Test FitsStubImagePlugin for correctness

Tests/test_file_fitsstub.py

@@ -1,17 +1,51 @@
 from helper import unittest, PillowTestCase
 
-from PIL import FitsStubImagePlugin
+from PIL import FitsStubImagePlugin, Image
+
+TEST_FILE = "Tests/images/hopper.fits"
 
 
 class TestFileFitsStub(PillowTestCase):
 
+    def test_open(self):
+        # Act
+        im = Image.open(TEST_FILE)
+
+        # Assert
+        self.assertEqual(im.format, "FITS")
+
+        # Dummy data from the stub
+        self.assertEqual(im.mode, "F")
+        self.assertEqual(im.size, (1, 1))
+
     def test_invalid_file(self):
+        # Arrange
         invalid_file = "Tests/images/flower.jpg"
 
+        # Act / Assert
         self.assertRaises(SyntaxError,
                           lambda:
                           FitsStubImagePlugin.FITSStubImageFile(invalid_file))
 
+    def test_load(self):
+        # Arrange
+        im = Image.open(TEST_FILE)
+
+        # Act / Assert: stub cannot load without an implemented handler
+        self.assertRaises(IOError, lambda: im.load())
+
+    def test_save(self):
+        # Arrange
+        im = Image.open(TEST_FILE)
+        dummy_fp = None
+        dummy_filename = "dummy.filename"
+
+        # Act / Assert: stub cannot save without an implemented handler
+        self.assertRaises(IOError, lambda: im.save(dummy_filename))
+        self.assertRaises(
+            IOError,
+            lambda: FitsStubImagePlugin._save(im, dummy_fp, dummy_filename))
+
 
 if __name__ == '__main__':
     unittest.main()