Implement CallTracker.thisFor().

spec/core/CallTrackerSpec.js

@@ -30,6 +30,18 @@ describe('CallTracker', function() {
     expect(callTracker.argsFor(1)).toEqual([0, 'foo']);
   });
 
+  it("tracks the 'this' object from each execution", function() {
+    var callTracker = new jasmineUnderTest.CallTracker();
+
+    var this0 = {},
+      this1 = {};
+    callTracker.track({ object: this0, args: [] });
+    callTracker.track({ object: this1, args: [] });
+
+    expect(callTracker.thisFor(0)).toBe(this0);
+    expect(callTracker.thisFor(1)).toBe(this1);
+  });
+
   it('returns any empty array when there was no call', function() {
     var callTracker = new jasmineUnderTest.CallTracker();
 

src/core/CallTracker.js

@@ -49,6 +49,19 @@ getJasmineRequireObj().CallTracker = function(j$) {
       return call ? call.args : [];
     };
 
+    /**
+     * Get the "this" object that was passed to a specific invocation of this spy.
+     * @name Spy#calls#thisFor
+     * @since 3.7.1
+     * @function
+     * @param {Integer} index The 0-based invocation index.
+     * @return {Object?}
+     */
+    this.thisFor = function(index) {
+      var call = calls[index];
+      return call ? call.object : undefined;
+    };
+
     /**
      * Get the raw calls array for this spy.
      * @name Spy#calls#all