Make toEqual matcher report the difference between objects

- Mismatches deep within object/array structures are pinpointed with a JsonPath-like syntax.

spec/core/matchers/DiffBuilderSpec.js

@@ -0,0 +1,47 @@
+describe("DiffBuilder", function() {
+  it("records the actual and expected objects", function() {
+    var diffBuilder = jasmineUnderTest.DiffBuilder();
+    diffBuilder.record({x: 'actual'}, {x: 'expected'});
+
+    expect(diffBuilder.getMessage()).toEqual("Expected Object({ x: 'actual' }) to equal Object({ x: 'expected' }).");
+  });
+
+  it("prints the path at which the difference was found", function() {
+    var diffBuilder = jasmineUnderTest.DiffBuilder();
+
+    diffBuilder.withPath('foo', function() {
+      diffBuilder.record({x: 'actual'}, {x: 'expected'});
+    });
+
+    expect(diffBuilder.getMessage()).toEqual("Expected $.foo = Object({ x: 'actual' }) to equal Object({ x: 'expected' }).");
+  });
+
+  it("prints multiple messages, separated by newlines", function() {
+    var diffBuilder = jasmineUnderTest.DiffBuilder();
+
+    diffBuilder.withPath('foo', function() {
+      diffBuilder.record(1, 2);
+    });
+
+    var message =
+      "Expected $.foo = 1 to equal 2.\n" +
+      "Expected 3 to equal 4.";
+
+    diffBuilder.record(3, 4);
+    expect(diffBuilder.getMessage()).toEqual(message);
+  });
+
+  it("allows customization of the message", function() {
+    var diffBuilder = jasmineUnderTest.DiffBuilder();
+
+    function darthVaderFormatter(actual, expected, path) {
+      return "I find your lack of " + expected + " disturbing. (was " + actual + ", at " + path + ")"
+    }
+
+    diffBuilder.withPath('x', function() {
+      diffBuilder.record('bar', 'foo', darthVaderFormatter);
+    });
+
+    expect(diffBuilder.getMessage()).toEqual("I find your lack of foo disturbing. (was bar, at $.x)");
+  });
+});