The best we can do with Open3 is always return true.

Open3 doesn't know the return value of executing the system command,
and some programs like to output to stderr during normal execution
(git clones/updates, nginx restarts, etc.) so stop returning false
if any lines are output to stderr since it's not correct.

lib/simpleton/command_runners/open3.rb

@@ -15,7 +15,7 @@ def self.run(host, command)
           puts err_lines.map { |error_line| "[#{host}]E #{error_line}" }.join
         end
 
-        err_lines.empty? ? true : false
+        true
       end
     end
   end

test/command_runners/open3_test.rb

@@ -96,17 +96,9 @@
     true
   end
 
-  asserts "that when there was error output, its return value" do
+  asserts "that its return value" do
     stub(::Open3).popen3("ssh", "#{host}", "#{command}") do
-      [ StringIO.new, StringIO.new, StringIO.new("error") ]
-    end
-
-    topic.run(host, command)
-  end.equals(false)
-
-  asserts "that when there was no error output, its return value" do
-    stub(::Open3).popen3("ssh", "#{host}", "#{command}") do
-      [ StringIO.new, StringIO.new, StringIO.new ]
+      [ StringIO.new, StringIO.new("output"), StringIO.new("error") ]
     end
 
     topic.run(host, command)