Fix test regression from PR 3289

test/unit/attributes.html

@@ -283,7 +283,11 @@
     // applied to property with effect
     assert.strictEqual(compose.$.basic.prop, 'compose');
     assert.equal(compose.$.basic.propChangedCount, 1);
-    assert.equal(compose.$.basic.attr1ChangedCount, 1);
+    // Note: Attribute binding does not participate in efficient configuration
+    // per #3288.  As such, a property bound with an attribute binding will
+    // see its default value first, then be overwritten when the attribute
+    // binding runs and re-deserializes to the property, hence 2 observer calls
+    assert.equal(compose.$.basic.attr1ChangedCount, 2);
     assert.equal(compose.prop2, 'hi');
   });