RSpec: how to check file parser

I am new to ruby ​​and rspec, and I am wondering how to test a class that should parse a file. Here is the function I plan to test:

def self.get_description(event_code)
  # search through a file for the event_code and return
  # the associated description field
end

During production, I will hard-code the file path. How can I control the contents of a file from rspec?