webp: add memory leak test

Tests/check_webp_leaks.py

@@ -0,0 +1,37 @@
+from helper import unittest, PillowTestCase
+import sys
+from PIL import Image
+from io import BytesIO
+
+# Limits for testing the leak
+mem_limit = 16 # max increase in MB
+iterations = 5000
+test_file = "Tests/images/hopper.webp"
+
+
+@unittest.skipIf(sys.platform.startswith('win32'), "requires Unix or MacOS")
+class TestWebPLeaks(PillowTestCase):
+
+    def setUp(self):
+        try:
+            from PIL import _webp
+        except ImportError:
+            self.skipTest('WebP support not installed')
+
+    def _get_mem_usage(self):
+        from resource import getpagesize, getrusage, RUSAGE_SELF
+        mem = getrusage(RUSAGE_SELF).ru_maxrss
+        return mem * getpagesize() / 1024 / 1024
+
+    def test_leak_load(self):
+        with open(test_file, 'rb') as f:
+            im_data = f.read()
+        start_mem = self._get_mem_usage()
+        for count in range(iterations):
+            with Image.open(BytesIO(im_data)) as im:
+                im.load()
+            mem = (self._get_mem_usage() - start_mem)
+            self.assertLess(mem, mem_limit, msg='memory usage limit exceeded')
+
+if __name__ == '__main__':
+    unittest.main()