So I'm assuming that the Test class and the Info class are in different assemblies, and I'm also assuming that the Info class is in some assembly that you either cannot or don't want to take a dependency on MEF so you cannot actually attribute the class
to be found by MEF.
In such a case there isn't anything that MEF can really do automatically for you, ExportMetadata doesn't do anything magical it is only a simple bag of data. Give what you have right now you could simply take the string and use Activator.CreateInstance to
get an object instance (you might also need the assembly information if the assembly isn't already loaded).
If you know the list of these objects your TestApp could register them as Exports in the container by calling container.AddExportedValue<Info>(new Info()), if you don't have the types specifically but you know the assemblies they live you could write
your own MEF catalog that would find all the types and automatically Export them without the attributes but that is perhaps more work than you might want to do.
If you can explain what your underlying scenario is perhaps we could come up with another way for you to accomplish your goals.