ruby - How to test adding line to error log by causing rescue statement in rspec -

i have foo class.

class foo   def open_url     net::http.start("google.com") |http|       #     end   rescue exception => e     file.open("error.txt","a+"){|f| f.puts e.message }   end end 

and want test rspec.

require_relative 'foo'  describe foo   describe "#open_url"     "should put error log if connection fails"       net::http.stub(:start).and_return(exception)       # check if line error.txt added.     end   end end 

how can check if line inserted error.txt?

you read file writing

describe foo   describe "#open_url"     "should put error log if connection fails"       net::http.stub(:start).and_raise       foo.open_url       file = file.open("error.txt", "r")       # ...     end   end end 

an alternative check file opened: along lines of this

file.should_receive(:open).with("error.txt", "a+", {|f| f.puts e.message })