gecko/toolkit/mozapps/extensions/test/unit/test_bug474988.js

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 * The Original Code is mozilla.org code.
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 * The Initial Developer of the Original Code is
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var installListenerA = {};
var installListenerB = {};
var installListenerC = {};
var installListenerD = {};
var installListenerE = {};

function run_test() {
  createAppInfo("xpcshell@tests.mozilla.org", "XPCShell", "2", "1.9");
  startupEM();

  // Add some listeners
  do_check_eq(gEM.addInstallListener(installListenerA), 0);
  do_check_eq(gEM.addInstallListener(installListenerB), 1);
  do_check_eq(gEM.addInstallListener(installListenerC), 2);
  // Now stack is ABC

  // Should get back the same id if adding the same listener twice
  do_check_eq(gEM.addInstallListener(installListenerA), 0);
  do_check_eq(gEM.addInstallListener(installListenerB), 1);
  do_check_eq(gEM.addInstallListener(installListenerC), 2);
  // Stack is still ABC

  // Removing a listener shouldn't affect the id of the others
  gEM.removeInstallListenerAt(0);
  do_check_eq(gEM.addInstallListener(installListenerB), 1);
  do_check_eq(gEM.addInstallListener(installListenerC), 2);
  // Stack is .BC

  // Adding a new listener should still give a higher id than previously
  do_check_eq(gEM.addInstallListener(installListenerD), 3);
  // Stack is .BCD

  // Removing and re-adding the highest listener should give the same result.
  gEM.removeInstallListenerAt(3);
  do_check_eq(gEM.addInstallListener(installListenerE), 3);
  // Stack is .BCE

  do_check_eq(gEM.addInstallListener(installListenerD), 4);
  gEM.removeInstallListenerAt(3);
  do_check_eq(gEM.addInstallListener(installListenerE), 5);
  // Stack is .BC.DE

  // Stack should shorten down to the last listener
  gEM.removeInstallListenerAt(4);
  gEM.removeInstallListenerAt(5);
  do_check_eq(gEM.addInstallListener(installListenerD), 3);
  // Stack is .BCD

  // Stack should get down to 0
  gEM.removeInstallListenerAt(1);
  gEM.removeInstallListenerAt(2);
  gEM.removeInstallListenerAt(3);
  do_check_eq(gEM.addInstallListener(installListenerE), 0);
  gEM.removeInstallListenerAt(0);
  // Stack is empty
}