Fix non-deterministic test in manager/unmanage

features/manager/unmanage.feature

@@ -2,7 +2,7 @@ Feature: manager client unmanagement
 
   Background:
     Given uhwm is running
-    And a window is mapped
+    And a window is managed
 
   Scenario: logs when a new client is unmanaged
     When the window requests to be unmapped

features/steps/x_steps.rb

@@ -1,11 +1,12 @@
-Given /^a window is mapped$/ do
-  x_window_map
-end
-
 Given /^a (\w+) window is mapped$/ do |ident|
   x_window_map ident: ident
 end
 
+Given /^a window is managed$/ do
+  x_window_map
+  uhwm_wait_output /manag.+#{x_window_name}/i
+end
+
 When /^I press the ([^ ]+) keys?$/ do |keys|
   x_key keys
 end