diff --git a/tests/framework/observe-expected.txt b/tests/framework/observe-expected.txt
new file mode 100644
index 00000000000..b58ed63e03a
--- /dev/null
+++ b/tests/framework/observe-expected.txt
@@ -0,0 +1,88 @@
+ERROR: Exception caught during observer callback: ouch 
+SOURCE: http://127.0.0.1:8000/sky/framework/sky-element/observe.sky:627
+ERROR: Exception caught during observer callback: ouch 
+SOURCE: http://127.0.0.1:8000/sky/framework/sky-element/observe.sky:627
+Running 80 tests
+ok 1 Path constructor throws
+ok 2 Path path validity
+ok 3 Path Paths are interned
+ok 4 Path null is empty path
+ok 5 Path undefined is empty path
+ok 6 Path Path.getValueFrom
+ok 7 Path Path.setValueFrom
+ok 8 Path Degenerate Values
+ok 9 Basic Tests Exception Doesnt Stop Notification
+ok 10 Basic Tests Can only open once
+ok 11 ObserverTransform Close Invokes Close
+ok 12 ObserverTransform valueFn/setValueFn
+ok 13 ObserverTransform valueFn - object literal
+ok 14 ObserverTransform CompoundObserver - valueFn reduction
+ok 15 PathObserver Tests Callback args
+ok 16 PathObserver Tests PathObserver.path
+ok 17 PathObserver Tests invalid
+ok 18 PathObserver Tests Optional target for callback
+ok 19 PathObserver Tests Delivery Until No Changes
+ok 20 PathObserver Tests Path disconnect
+ok 21 PathObserver Tests Path discardChanges
+ok 22 PathObserver Tests Path setValue
+ok 23 PathObserver Tests Degenerate Values
+ok 24 PathObserver Tests Path NaN
+ok 25 PathObserver Tests Path Set Value Back To Same
+ok 26 PathObserver Tests Path Triple Equals
+ok 27 PathObserver Tests Path Simple
+ok 28 PathObserver Tests Path Simple - path object
+ok 29 PathObserver Tests Path - root is initially null
+ok 30 PathObserver Tests Path With Indices
+ok 31 PathObserver Tests Path Observation
+ok 32 PathObserver Tests Path Set To Same As Prototype
+ok 33 PathObserver Tests Path Set Read Only
+ok 34 PathObserver Tests Path Set Shadows
+ok 35 PathObserver Tests Delete With Same Value On Prototype
+ok 36 PathObserver Tests Delete With Different Value On Prototype
+ok 37 PathObserver Tests Value Change On Prototype
+ok 38 PathObserver Tests Delete Of Non Configurable
+ok 39 PathObserver Tests Notify
+ok 40 PathObserver Tests issue-161
+ok 41 PathObserver Tests object cycle
+ok 42 CompoundObserver Tests Simple
+ok 43 CompoundObserver Tests reportChangesOnOpen
+ok 44 CompoundObserver Tests Degenerate Values
+ok 45 CompoundObserver Tests valueFn - return object literal
+ok 46 CompoundObserver Tests reset
+ok 47 CompoundObserver Tests Heterogeneous
+ok 48 ArrayObserver Tests Optional target for callback
+ok 49 ArrayObserver Tests Delivery Until No Changes
+ok 50 ArrayObserver Tests Array disconnect
+ok 51 ArrayObserver Tests Array discardChanges
+ok 52 ArrayObserver Tests Array
+ok 53 ArrayObserver Tests Array observe non-array throws
+ok 54 ArrayObserver Tests Array Set Same
+ok 55 ArrayObserver Tests Array Splice
+ok 56 ArrayObserver Tests Array Splice Truncate And Expand With Length
+ok 57 ArrayObserver Tests Array Splice Delete Too Many
+ok 58 ArrayObserver Tests Array Length
+ok 59 ArrayObserver Tests Array Push
+ok 60 ArrayObserver Tests Array Pop
+ok 61 ArrayObserver Tests Array Shift
+ok 62 ArrayObserver Tests Array Unshift
+ok 63 ArrayObserver Tests Array Tracker Contained
+ok 64 ArrayObserver Tests Array Tracker Delete Empty
+ok 65 ArrayObserver Tests Array Tracker Right Non Overlap
+ok 66 ArrayObserver Tests Array Tracker Left Non Overlap
+ok 67 ArrayObserver Tests Array Tracker Right Adjacent
+ok 68 ArrayObserver Tests Array Tracker Left Adjacent
+ok 69 ArrayObserver Tests Array Tracker Right Overlap
+ok 70 ArrayObserver Tests Array Tracker Left Overlap
+ok 71 ArrayObserver Tests Array Tracker Prefix And Suffix One In
+ok 72 ArrayObserver Tests Array Tracker Shift One
+ok 73 ArrayObserver Tests Array Tracker Update Delete
+ok 74 ArrayObserver Tests Array Tracker Update After Delete
+ok 75 ArrayObserver Tests Array Tracker Delete Mid Array
+ok 76 ArrayObserver Tests Array Random Case 1
+ok 77 ArrayObserver Tests Array Random Case 2
+ok 78 ArrayObserver Tests Array Random Case 3
+ok 79 ArrayObserver Tests Array Tracker Fuzzer
+ok 80 ArrayObserver Tests Array Tracker No Proxies Edits
+80 tests
+80 pass
+0 fail
diff --git a/tests/framework/observe.sky b/tests/framework/observe.sky
new file mode 100644
index 00000000000..4ba41e7dae3
--- /dev/null
+++ b/tests/framework/observe.sky
@@ -0,0 +1,1872 @@
+<html>
+<link rel="import" href="../resources/chai.sky" />
+<link rel="import" href="../resources/mocha.sky" />
+<link rel="import" href="/sky/framework/sky-element/observe.sky" as="observe" />
+
+<script>
+
+var Path = observe.Path;
+var PathObserver = observe.PathObserver;
+var ArrayObserver = observe.ArrayObserver;
+var ObjectObserver = observe.ObjectObserver;
+var CompoundObserver = observe.CompoundObserver;
+var ObserverTransform = observe.ObserverTransform;
+
+var observer;
+var callbackArgs = undefined;
+var callbackInvoked = false;
+
+function then(fn) {
+  setTimeout(function() {
+    fn();
+  }, 0);
+
+  return {
+    then: function(next) {
+      return then(next);
+    }
+  };
+}
+
+function noop() {}
+
+function callback() {
+  callbackArgs = Array.prototype.slice.apply(arguments);
+  callbackInvoked = true;
+}
+
+function doSetup() {}
+function doTeardown() {
+  callbackInvoked = false;
+  callbackArgs = undefined;
+}
+
+function assertNoChanges() {
+  if (observer)
+    observer.deliver();
+  assert.isFalse(callbackInvoked);
+  assert.isUndefined(callbackArgs);
+}
+
+function assertPathChanges(expectNewValue, expectOldValue, dontDeliver) {
+  if (!dontDeliver)
+    observer.deliver();
+
+  assert.isTrue(callbackInvoked);
+
+  var newValue = callbackArgs[0];
+  var oldValue = callbackArgs[1];
+  assert.deepEqual(expectNewValue, newValue);
+  assert.deepEqual(expectOldValue, oldValue);
+
+  if (!dontDeliver) {
+    assert.isTrue(window.dirtyCheckCycleCount === undefined ||
+                  window.dirtyCheckCycleCount === 1);
+  }
+
+  callbackArgs = undefined;
+  callbackInvoked = false;
+}
+
+function assertCompoundPathChanges(expectNewValues, expectOldValues,
+                                   expectObserved, dontDeliver) {
+  if (!dontDeliver)
+    observer.deliver();
+
+  assert.isTrue(callbackInvoked);
+
+  var newValues = callbackArgs[0];
+  var oldValues = callbackArgs[1];
+  var observed = callbackArgs[2];
+  assert.deepEqual(expectNewValues, newValues);
+  assert.deepEqual(expectOldValues, oldValues);
+  assert.deepEqual(expectObserved, observed);
+
+  if (!dontDeliver) {
+    assert.isTrue(window.dirtyCheckCycleCount === undefined ||
+                  window.dirtyCheckCycleCount === 1);
+  }
+
+  callbackArgs = undefined;
+  callbackInvoked = false;
+}
+
+var createObject = ('__proto__' in {}) ?
+  function(obj) { return obj; } :
+  function(obj) {
+    var proto = obj.__proto__;
+    if (!proto)
+      return obj;
+    var newObject = Object.create(proto);
+    Object.getOwnPropertyNames(obj).forEach(function(name) {
+      Object.defineProperty(newObject, name,
+                           Object.getOwnPropertyDescriptor(obj, name));
+    });
+    return newObject;
+  };
+
+function assertPath(pathString, expectKeys, expectSerialized) {
+  var path = Path.get(pathString);
+  if (!expectKeys) {
+    assert.isFalse(path.valid);
+    return;
+  }
+
+  assert.deepEqual(Array.prototype.slice.apply(path), expectKeys);
+  assert.strictEqual(path.toString(), expectSerialized);
+}
+
+function assertInvalidPath(pathString) {
+  assertPath(pathString);
+}
+
+describe('Path', function() {
+  it('constructor throws', function() {
+    assert.throws(function() {
+      new Path('foo')
+    });
+  });
+
+  it('path validity', function() {
+    // invalid path get value is always undefined
+    var p = Path.get('a b');
+    assert.isFalse(p.valid);
+    assert.isUndefined(p.getValueFrom({ a: { b: 2 }}));
+
+    assertPath('', [], '');
+    assertPath(' ', [], '');
+    assertPath(null, [], '');
+    assertPath(undefined, [], '');
+    assertPath('a', ['a'], 'a');
+    assertPath('a.b', ['a', 'b'], 'a.b');
+    assertPath('a. b', ['a', 'b'], 'a.b');
+    assertPath('a .b', ['a', 'b'], 'a.b');
+    assertPath('a . b', ['a', 'b'], 'a.b');
+    assertPath(' a . b ', ['a', 'b'], 'a.b');
+    assertPath('a[0]', ['a', '0'], 'a[0]');
+    assertPath('a [0]', ['a', '0'], 'a[0]');
+    assertPath('a[0][1]', ['a', '0', '1'], 'a[0][1]');
+    assertPath('a [ 0 ] [ 1 ] ', ['a', '0', '1'], 'a[0][1]');
+    assertPath('[1234567890] ', ['1234567890'], '[1234567890]');
+    assertPath(' [1234567890] ', ['1234567890'], '[1234567890]');
+    assertPath('opt0', ['opt0'], 'opt0');
+    assertPath('$foo.$bar._baz', ['$foo', '$bar', '_baz'], '$foo.$bar._baz');
+    assertPath('foo["baz"]', ['foo', 'baz'], 'foo.baz');
+    assertPath('foo["b\\"az"]', ['foo', 'b"az'], 'foo["b\\"az"]');
+    assertPath("foo['b\\'az']", ['foo', "b'az"], 'foo["b\'az"]');
+    assertPath(['a', 'b'], ['a', 'b'], 'a.b');
+    assertPath([''], [''], '[""]');
+
+    function Foo(val) { this.val = val; }
+    Foo.prototype.toString = function() { return 'Foo' + this.val; };
+    assertPath([new Foo('a'), new Foo('b')], ['Fooa', 'Foob'], 'Fooa.Foob');
+
+    assertInvalidPath('.');
+    assertInvalidPath(' . ');
+    assertInvalidPath('..');
+    assertInvalidPath('a[4');
+    assertInvalidPath('a.b.');
+    assertInvalidPath('a,b');
+    assertInvalidPath('a["foo]');
+    assertInvalidPath('[0x04]');
+    assertInvalidPath('[0foo]');
+    assertInvalidPath('[foo-bar]');
+    assertInvalidPath('foo-bar');
+    assertInvalidPath('42');
+    assertInvalidPath('a[04]');
+    assertInvalidPath(' a [ 04 ]');
+    assertInvalidPath('  42   ');
+    assertInvalidPath('foo["bar]');
+    assertInvalidPath("foo['bar]");
+  });
+
+  it('Paths are interned', function() {
+    var p = Path.get('foo.bar');
+    var p2 = Path.get('foo.bar');
+    assert.strictEqual(p, p2);
+
+    var p3 = Path.get('');
+    var p4 = Path.get('');
+    assert.strictEqual(p3, p4);
+  });
+
+  it('null is empty path', function() {
+    assert.strictEqual(Path.get(''), Path.get(null));
+  });
+
+  it('undefined is empty path', function() {
+    assert.strictEqual(Path.get(undefined), Path.get(null));
+  });
+
+  it('Path.getValueFrom', function() {
+    var obj = {
+      a: {
+        b: {
+          c: 1
+        }
+      }
+    };
+
+    var p1 = Path.get('a');
+    var p2 = Path.get('a.b');
+    var p3 = Path.get('a.b.c');
+
+    assert.strictEqual(obj.a, p1.getValueFrom(obj));
+    assert.strictEqual(obj.a.b, p2.getValueFrom(obj));
+    assert.strictEqual(1, p3.getValueFrom(obj));
+
+    obj.a.b.c = 2;
+    assert.strictEqual(2, p3.getValueFrom(obj));
+
+    obj.a.b = {
+      c: 3
+    };
+    assert.strictEqual(3, p3.getValueFrom(obj));
+
+    obj.a = {
+      b: 4
+    };
+    assert.strictEqual(undefined, p3.getValueFrom(obj));
+    assert.strictEqual(4, p2.getValueFrom(obj));
+  });
+
+  it('Path.setValueFrom', function() {
+    var obj = {};
+    var p2 = Path.get('bar');
+
+    Path.get('foo').setValueFrom(obj, 3);
+    assert.equal(3, obj.foo);
+
+    var bar = { baz: 3 };
+
+    Path.get('bar').setValueFrom(obj, bar);
+    assert.equal(bar, obj.bar);
+
+    var p = Path.get('bar.baz.bat');
+    p.setValueFrom(obj, 'not here');
+    assert.equal(undefined, p.getValueFrom(obj));
+  });
+
+  it('Degenerate Values', function() {
+    var emptyPath = Path.get();
+    var foo = {};
+
+    assert.equal(null, emptyPath.getValueFrom(null));
+    assert.equal(foo, emptyPath.getValueFrom(foo));
+    assert.equal(3, emptyPath.getValueFrom(3));
+    assert.equal(undefined, Path.get('a').getValueFrom(undefined));
+  });
+});
+
+describe('Basic Tests', function() {
+
+  it('Exception Doesnt Stop Notification', function() {
+    var model = [1];
+    var count = 0;
+
+    var observer2 = new PathObserver(model, '[0]');
+    observer2.open(function() {
+      count++;
+      throw 'ouch';
+    });
+
+    var observer3 = new ArrayObserver(model);
+    observer3.open(function() {
+      count++;
+      throw 'ouch';
+    });
+
+    model[0] = 2;
+    model[1] = 2;
+
+    observer2.deliver();
+    observer3.deliver();
+
+    assert.equal(2, count);
+
+    observer2.close();
+    observer3.close();
+  });
+
+  it('Can only open once', function() {
+    observer = new PathObserver({ id: 1 }, 'id');
+    observer.open(callback);
+    assert.throws(function() {
+      observer.open(callback);
+    });
+    observer.close();
+
+    observer = new CompoundObserver();
+    observer.open(callback);
+    assert.throws(function() {
+      observer.open(callback);
+    });
+    observer.close();
+
+    observer = new ArrayObserver([], 'id');
+    observer.open(callback);
+    assert.throws(function() {
+      observer.open(callback);
+    });
+    observer.close();
+
+  });
+
+});
+
+describe('ObserverTransform', function() {
+
+  it('Close Invokes Close', function() {
+    var count = 0;
+    var observer = {
+      open: function() {},
+      close: function() { count++; }
+    };
+
+    var observer = new ObserverTransform(observer);
+    observer.open();
+    observer.close();
+    assert.strictEqual(1, count);
+  });
+
+  it('valueFn/setValueFn', function() {
+    var obj = { foo: 1 };
+
+    function valueFn(value) { return value * 2; }
+
+    function setValueFn(value) { return value / 2; }
+
+    observer = new ObserverTransform(new PathObserver(obj, 'foo'),
+                                     valueFn,
+                                     setValueFn);
+    observer.open(callback);
+
+    obj.foo = 2;
+
+    assert.strictEqual(4, observer.discardChanges());
+    assertNoChanges();
+
+    observer.setValue(2);
+    assert.strictEqual(obj.foo, 1);
+    assertPathChanges(2, 4);
+
+    obj.foo = 10;
+    assertPathChanges(20, 2);
+
+    observer.close();
+  });
+
+  it('valueFn - object literal', function() {
+    var model = {};
+
+    function valueFn(value) {
+      return [ value ];
+    }
+
+    observer = new ObserverTransform(new PathObserver(model, 'foo'), valueFn);
+    observer.open(callback);
+
+    model.foo = 1;
+    assertPathChanges([1], [undefined]);
+
+    model.foo = 3;
+    assertPathChanges([3], [1]);
+
+    observer.close();
+  });
+
+  it('CompoundObserver - valueFn reduction', function() {
+    var model = { a: 1, b: 2, c: 3 };
+
+    function valueFn(values) {
+      return values.reduce(function(last, cur) {
+        return typeof cur === 'number' ? last + cur : undefined;
+      }, 0);
+    }
+
+    var compound = new CompoundObserver();
+    compound.addPath(model, 'a');
+    compound.addPath(model, 'b');
+    compound.addPath(model, Path.get('c'));
+
+    observer = new ObserverTransform(compound, valueFn);
+    assert.strictEqual(6, observer.open(callback));
+
+    model.a = -10;
+    model.b = 20;
+    model.c = 30;
+    assertPathChanges(40, 6);
+
+    observer.close();
+  });
+})
+
+describe('PathObserver Tests', function() {
+
+  beforeEach(doSetup);
+
+  afterEach(doTeardown);
+
+  it('Callback args', function() {
+    var obj = {
+      foo: 'bar'
+    };
+
+    var path = Path.get('foo');
+    var observer = new PathObserver(obj, path);
+
+    var args;
+    observer.open(function() {
+      args = Array.prototype.slice.apply(arguments);
+    });
+
+    obj.foo = 'baz';
+    observer.deliver();
+    assert.strictEqual(args.length, 3);
+    assert.strictEqual(args[0], 'baz');
+    assert.strictEqual(args[1], 'bar');
+    assert.strictEqual(args[2], observer);
+    assert.strictEqual(args[2].path, path);
+    observer.close();
+  });
+
+  it('PathObserver.path', function() {
+    var obj = {
+      foo: 'bar'
+    };
+
+    var path = Path.get('foo');
+    var observer = new PathObserver(obj, 'foo');
+    assert.strictEqual(observer.path, Path.get('foo'));
+  });
+
+
+  it('invalid', function() {
+    var observer = new PathObserver({ a: { b: 1 }} , 'a b');
+    observer.open(callback);
+    assert.strictEqual(undefined, observer.value);
+    observer.deliver();
+    assert.isFalse(callbackInvoked);
+  });
+
+  it('Optional target for callback', function() {
+    var target = {
+      changed: function(value, oldValue) {
+        this.called = true;
+      }
+    };
+    var obj = { foo: 1 };
+    var observer = new PathObserver(obj, 'foo');
+    observer.open(target.changed, target);
+    obj.foo = 2;
+    observer.deliver();
+    assert.isTrue(target.called);
+
+    observer.close();
+  });
+
+  it('Delivery Until No Changes', function() {
+    var obj = { foo: { bar: 5 }};
+    var callbackCount = 0;
+    var observer = new PathObserver(obj, 'foo . bar');
+    observer.open(function() {
+      callbackCount++;
+      if (!obj.foo.bar)
+        return;
+
+      obj.foo.bar--;
+    });
+
+    obj.foo.bar--;
+    observer.deliver();
+
+    assert.equal(5, callbackCount);
+
+    observer.close();
+  });
+
+  it('Path disconnect', function() {
+    var arr = {};
+
+    arr.foo = 'bar';
+    observer = new PathObserver(arr, 'foo');
+    observer.open(callback);
+    arr.foo = 'baz';
+
+    assertPathChanges('baz', 'bar');
+    arr.foo = 'bar';
+
+    observer.close();
+
+    arr.foo = 'boo';
+    assertNoChanges();
+  });
+
+  it('Path discardChanges', function() {
+    var arr = {};
+
+    arr.foo = 'bar';
+    observer = new PathObserver(arr, 'foo');
+    observer.open(callback);
+    arr.foo = 'baz';
+
+    assertPathChanges('baz', 'bar');
+
+    arr.foo = 'bat';
+    observer.discardChanges();
+    assertNoChanges();
+
+    arr.foo = 'bag';
+    assertPathChanges('bag', 'bat');
+    observer.close();
+  });
+
+  it('Path setValue', function() {
+    var obj = {};
+
+    obj.foo = 'bar';
+    observer = new PathObserver(obj, 'foo');
+    observer.open(callback);
+    obj.foo = 'baz';
+
+    observer.setValue('bat');
+    assert.strictEqual(obj.foo, 'bat');
+    assertPathChanges('bat', 'bar');
+
+    observer.setValue('bot');
+    observer.discardChanges();
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Degenerate Values', function() {
+    var emptyPath = Path.get();
+    observer = new PathObserver(null, '');
+    observer.open(callback);
+    assert.equal(null, observer.value);
+    observer.close();
+
+    var foo = {};
+    observer = new PathObserver(foo, '');
+    assert.equal(foo, observer.open(callback));
+    observer.close();
+
+    observer = new PathObserver(3, '');
+    assert.equal(3, observer.open(callback));
+    observer.close();
+
+    observer = new PathObserver(undefined, 'a');
+    assert.equal(undefined, observer.open(callback));
+    observer.close();
+
+    var bar = { id: 23 };
+    observer = new PathObserver(undefined, 'a/3!');
+    assert.equal(undefined, observer.open(callback));
+    observer.close();
+  });
+
+  it('Path NaN', function() {
+    var foo = { val: 1 };
+    observer = new PathObserver(foo, 'val');
+    observer.open(callback);
+    foo.val = 0/0;
+
+    // Can't use assertSummary because deepEqual() will fail with NaN
+    observer.deliver();
+    assert.isTrue(callbackInvoked);
+    assert.isTrue(isNaN(callbackArgs[0]));
+    assert.strictEqual(1, callbackArgs[1]);
+    observer.close();
+  });
+
+  it('Path Set Value Back To Same', function() {
+    var obj = {};
+    var path = Path.get('foo');
+
+    path.setValueFrom(obj, 3);
+    assert.equal(3, obj.foo);
+
+    observer = new PathObserver(obj, 'foo');
+    assert.equal(3, observer.open(callback));
+
+    path.setValueFrom(obj, 2);
+    assert.equal(2, observer.discardChanges());
+
+    path.setValueFrom(obj, 3);
+    assert.equal(3, observer.discardChanges());
+
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Path Triple Equals', function() {
+    var model = { };
+
+    observer = new PathObserver(model, 'foo');
+    observer.open(callback);
+
+    model.foo = null;
+    assertPathChanges(null, undefined);
+
+    model.foo = undefined;
+    assertPathChanges(undefined, null);
+
+    observer.close();
+  });
+
+  it('Path Simple', function() {
+    var model = { };
+
+    observer = new PathObserver(model, 'foo');
+    observer.open(callback);
+
+    model.foo = 1;
+    assertPathChanges(1, undefined);
+
+    model.foo = 2;
+    assertPathChanges(2, 1);
+
+    delete model.foo;
+    assertPathChanges(undefined, 2);
+
+    observer.close();
+  });
+
+  it('Path Simple - path object', function() {
+    var model = { };
+
+    var path = Path.get('foo');
+    observer = new PathObserver(model, path);
+    observer.open(callback);
+
+    model.foo = 1;
+    assertPathChanges(1, undefined);
+
+    model.foo = 2;
+    assertPathChanges(2, 1);
+
+    delete model.foo;
+    assertPathChanges(undefined, 2);
+
+    observer.close();
+  });
+
+  it('Path - root is initially null', function(done) {
+    var model = { };
+
+    var path = Path.get('foo');
+    observer = new PathObserver(model, 'foo.bar');
+    observer.open(callback);
+
+    model.foo = { };
+    then(function() {
+      model.foo.bar = 1;
+
+    }).then(function() {
+      assertPathChanges(1, undefined, true);
+
+      observer.close();
+      done();
+    });
+  });
+
+  it('Path With Indices', function() {
+    var model = [];
+
+    observer = new PathObserver(model, '[0]');
+    observer.open(callback);
+
+    model.push(1);
+    assertPathChanges(1, undefined);
+
+    observer.close();
+  });
+
+  it('Path Observation', function() {
+    var model = {
+      a: {
+        b: {
+          c: 'hello, world'
+        }
+      }
+    };
+
+    observer = new PathObserver(model, 'a.b.c');
+    observer.open(callback);
+
+    model.a.b.c = 'hello, mom';
+    assertPathChanges('hello, mom', 'hello, world');
+
+    model.a.b = {
+      c: 'hello, dad'
+    };
+    assertPathChanges('hello, dad', 'hello, mom');
+
+    model.a = {
+      b: {
+        c: 'hello, you'
+      }
+    };
+    assertPathChanges('hello, you', 'hello, dad');
+
+    model.a.b = 1;
+    assertPathChanges(undefined, 'hello, you');
+
+    // Stop observing
+    observer.close();
+
+    model.a.b = {c: 'hello, back again -- but not observing'};
+    assertNoChanges();
+
+    // Resume observing
+    observer = new PathObserver(model, 'a.b.c');
+    observer.open(callback);
+
+    model.a.b.c = 'hello. Back for reals';
+    assertPathChanges('hello. Back for reals',
+        'hello, back again -- but not observing');
+
+    observer.close();
+  });
+
+  it('Path Set To Same As Prototype', function() {
+    var model = createObject({
+      __proto__: {
+        id: 1
+      }
+    });
+
+    observer = new PathObserver(model, 'id');
+    observer.open(callback);
+    model.id = 1;
+
+    assertNoChanges();
+    observer.close();
+  });
+
+  it('Path Set Read Only', function() {
+    var model = {};
+    Object.defineProperty(model, 'x', {
+      configurable: true,
+      writable: false,
+      value: 1
+    });
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+
+    assert.throws(function() {
+      model.x = 2;
+    });
+
+    assertNoChanges();
+    observer.close();
+  });
+
+  it('Path Set Shadows', function() {
+    var model = createObject({
+      __proto__: {
+        x: 1
+      }
+    });
+
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+    model.x = 2;
+    assertPathChanges(2, 1);
+    observer.close();
+  });
+
+  it('Delete With Same Value On Prototype', function() {
+    var model = createObject({
+      __proto__: {
+        x: 1,
+      },
+      x: 1
+    });
+
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+    delete model.x;
+    assertNoChanges();
+    observer.close();
+  });
+
+  it('Delete With Different Value On Prototype', function() {
+    var model = createObject({
+      __proto__: {
+        x: 1,
+      },
+      x: 2
+    });
+
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+    delete model.x;
+    assertPathChanges(1, 2);
+    observer.close();
+  });
+
+  it('Value Change On Prototype', function() {
+    var proto = {
+      x: 1
+    }
+    var model = createObject({
+      __proto__: proto
+    });
+
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+    model.x = 2;
+    assertPathChanges(2, 1);
+
+    delete model.x;
+    assertPathChanges(1, 2);
+
+    proto.x = 3;
+    assertPathChanges(3, 1);
+    observer.close();
+  });
+
+  // FIXME: Need test of observing change on proto.
+
+  it('Delete Of Non Configurable', function() {
+    var model = {};
+    Object.defineProperty(model, 'x', {
+      configurable: false,
+      value: 1
+    });
+
+    observer = new PathObserver(model, 'x');
+    observer.open(callback);
+
+    assert.throws(function() {
+      delete model.x;
+    });
+
+    assertNoChanges();
+    observer.close();
+  });
+
+  it('Notify', function() {
+    if (typeof Object.getNotifier !== 'function')
+      return;
+
+    var model = {
+      a: {}
+    }
+
+    var _b = 2;
+
+    Object.defineProperty(model.a, 'b', {
+      get: function() { return _b; },
+      set: function(b) {
+        Object.getNotifier(this).notify({
+          type: 'update',
+          name: 'b',
+          oldValue: _b
+        });
+
+        _b = b;
+      }
+    });
+
+    observer = new PathObserver(model, 'a.b');
+    observer.open(callback);
+    _b = 3;
+    assertPathChanges(3, 2);
+
+    model.a.b = 4; // will be observed.
+    assertPathChanges(4, 3);
+
+    observer.close();
+  });
+
+  it('issue-161', function(done) {
+    var model = { model: 'model' };
+    var ob1 = new PathObserver(model, 'obj.bar');
+    var called = false
+    ob1.open(function() {
+      called = true;
+    });
+
+    var obj2 = new PathObserver(model, 'obj');
+    obj2.open(function() {
+      model.obj.bar = true;
+    });
+
+    model.obj = { 'obj': 'obj' };
+    model.obj.foo = true;
+
+    then(function() {
+      assert.strictEqual(called, true);
+      done();
+    });
+  });
+
+  it('object cycle', function(done) {
+    var model = { a: {}, c: 1 };
+    model.a.b = model;
+
+    var called = 0;
+    new PathObserver(model, 'a.b.c').open(function() {
+      called++;
+    });
+
+    // This change should be detected, even though it's a change to the root
+    // object and isn't a change to `a`.
+    model.c = 42;
+
+    then(function() {
+      assert.equal(called, 1);
+      done();
+    });
+  });
+
+});
+
+
+describe('CompoundObserver Tests', function() {
+
+  beforeEach(doSetup);
+
+  afterEach(doTeardown);
+
+  it('Simple', function() {
+    var model = { a: 1, b: 2, c: 3 };
+
+    observer = new CompoundObserver();
+    observer.addPath(model, 'a');
+    observer.addPath(model, 'b');
+    observer.addPath(model, Path.get('c'));
+    observer.open(callback);
+    assertNoChanges();
+
+    var observerCallbackArg = [model, Path.get('a'),
+                               model, Path.get('b'),
+                               model, Path.get('c')];
+    model.a = -10;
+    model.b = 20;
+    model.c = 30;
+    assertCompoundPathChanges([-10, 20, 30], [1, 2, 3],
+                              observerCallbackArg);
+
+    model.a = 'a';
+    model.c = 'c';
+    assertCompoundPathChanges(['a', 20, 'c'], [-10,, 30],
+                              observerCallbackArg);
+
+    model.a = 2;
+    model.b = 3;
+    model.c = 4;
+
+    assertCompoundPathChanges([2, 3, 4], ['a', 20, 'c'],
+                              observerCallbackArg);
+
+    model.a = 'z';
+    model.b = 'y';
+    model.c = 'x';
+    assert.deepEqual(['z', 'y', 'x'], observer.discardChanges());
+    assertNoChanges();
+
+    assert.strictEqual('z', model.a);
+    assert.strictEqual('y', model.b);
+    assert.strictEqual('x', model.c);
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('reportChangesOnOpen', function() {
+    var model = { a: 1, b: 2, c: 3 };
+
+    observer = new CompoundObserver(true);
+    observer.addPath(model, 'a');
+    observer.addPath(model, 'b');
+    observer.addPath(model, Path.get('c'));
+
+    model.a = -10;
+    model.b = 20;
+    observer.open(callback);
+    var observerCallbackArg = [model, Path.get('a'),
+                               model, Path.get('b'),
+                               model, Path.get('c')];
+    assertCompoundPathChanges([-10, 20, 3], [1, 2, ],
+                              observerCallbackArg, true);
+    observer.close();
+  });
+
+  it('Degenerate Values', function() {
+    var model = {};
+    observer = new CompoundObserver();
+    observer.addPath({}, '.'); // invalid path
+    observer.addPath('obj-value', ''); // empty path
+    observer.addPath({}, 'foo'); // unreachable
+    observer.addPath(3, 'bar'); // non-object with non-empty path
+    var values = observer.open(callback);
+    assert.strictEqual(4, values.length);
+    assert.strictEqual(undefined, values[0]);
+    assert.strictEqual('obj-value', values[1]);
+    assert.strictEqual(undefined, values[2]);
+    assert.strictEqual(undefined, values[3]);
+    observer.close();
+  });
+
+  it('valueFn - return object literal', function() {
+    var model = { a: 1};
+
+    function valueFn(values) {
+      return {};
+    }
+
+    observer = new CompoundObserver(valueFn);
+
+    observer.addPath(model, 'a');
+    observer.open(callback);
+    model.a = 2;
+
+    observer.deliver();
+    assert.isTrue(window.dirtyCheckCycleCount === undefined ||
+                  window.dirtyCheckCycleCount === 1);
+    observer.close();
+  });
+
+  it('reset', function() {
+    var model = { a: 1, b: 2, c: 3 };
+    var callCount = 0;
+    function callback() {
+      callCount++;
+    }
+
+    observer = new CompoundObserver();
+
+    observer.addPath(model, 'a');
+    observer.addPath(model, 'b');
+    assert.deepEqual([1, 2], observer.open(callback));
+
+    model.a = 2;
+    observer.deliver();
+    assert.strictEqual(1, callCount);
+
+    model.b = 3;
+    observer.deliver();
+    assert.strictEqual(2, callCount);
+
+    model.c = 4;
+    observer.deliver();
+    assert.strictEqual(2, callCount);
+
+    observer.startReset();
+    observer.addPath(model, 'b');
+    observer.addPath(model, 'c');
+    assert.deepEqual([3, 4], observer.finishReset())
+
+    model.a = 3;
+    observer.deliver();
+    assert.strictEqual(2, callCount);
+
+    model.b = 4;
+    observer.deliver();
+    assert.strictEqual(3, callCount);
+
+    model.c = 5;
+    observer.deliver();
+    assert.strictEqual(4, callCount);
+
+    observer.close();
+  });
+
+  it('Heterogeneous', function() {
+    var model = { a: 1, b: 2 };
+    var otherModel = { c: 3 };
+
+    function valueFn(value) { return value * 2; }
+    function setValueFn(value) { return value / 2; }
+
+    var compound = new CompoundObserver;
+    compound.addPath(model, 'a');
+    compound.addObserver(new ObserverTransform(new PathObserver(model, 'b'),
+                                               valueFn, setValueFn));
+    compound.addObserver(new PathObserver(otherModel, 'c'));
+
+    function combine(values) {
+      return values[0] + values[1] + values[2];
+    };
+    observer = new ObserverTransform(compound, combine);
+    assert.strictEqual(8, observer.open(callback));
+
+    model.a = 2;
+    model.b = 4;
+    assertPathChanges(13, 8);
+
+    model.b = 10;
+    otherModel.c = 5;
+    assertPathChanges(27, 13);
+
+    model.a = 20;
+    model.b = 1;
+    otherModel.c = 5;
+    assertNoChanges();
+
+    observer.close();
+  })
+});
+
+describe('ArrayObserver Tests', function() {
+
+  beforeEach(doSetup);
+
+  afterEach(doTeardown);
+
+  function ensureNonSparse(arr) {
+    for (var i = 0; i < arr.length; i++) {
+      if (i in arr)
+        continue;
+      arr[i] = undefined;
+    }
+  }
+
+  function assertArrayChanges(expectSplices) {
+    observer.deliver();
+    var splices = callbackArgs[0];
+
+    assert.isTrue(callbackInvoked);
+
+    splices.forEach(function(splice) {
+      ensureNonSparse(splice.removed);
+    });
+
+    expectSplices.forEach(function(splice) {
+      ensureNonSparse(splice.removed);
+    });
+
+    assert.deepEqual(expectSplices, splices);
+    callbackArgs = undefined;
+    callbackInvoked = false;
+  }
+
+  function applySplicesAndAssertDeepEqual(orig, copy) {
+    observer.deliver();
+    if (callbackInvoked) {
+      var splices = callbackArgs[0];
+      ArrayObserver.applySplices(copy, orig, splices);
+    }
+
+    ensureNonSparse(orig);
+    ensureNonSparse(copy);
+    assert.deepEqual(orig, copy);
+    callbackArgs = undefined;
+    callbackInvoked = false;
+  }
+
+  function assertEditDistance(orig, expectDistance) {
+    observer.deliver();
+    var splices = callbackArgs[0];
+    var actualDistance = 0;
+
+    if (callbackInvoked) {
+      splices.forEach(function(splice) {
+        actualDistance += splice.addedCount + splice.removed.length;
+      });
+    }
+
+    assert.deepEqual(expectDistance, actualDistance);
+    callbackArgs = undefined;
+    callbackInvoked = false;
+  }
+
+  function arrayMutationTest(arr, operations) {
+    var copy = arr.slice();
+    observer = new ArrayObserver(arr);
+    observer.open(callback);
+    operations.forEach(function(op) {
+      switch(op.name) {
+        case 'delete':
+          delete arr[op.index];
+          break;
+
+        case 'update':
+          arr[op.index] = op.value;
+          break;
+
+        default:
+          arr[op.name].apply(arr, op.args);
+          break;
+      }
+    });
+
+    applySplicesAndAssertDeepEqual(arr, copy);
+    observer.close();
+  }
+
+  it('Optional target for callback', function() {
+    var target = {
+      changed: function(splices) {
+        this.called = true;
+      }
+    };
+    var obj = [];
+    var observer = new ArrayObserver(obj);
+    observer.open(target.changed, target);
+    obj.length = 1;
+    observer.deliver();
+    assert.isTrue(target.called);
+    observer.close();
+  });
+
+  it('Delivery Until No Changes', function() {
+    var arr = [0, 1, 2, 3, 4];
+    var callbackCount = 0;
+    var observer = new ArrayObserver(arr);
+    observer.open(function() {
+      callbackCount++;
+      arr.shift();
+    });
+
+    arr.shift();
+    observer.deliver();
+
+    assert.equal(5, callbackCount);
+
+    observer.close();
+  });
+
+  it('Array disconnect', function() {
+    var arr = [ 0 ];
+
+    observer = new ArrayObserver(arr);
+    observer.open(callback);
+
+    arr[0] = 1;
+
+    assertArrayChanges([{
+      index: 0,
+      removed: [0],
+      addedCount: 1
+    }]);
+
+    observer.close();
+    arr[1] = 2;
+    assertNoChanges();
+  });
+
+  it('Array discardChanges', function() {
+    var arr = [];
+
+    arr.push(1);
+    observer = new ArrayObserver(arr);
+    observer.open(callback);
+    arr.push(2);
+
+    assertArrayChanges([{
+      index: 1,
+      removed: [],
+      addedCount: 1
+    }]);
+
+    arr.push(3);
+    observer.discardChanges();
+    assertNoChanges();
+
+    arr.pop();
+    assertArrayChanges([{
+      index: 2,
+      removed: [3],
+      addedCount: 0
+    }]);
+    observer.close();
+  });
+
+  it('Array', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model[0] = 2;
+
+    assertArrayChanges([{
+      index: 0,
+      removed: [0],
+      addedCount: 1
+    }]);
+
+    model[1] = 3;
+    assertArrayChanges([{
+      index: 1,
+      removed: [1],
+      addedCount: 1
+    }]);
+
+    observer.close();
+  });
+
+  it('Array observe non-array throws', function() {
+    assert.throws(function () {
+      observer = new ArrayObserver({});
+    });
+  });
+
+  it('Array Set Same', function() {
+    var model = [1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model[0] = 1;
+    observer.deliver();
+    assert.isFalse(callbackInvoked);
+    observer.close();
+  });
+
+  it('Array Splice', function() {
+    var model = [0, 1]
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.splice(1, 1, 2, 3); // [0, 2, 3]
+    assertArrayChanges([{
+      index: 1,
+      removed: [1],
+      addedCount: 2
+    }]);
+
+    model.splice(0, 1); // [2, 3]
+    assertArrayChanges([{
+      index: 0,
+      removed: [0],
+      addedCount: 0
+    }]);
+
+    model.splice();
+    assertNoChanges();
+
+    model.splice(0, 0);
+    assertNoChanges();
+
+    model.splice(0, -1);
+    assertNoChanges();
+
+    model.splice(-1, 0, 1.5); // [2, 1.5, 3]
+    assertArrayChanges([{
+      index: 1,
+      removed: [],
+      addedCount: 1
+    }]);
+
+    model.splice(3, 0, 0); // [2, 1.5, 3, 0]
+    assertArrayChanges([{
+      index: 3,
+      removed: [],
+      addedCount: 1
+    }]);
+
+    model.splice(0); // []
+    assertArrayChanges([{
+      index: 0,
+      removed: [2, 1.5, 3, 0],
+      addedCount: 0
+    }]);
+
+    observer.close();
+  });
+
+  it('Array Splice Truncate And Expand With Length', function() {
+    var model = ['a', 'b', 'c', 'd', 'e'];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.length = 2;
+
+    assertArrayChanges([{
+      index: 2,
+      removed: ['c', 'd', 'e'],
+      addedCount: 0
+    }]);
+
+    model.length = 5;
+
+    assertArrayChanges([{
+      index: 2,
+      removed: [],
+      addedCount: 3
+    }]);
+
+    observer.close();
+  });
+
+  it('Array Splice Delete Too Many', function() {
+    var model = ['a', 'b', 'c'];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.splice(2, 3); // ['a', 'b']
+    assertArrayChanges([{
+      index: 2,
+      removed: ['c'],
+      addedCount: 0
+    }]);
+
+    observer.close();
+  });
+
+  it('Array Length', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.length = 5; // [0, 1, , , ,];
+    assertArrayChanges([{
+      index: 2,
+      removed: [],
+      addedCount: 3
+    }]);
+
+    model.length = 1;
+    assertArrayChanges([{
+        index: 1,
+        removed: [1, , , ,],
+        addedCount: 0
+    }]);
+
+    model.length = 1;
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Array Push', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.push(2, 3); // [0, 1, 2, 3]
+    assertArrayChanges([{
+      index: 2,
+      removed: [],
+      addedCount: 2
+    }]);
+
+    model.push();
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Array Pop', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.pop(); // [0]
+    assertArrayChanges([{
+      index: 1,
+      removed: [1],
+      addedCount: 0
+    }]);
+
+    model.pop(); // []
+    assertArrayChanges([{
+      index: 0,
+      removed: [0],
+      addedCount: 0
+    }]);
+
+    model.pop();
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Array Shift', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.shift(); // [1]
+    assertArrayChanges([{
+      index: 0,
+      removed: [0],
+      addedCount: 0
+    }]);
+
+    model.shift(); // []
+    assertArrayChanges([{
+      index: 0,
+      removed: [1],
+      addedCount: 0
+    }]);
+
+    model.shift();
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Array Unshift', function() {
+    var model = [0, 1];
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.unshift(-1); // [-1, 0, 1]
+    assertArrayChanges([{
+      index: 0,
+      removed: [],
+      addedCount: 1
+    }]);
+
+    model.unshift(-3, -2); // []
+    assertArrayChanges([{
+      index: 0,
+      removed: [],
+      addedCount: 2
+    }]);
+
+    model.unshift();
+    assertNoChanges();
+
+    observer.close();
+  });
+
+  it('Array Tracker Contained', function() {
+    arrayMutationTest(
+        ['a', 'b'],
+        [
+          { name: 'splice', args: [1, 1] },
+          { name: 'unshift', args: ['c', 'd', 'e'] },
+          { name: 'splice', args: [1, 2, 'f'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Delete Empty', function() {
+    arrayMutationTest(
+        [],
+        [
+          { name: 'delete', index: 0 },
+          { name: 'splice', args: [0, 0, 'a', 'b', 'c'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Right Non Overlap', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [0, 1, 'e'] },
+          { name: 'splice', args: [2, 1, 'f', 'g'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Left Non Overlap', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [3, 1, 'f', 'g'] },
+          { name: 'splice', args: [0, 1, 'e'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Right Adjacent', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [1, 1, 'e'] },
+          { name: 'splice', args: [2, 1, 'f', 'g'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Left Adjacent', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [2, 2, 'e'] },
+          { name: 'splice', args: [1, 1, 'f', 'g'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Right Overlap', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [1, 1, 'e'] },
+          { name: 'splice', args: [1, 1, 'f', 'g'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Left Overlap', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          // a b [e f g] d
+          { name: 'splice', args: [2, 1, 'e', 'f', 'g'] },
+          // a [h i j] f g d
+          { name: 'splice', args: [1, 2, 'h', 'i', 'j'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Prefix And Suffix One In', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'unshift', args: ['z'] },
+          { name: 'push', arg: ['z'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Shift One', function() {
+    arrayMutationTest(
+        [16, 15, 15],
+        [
+          { name: 'shift', args: ['z'] }
+        ]
+    );
+  });
+
+  it('Array Tracker Update Delete', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'splice', args: [2, 1, 'e', 'f', 'g'] },
+          { name: 'update', index: 0, value: 'h' },
+          { name: 'delete', index: 1 }
+        ]
+    );
+  });
+
+  it('Array Tracker Update After Delete', function() {
+    arrayMutationTest(
+        ['a', 'b', undefined, 'd'],
+        [
+          { name: 'update', index: 2, value: 'e' }
+        ]
+    );
+  });
+
+  it('Array Tracker Delete Mid Array', function() {
+    arrayMutationTest(
+        ['a', 'b', 'c', 'd'],
+        [
+          { name: 'delete', index: 2 }
+        ]
+    );
+  });
+
+  it('Array Random Case 1', function() {
+    var model = ['a','b'];
+    var copy = model.slice();
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.splice(0, 1, 'c', 'd', 'e');
+    model.splice(4,0,'f');
+    model.splice(3,2);
+
+    applySplicesAndAssertDeepEqual(model, copy);
+  });
+
+  it('Array Random Case 2', function() {
+    var model = [3,4];
+    var copy = model.slice();
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.splice(2,0,8);
+    model.splice(0,1,0,5);
+    model.splice(2,2);
+
+    applySplicesAndAssertDeepEqual(model, copy);
+  });
+
+  it('Array Random Case 3', function() {
+    var model = [1,3,6];
+    var copy = model.slice();
+
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+
+    model.splice(1,1);
+    model.splice(0,2,1,7);
+    model.splice(1,0,3,7);
+
+    applySplicesAndAssertDeepEqual(model, copy);
+  });
+
+  function ArrayFuzzer() {}
+
+  ArrayFuzzer.valMax = 16;
+  ArrayFuzzer.arrayLengthMax = 128;
+  ArrayFuzzer.operationCount = 64;
+
+  function randDouble(start, end) {
+    return Math.random()*(end-start) + start;
+  }
+
+  function randInt(start, end) {
+    return Math.round(randDouble(start, end));
+  }
+
+  function randASCIIChar() {
+    return String.fromCharCode(randInt(32, 126));
+  }
+
+  function randValue() {
+    switch(randInt(0, 5)) {
+      case 0:
+        return {};
+      case 1:
+        return undefined;
+      case 2:
+        return null;
+      case 3:
+        return randInt(0, ArrayFuzzer.valMax);
+      case 4:
+        return randDouble(0, ArrayFuzzer.valMax);
+      case 5:
+        return randASCIIChar();
+    }
+  }
+
+  function randArray() {
+    var args = [];
+    var count = randInt(0, ArrayFuzzer.arrayLengthMax);
+    while(count-- > 0)
+      args.push(randValue());
+
+    return args;
+  }
+
+  function randomArrayOperation(arr) {
+    function empty() {
+      return [];
+    }
+
+    var operations = {
+      push: randArray,
+      unshift: randArray,
+      pop: empty,
+      shift: empty,
+      splice: function() {
+        var args = [];
+        args.push(randInt(-arr.length*2, arr.length*2), randInt(0, arr.length*2));
+        args = args.concat(randArray());
+        return args;
+      }
+    };
+
+    // Do a splice once for each of the other operations.
+    var operationList = ['splice', 'update',
+                         'splice', 'delete',
+                         'splice', 'push',
+                         'splice', 'pop',
+                         'splice', 'shift',
+                         'splice', 'unshift'];
+
+    var op = {
+      name: operationList[randInt(0, operationList.length - 1)]
+    };
+
+    switch(op.name) {
+      case 'delete':
+        op.index = randInt(0, arr.length - 1);
+        delete arr[op.index];
+        break;
+
+      case 'update':
+        op.index = randInt(0, arr.length);
+        op.value = randValue();
+        arr[op.index] = op.value;
+        break;
+
+      default:
+        op.args = operations[op.name]();
+        arr[op.name].apply(arr, op.args);
+        break;
+    }
+
+    return op;
+  }
+
+  function randomArrayOperations(arr, count) {
+    var ops = []
+    for (var i = 0; i < count; i++) {
+      ops.push(randomArrayOperation(arr));
+    }
+
+    return ops;
+  }
+
+  ArrayFuzzer.prototype.go = function() {
+    var orig = this.arr = randArray();
+    randomArrayOperations(this.arr, ArrayFuzzer.operationCount);
+    var copy = this.copy = this.arr.slice();
+    this.origCopy = this.copy.slice();
+
+    var observer = new ArrayObserver(this.arr);
+    observer.open(function(splices) {
+      ArrayObserver.applySplices(copy, orig, splices);
+    });
+
+    this.ops = randomArrayOperations(this.arr, ArrayFuzzer.operationCount);
+    observer.deliver();
+    observer.close();
+  }
+
+
+  it('Array Tracker Fuzzer', function() {
+    var testCount = 64;
+
+    for (var i = 0; i < testCount; i++) {
+      var fuzzer = new ArrayFuzzer();
+      fuzzer.go();
+      ensureNonSparse(fuzzer.arr);
+      ensureNonSparse(fuzzer.copy);
+      assert.deepEqual(fuzzer.arr, fuzzer.copy);
+    }
+  });
+
+  it('Array Tracker No Proxies Edits', function() {
+    var model = [];
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+    model.length = 0;
+    model.push(1, 2, 3);
+    assertEditDistance(model, 3);
+    observer.close();
+
+    model = ['x', 'x', 'x', 'x', '1', '2', '3'];
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+    model.length = 0;
+    model.push('1', '2', '3', 'y', 'y', 'y', 'y');
+    assertEditDistance(model, 8);
+    observer.close();
+
+    model = ['1', '2', '3', '4', '5'];
+    observer = new ArrayObserver(model);
+    observer.open(callback);
+    model.length = 0;
+    model.push('a', '2', 'y', 'y', '4', '5', 'z', 'z');
+    assertEditDistance(model, 7);
+    observer.close();
+  });
+});
+</script>