Add a setter for Object.prototype.should. Closes #86.

lib/chai/interface/should.js

@@ -10,7 +10,21 @@ module.exports = function (chai, util) {
   function loadShould () {
     // modify Object.prototype to have `should`
     Object.defineProperty(Object.prototype, 'should',
-      { set: function () {}
+      {
+        set: function (value) {
+          // See https://github.com/chaijs/chai/issues/86: this makes
+          // `whatever.should = someValue` actually set `someValue`, which is
+          // especially useful for `global.should = require('chai').should()`.
+          //
+          // Note that we have to use [[DefineProperty]] instead of [[Put]]
+          // since otherwise we would trigger this very setter!
+          Object.defineProperty(this, 'should', {
+            value: value,
+            enumerable: true,
+            configurable: true,
+            writable: true
+          });
+        }
       , get: function(){
           if (this instanceof String || this instanceof Number) {
             return new Assertion(this.constructor(this));

test/globalShould.js

@@ -0,0 +1,17 @@
+if (!chai) {
+  var chai = require('..');
+}
+
+suite('global should', function () {
+
+  test('works', function () {
+    global.should = chai.should();
+
+    try {
+        should.not.exist(undefined);
+    } finally {
+        delete global.should;
+    }
+  });
+
+});