introduce custom object for cmdline arguments

Allows to define special functions over the arguments.

Also splits CLI tests in two files as they have become too many.

test/python/mocks.py

@@ -0,0 +1,18 @@
+"""
+Custom mocks for testing.
+"""
+
+
+class MockParamCapture:
+    """ Mock that records the parameters with which a function was called
+        as well as the number of calls.
+    """
+    def __init__(self, retval=0):
+        self.called = 0
+        self.return_value = retval
+
+    def __call__(self, *args, **kwargs):
+        self.called += 1
+        self.last_args = args
+        self.last_kwargs = kwargs
+        return self.return_value