RSpec loop testing with console input and output - ruby

Question

I have an input method, that intended to read circle radius from console. If input is invalid, method outputs error message and loops to read input again.
So I need to make an rspec test that iterates by array of invalid inputs and expect that
input method will output error to console message each time.
Here is my input class:
# frozen_string_literal: true
require_relative '../data/messages'
# Input class is responsible for reading and writing to and from console and
# querying user
class Input
def read
loop do
print "#{RADIUS_QUERY_MSG}\n> "
radius = gets.strip
return radius.to_f if valid?(radius)
puts INVALID_MSG
end
end
private
def valid?(radius)
/\A[+]?\d+(\.\d+)?\z/.match(radius)
end
end
I've tried this in my rspec test, but it seems to get into some infinite loop:
# frozen_string_literal: true
require 'input'
require_relative '../data/messages'
require_relative '../data/rspec'
RSpec.describe Input do
let(:input) { described_class.new }
describe '#read' do
INVALID_INPUTS.each do |invalid_input|
context "with invalid input \"#{invalid_input}\"" do
it 'tells user that input is invalid' do
allow(input).to receive(:gets).and_return(invalid_input)
expect(input.read).to output("#{INVALID_MSG}\n").to_stdout
end
end
end
end
end
How can I do this properly? Would appreciate any help.
P.S.
Found this article, but it was no use for me. Maybe it will help. https://haughtcodeworks.com/blog/software-development/easy-loop-testing/
P.P.S.
INVALID_MSG and RADIUS_QUERY_MSG are strings and INVALID_INPUTS is an array of strings.

Answer 1

Refactor to Inject Your Test Inputs into the "Real" Method
This is a common problem for code that isn't written test-first. There are a couple of ways to solve it, but the simplest option without mocking, stubbing, or otherwise invalidating your "real" code is simply to refactor the method itself. For example:
def read test_input: nil
loop do
print "#{RADIUS_QUERY_MSG}\n> "
radius = (test_input || gets).strip
return radius.to_f if valid?(radius)
puts INVALID_MSG
end
end
Now you can simply inject whatever values you want into the optional test_input keyword argument from your RSpec tests to ensure that the input is stripped properly and exhibits whatever other behavior you're testing for.
This avoids all sorts of problems you might experience by trying to write around a difficult-to-test method. Either you provide test input directly to the method, in which case the method uses that, or you don't, in which case it calls #gets just as it normally would.
Remember, the goal isn't to test core methods like #gets. Instead, you should be testing the behavior of your method or object given a particular input or state. If you make your methods testable by allowing dependency injection in your code, or refactoring your class to allow modifying instance variables in your test setup and using those rather than method arguments passed to your methods, you ensure that you are testing your real class or method rather than hacking your way around it.
There are certainly other, more complex ways to do what I did above, but they don't seem warranted for this specific example. The KISS principle definitely applies!