How can I test logger-messages with MiniTest? - ruby

Question

I have an application and I want to test if I get correct
messages from my logger.
A short example (you may switch between log4r and logger):
gem 'minitest'
require 'minitest/autorun'
require 'log4r'
#~ require 'logger'
class Testlog < MiniTest::Test
def setup
if defined? Log4r
#log = Log4r::Logger.new('log')
#log.outputters << Log4r::StdoutOutputter.new('stdout', :level => Log4r::INFO)
else
#log = Logger.new(STDOUT)
#log.level = Logger::INFO
end
end
def test_silent
assert_silent{ #log.debug("hello world") }
assert_output(nil,nil){ #log.debug("Hello World") }
end
def test_output
#~ refute_silent{ #log.INFO("Hello") }#-> NoMethodError: undefined method `refute_silent'
assert_output("INFO log: Hello World\n",''){ #log.info("Hello World") }
end
end
But I get:
1) Failure:
Testlog#test_output [minitest_log4r.rb:27]:
In stdout.
Expected: "INFO log: Hello World\n"
Actual: ""
On my output screen I see the message.
I have similar results with Log4r::StderrOutputter and Log4r::Outputter.stdout.
So it seems it is send to the output screen, but it is not catched by minitest in STDOUT or STDERR.
Before I start to write a minitest-log4r-Gem:
Is there a possibility to test logger-output in minitest?
If not:
Any recommendations how to implement a minitest-log4r-Gem?
Examples what I could imagine:
define new outputter for minitest (Log4r::MinitestOutputter)
Mock the logger.
new assertions (add the new outputter as parameter?):
assert_message('INFO log: Hello World'){ #log.info("Hello World") }
assert_messages(:info => 1, :debug => 2){ #log.info("Hello World") } to count messages.
assert_info_messages('Hello World'){ #log.info("Hello World") }
assert_debug_messages('Hello World'){ #log.info("Hello World") }

Answer 1

You can set up a pipe, pass the writer from the pipe to the logger, and then use the reader from the pipe to test your assertions.
http://ruby-doc.org/core-2.1.0/IO.html#method-c-pipe
Something like:
require 'logger'
r, w = IO.pipe
log = Logger.new(w)
log.info "testing info log message"
output = r.gets
puts "Test passed: #{!!(/testing/ =~ output)}"

Answer 2

In meantime I created a minitest-logger-Gem
A code example how to use it:
require 'log4r'
require 'minitest-logger'
class Test_log4r < MiniTest::Test
def setup
#log = Log4r::Logger.new('log')
#log.level = Log4r::INFO
end
def test_output_1
assert_log(" INFO log: Hello World\n"){ #log.info("Hello World") }
end
def test_output_regex
assert_log(/Hello World/){ #log.info("Hello World") }
end
def test_silent
assert_silent_log(){
#log.debug("Hello World")
#~ #log.info("Hello World") #uncomment this to see a failure
}
refute_silent_log(){
#log.warn("Hello World") #comment this to see a failure
}
end
end
During the test a temporary outputter is added to the logger #log. After the test the outputter is removed again.
The gem supports log4r and logger.

Answer 3

#Puhlze answer is good. Just for non-blocking, check before hand if there is input available:
if IO.select([r], [], [], 0.01).nil?

Answer 4

Suppose we have this code here on a file called logger.rb:
require 'logger'
class Framework
attr_reader :logger
def initialize
#logger = Logger.new("/tmp/minitest.log")
end
end
class Custom
def initialize(framework)
#framework = framework
end
def error!
raise StandardError, 'Forced error'
rescue StandardError => e
#framework.logger.error "Error: #{e}"
end
end
And we need to test the logger error messages. We can use a stub method and a StringIO object:
require 'minitest'
require 'minitest/autorun'
require_relative 'logger.rb'
class LoggerTest < MiniTest::Test
def test_logger
framework = Framework.new
custom = Custom.new(framework)
io = StringIO.new
framework.stub :logger, Logger.new(io) do
custom.error!
assert_match(/Forced error/, io.string)
end
end
end
This way we don't need to override the framework logger, just stub it.