I have a method that I need to test:
To invoke this method I need to run server, send a message to it and only then the method will be invoked.
How would I make snapshot (dump) of objectOfBigClass in normal debug mode, and then use it in tests (without need to run server again)?
You could first write a program that sends a message to the server and creates the object. Then save the object to a local file. You can then recreate the object in your test program, by reading the file.
Honestly, why is the object that big? What does it do? Maybe its responsibilities are too much.