Looking to the add() signatures, not sure if the existing ones will adapt to the case:

```
add(CompoundValueNode* node);
add(const Type _type, const std::string& _name, const std::string& _containerPath, const std::string& _value = "");```

Because in this case, we don't use container path (moreover, path is one of the variables candidate to remove in CompoundValue class).

Another posibility would be to define a addLeaf() method (with "name" and "value" as arguments), to make explicit that the child added is a Leaf node.

However, I think that we can defer this constructor adjustment to the PR in which the queryContext functionality at mongoBackend gets implemented, as is better the "real requirement" come from that part, not for the unit test. For not forgetting that, I will mark this with FIXME.