(env_opt, False),
+                          help='Call gc.collect() after each test')
+
+    def configure(self, options, conf):
+        if not self.can_configure:
+            return
+
+        self.enabled = getattr(options, 'performGC', False)
+
+    def afterTest(self, test):
+        gc.collect()