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 // Adding a debuggee more than once is redundant.

 var dbg = new Debugger;

 var g = newGlobal();

 var w = dbg.addDebuggee(g);

 assertEq(w instanceof Debugger.Object, true);

 function usual() {

     assertEq(dbg.hasDebuggee(g), true);

     assertEq(dbg.hasDebuggee(w), true);

     var arr = dbg.getDebuggees();

     assertEq(arr.length, 1);

     assertEq(arr[0], w);

 }

 usual();

 assertEq(dbg.addDebuggee(g), w);

 usual();

 assertEq(dbg.addDebuggee(w), w);

 usual();

 // Removing the debuggee once is enough.

 assertEq(dbg.removeDebuggee(g), undefined);

 assertEq(dbg.hasDebuggee(g), false);

 assertEq(dbg.getDebuggees().length, 0);