Testing infinite loop with MiniTest and using mocking - ruby

Question

I have a section in my code which polls a queue for a message and then acts on it depending on the message type:
#queue = Foo::Queue.new
loop do
#queue.poll do |message|
if message[:task] == TAKEACTION
result = takeaction(message)
#queue.send_result(result, message)
end
#queue.pong(message) if message[:task] == PING
end
end
How do I set up a test to supply a single message and verify that the #queue acts on it as I expect?
I have seen very little about testing blocks in minitest, and haven't found anything in ruby regarding breaking out of infinite loops, though I found one idea in python where you set up the second run to throw an exception.
Can any ruby / minitest gurus help?

Answer 1

For minitest using a stub will work. The example below is self contained and can run on its own. You can send an exception as a lambda with a stub to break the infinite loop and continue testing.
# class receiving the messages from class being tested
class Obj
def method_if_true
# do some stuff
return 'anything that is true'
end
def method_if_false
# do some stuff
false
end
end
# class to be tested
class TestingLoop
def initialize(args)
#obj = args.fetch(:object, Obj.new)
#bool = args[:bool]
end
def looping
loop do
if #bool
#obj.method_if_true
# #bool is true
elsif !#bool
#obj.method_if_false
# #bool is false
end
end
end
end
require 'minitest/autorun'
# class that tests
class TestTestingLoop < MiniTest::Test
def setup
#obj = Obj.new
#raises_exception = lambda { raise RuntimeError.new }
# could use the '->' syntax instead of the word lambda
end
def test_sends_correct_method_when_true
#obj.stub :method_if_true, #raises_exception do
testing_loop = TestingLoop.new({object: #obj, bool: true})
assert_raises(RuntimeError) { testing_loop.looping }
end
end
def test_sends_correct_method_when_false
#obj.stub :method_if_false, #raises_exception do
testing_loop = TestingLoop.new({object: #obj, bool: false})
assert_raises(RuntimeError) { testing_loop.looping }
end
end
end