Base docker healthcheck on STDOUT logs - ruby

Question

I've got a script that outputs logs to STDOUT. I want to monitor this, and if x seconds passes without log output, the healthcheck should fail and the container should restart.
I've got something that I feel should work (using strace), but it's not. I'll post the files below. Does anyone have any idea how to solve this?
Dockerfile:
FROM ruby:2.5.1
RUN apt-get update
RUN dpkg --configure -a
ENV TZ=Europe/London
RUN ln -snf /usr/share/zoneinfo/$TZ /etc/localtime && echo $TZ > /etc/timezone
RUN DEBIAN_FRONTEND=noninteractive apt-get install -y keyboard-configuration
RUN apt-get install -y --fix-missing curl gnupg build-essential mosh iceweasel git libappindicator1 postgresql libpq-dev xvfb xorg dbus-x11
RUN apt-get install -y --fix-missing libxss1 nodejs xfonts-100dpi xfonts-75dpi sqlite libindicator7 unzip wget curl bzip2 libssl-dev libreadline-dev zlib1g-dev strace
RUN ln -sf /usr/bin/nodejs /usr/local/bin/node
RUN gem install bundler activerecord activesupport watir watir-scroll nokogiri pg pry forgery rspec headless rake vcr webmock rails logger
WORKDIR /home/
COPY . .
HEALTHCHECK --interval=25s --timeout=5s --retries=5 CMD strace -p $(pgrep -n ruby) 2>&1 | grep -m 1 write\(
CMD ["ruby", "./test.rb"]
test.rb:
require 'logger'
$logger = Logger.new(STDOUT)
$logger.level = Logger::DEBUG
loop do
sleep 5
$logger.warn 'hi'
end
Logs are outputting as expected when running docker container log, but the health status is always starting, and shortly after starting it will consider it failed and restart. I intend to use Docker Swarm once this is working.