test_mode: at_exit hook hangs forever because flush spins on non-empty NoopWorker queue

[lorismaz]

Bug description

When test_mode = true is set (as recommended for test/development environments), the posthog-rails railtie registers an at_exit hook:

# posthog-rails/lib/posthog/rails/railtie.rb:111
at_exit { PostHog.client&.shutdown if PostHog.initialized? }

shutdown calls flush (in posthog-ruby/lib/posthog/client.rb):

def flush
  while !@queue.empty? || @worker.is_requesting?
    ensure_worker_running
    sleep(0.1)
  end
end

In test mode, the worker is a NoopWorker which never processes events from the queue. Any PostHog.capture call adds to the queue but nothing drains it. So flush spins in an infinite sleep(0.1) loop and the process never exits.

Impact

This affects any Rails app using posthog-rails with test_mode = true that calls PostHog.capture during tests. The test process hangs indefinitely after all tests pass, making CI pipelines stall.

Reproduction

# config/initializers/posthog.rb
PostHog.init do |config|
  config.api_key = "phc_your_key"
  config.test_mode = Rails.env.test?
end

# Any test that triggers PostHog.capture
PostHog.capture(distinct_id: "user_1", event: "test_event")
# Process will hang on exit

Suggested fix

flush should respect test_mode and skip the drain loop, or shutdown should clear the queue when using NoopWorker:

def flush
  return @queue.clear if @worker.is_a?(NoopWorker)

  while !@queue.empty? || @worker.is_requesting?
    ensure_worker_running
    sleep(0.1)
  end
end

Workaround

# test/test_helper.rb
PostHog.client.define_singleton_method(:flush) { @queue.clear }
PostHog.client.define_singleton_method(:shutdown) { @queue.clear }

Environment

• posthog-ruby 3.5.5
• posthog-rails 3.5.4
• Ruby 3.4.7
• Rails 8.1.1

[lorismaz]

Related to #10 — same root cause in Client#flush. The while !@queue.empty? loop doesn't account for worker types that don't consume the queue (NoopWorker in test mode, or the background thread not running in Sidekiq/Resque).

A fix for flush that checks the worker type would address both issues.