How to Test the Private Method of the Model

model

class test
　　def initialize(val1,val2)
　　　　validate(val1,val2)
　　end
　　private 
　　def validate(val1,val2)
　　　　raise xxxx errorless val1.presnet?
　　　　raise yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy
　　end
end

I want to test validate

General Writing

@test=Test.new(val1,val2)
@test.send(:validate,val1,val2)

→Validate runs twice?(when instance is generated and when run in send

Solution
①Stub new and return dummy instances of the Test class?
(I don't know how to use a dummy instance...)

他 Call the private method directly using other methods
(I don't know how to call...)

What do you want to hear

、 and どちらWhich one is better
①How do I return a dummy instance if
②In the case of
how exactly do you call them? I would like to know that

I'm sorry, but I'd appreciate it if you could let me know as a beginner.