[tomoscanbase] add `_get_flats_weights`

# Conflicts:
#	tomoscan/scanbase.py
#	tomoscan/test/test_scanbase.py

tomoscan/test/test_scanbase.py

@@ -77,6 +77,13 @@ class TestFlatFieldCorrection(unittest.TestCase):
     def test_get_flats_weights(self):
         """test the _get_flats_weights function and insure flat weights
         are correct"""
+        projections = {}
+        for i in range(-2, 30):
+            projections[i] = numpy.random.random(100).reshape((10, 10))
+
+        self.scan.projections = projections
+
+    def test_get_flats_weights(self):
         flat_weights = self.scan._get_flats_weights()
         self.assertTrue(isinstance(flat_weights, dict))
         self.assertEqual(len(flat_weights), 32)