diff --git a/ruby/shell/job_control.rb b/ruby/shell/job_control.rb
index f116895..156d79f 100644
--- a/ruby/shell/job_control.rb
+++ b/ruby/shell/job_control.rb
@@ -10,9 +10,10 @@ module Shell
 
     attr_reader :logger
 
-    def initialize(logger: nil)
+    def initialize(logger: nil, refresh_line: nil)
       @jobs_by_pid = {}
       @logger = logger || Logger.instance
+      @refresh_line = refresh_line || -> { Readline.refresh_line }
     end
 
     def exec_command(cmd, args, background: false)
@@ -67,7 +68,11 @@ module Shell
     def trap_sigchld
       # handler for SIGCHLD when a child's state changes
       Signal.trap("CHLD") do |_signo|
-        pid = Process.waitpid(-1, Process::WNOHANG)
+        pid = begin
+          Process.waitpid(-1, Process::WNOHANG)
+        rescue Errno::ECHILD
+          nil
+        end
         if pid.nil?
           # no-op
         elsif (job = @jobs_by_pid[pid])
@@ -79,7 +84,7 @@ module Shell
         else
           warn "\n#{yellow("[WARN]")} No job found for child with PID #{pid}"
         end
-        Readline.refresh_line
+        @refresh_line.call
       end
     end
 
diff --git a/ruby/test/shell_test.rb b/ruby/test/shell_test.rb
index d53e56c..8a158f2 100644
--- a/ruby/test/shell_test.rb
+++ b/ruby/test/shell_test.rb
@@ -1,5 +1,9 @@
 require "minitest/autorun"
 require "etc"
+require "timeout"
+$LOAD_PATH.unshift(File.expand_path("..", __dir__))
+require_relative "../shell/job_control"
+require_relative "../shell/logger"
 
 class ShellTest < Minitest::Test
   TRIVIAL_SHELL_SCRIPT = "#!/bin/sh\ntrue".freeze
@@ -151,7 +155,21 @@ class ShellTest < Minitest::Test
   end
 
   def test_refreshes_readline_after_bg_execution
-    skip "unimplemented"
+    called = false
+    job_control = Shell::JobControl.new(
+      logger: Shell::Logger.instance,
+      refresh_line: -> { called = true }
+    )
+    previous = job_control.trap_sigchld
+    begin
+      job_control.exec_command("echo", ["hello"], background: true)
+      Timeout.timeout(2) do
+        sleep 0.01 until called
+      end
+      assert called
+    ensure
+      Signal.trap("CHLD", previous)
+    end
   end
 
   #########################