Convert test_decompression_bomb.py to use unittest module

Tests/test_decompression_bomb.py

@@ -1,37 +1,40 @@
-from tester import *
+from helper import unittest, PillowTestCase, tearDownModule
 
 from PIL import Image
 
 test_file = "Images/lena.ppm"
 
 
-def test_no_warning_small_file():
+class TestDecompressionBomb(PillowTestCase):
+
+    def test_no_warning_small_file(self):
         # Implicit assert: no warning.
         # A warning would cause a failure.
         Image.open(test_file)
 
-
+    def test_no_warning_no_limit(self):
-def test_no_warning_no_limit():
         # Arrange
         # Turn limit off
         Image.MAX_IMAGE_PIXELS = None
-    assert_equal(Image.MAX_IMAGE_PIXELS, None)
+        self.assertEqual(Image.MAX_IMAGE_PIXELS, None)
 
         # Act / Assert
         # Implicit assert: no warning.
         # A warning would cause a failure.
         Image.open(test_file)
 
-
+    def test_warning(self):
-def test_warning():
         # Arrange
         # Set limit to a low, easily testable value
         Image.MAX_IMAGE_PIXELS = 10
-    assert_equal(Image.MAX_IMAGE_PIXELS, 10)
+        self.assertEqual(Image.MAX_IMAGE_PIXELS, 10)
 
         # Act / Assert
-    assert_warning(
+        self.assert_warning(
-        DecompressionBombWarning,
+            Image.DecompressionBombWarning,
             lambda: Image.open(test_file))
 
+if __name__ == '__main__':
+    unittest.main()
+
 # End of file