Added mapnode "serial" input argument comment description

Minor streamlining of serial argument test

Author: dmordom

nipype/pipeline/engine.py

@@ -2009,7 +2009,8 @@ def __init__(self, interface, iterfield, name, serial=False, **kwargs):
             paired (i.e. it does not compute a combinatorial product).
         name : alphanumeric string
             node specific name
-
+        serial : boolean
+            flag to enforce executing the jobs of the mapnode in a serial manner rather than parallel
         See Node docstring for additional keyword arguments.
         """
 

nipype/pipeline/tests/test_engine.py

@@ -630,8 +630,7 @@ def func1(in1):
                               'crashdump_dir': wd}
 
     # test output of num_subnodes method when serial is default (False)
-    num_subnodes_default = n1.num_subnodes()
-    yield assert_equal, num_subnodes_default, len(n1.inputs.in1)
+    yield assert_equal, n1.num_subnodes(), len(n1.inputs.in1)
 
     # test running the workflow on default conditions
     error_raised = False
@@ -644,8 +643,7 @@ def func1(in1):
 
     # test output of num_subnodes method when serial is True
     n1._serial=True
-    num_subnodes_serial = n1.num_subnodes()
-    yield assert_equal, num_subnodes_serial, 1
+    yield assert_equal, n1.num_subnodes(), 1
 
     # test running the workflow on serial conditions
     error_raised = False