Implements JsonReader (#2)

tests/io/test_file.py

@@ -1,15 +1,11 @@
 import pytest
-from mock import MagicMock
 
 from bonobo import FileWriter, Bag, FileReader
 from bonobo.core.contexts import ComponentExecutionContext
+from bonobo.util.testing import CapturingComponentExecutionContext
 from bonobo.util.tokens import BEGIN, END
 
 
-class CapturingComponentExecutionContext(ComponentExecutionContext):
-    send = MagicMock()
-
-
 @pytest.mark.parametrize(
     'lines,output',
     [