While running the rspec it shows does not implement( allow_any_instance_of )

My rspec line

allow_any_instance_of(School).to receive(:admission).and_return(:body)

I have my admission method in my lib/school.rb module School

def self.admission()

like this, but when i run the rspec it throws error like

Failure/Error: allow_any_instance_of(School).to receive(:admission),and_return(:body)
       School does not implement #admission