Add test.

test/async/container/.bad.rb

@@ -0,0 +1,28 @@
+#!/usr/bin/env ruby
+# frozen_string_literal: true
+
+# Released under the MIT License.
+# Copyright, 2020-2022, by Samuel Williams.
+
+require_relative '../../../lib/async/container/controller'
+
+class Bad < Async::Container::Controller
+	def setup(container)
+		container.run(name: "bad", count: 1, restart: true) do |instance|
+			# Deliberately missing call to `instance.ready!`:
+			# instance.ready!
+
+			$stdout.puts "Ready..."
+			$stdout.flush
+
+			sleep
+		ensure
+			$stdout.puts "Exiting..."
+			$stdout.flush
+		end
+	end
+end
+
+controller = Bad.new
+
+controller.run

test/async/container/controller.rb

@@ -88,6 +88,38 @@ def controller.setup(container)
 		end
 	end
 
+	with 'bad controller' do
+		let(:controller_path) {File.expand_path(".bad.rb", __dir__)}
+
+		let(:pipe) {IO.pipe}
+		let(:input) {pipe.first}
+		let(:output) {pipe.last}
+
+		let(:pid) {@pid}
+
+		def before
+			@pid = Process.spawn("bundle", "exec", controller_path, out: output)
+			output.close
+
+			super
+		end
+
+		def after
+			Process.kill(:TERM, @pid)
+			Process.wait(@pid)
+
+			super
+		end
+
+		it "fails to start" do
+			expect(input.gets).to be == "Ready...\n"
+
+			Process.kill(:INT, @pid)
+
+			expect(input.gets).to be == "Exiting...\n"
+		end
+	end
+
 	with 'signals' do
 		let(:controller_path) {File.expand_path(".dots.rb", __dir__)}