Fix testbook decorator return value (#145)

Author: rohitsanj

testbook/testbook.py

@@ -60,7 +60,7 @@ def __call__(self, func):
         def wrapper(*args, **kwargs):  # pragma: no cover
             with self.client.setup_kernel():
                 self._prepare()
-                func(self.client, *args, **kwargs)
+                return func(self.client, *args, **kwargs)
 
         wrapper.patchings = [self]
         return wrapper

testbook/tests/test_testbook.py

@@ -68,3 +68,11 @@ def test_testbook_with_notebook_node():
 
     with testbook(nb) as tb:
         assert tb.code_cells_executed == 0
+
+
+def test_function_with_testbook_decorator_returns_value():
+    @testbook('testbook/tests/resources/inject.ipynb')
+    def test_function(tb):
+        return "This should be returned"
+
+    assert test_function() == "This should be returned"