Add support for assert.sizeOf (relates to #6)

README.md

@@ -94,3 +94,15 @@ var a = List.of(1, 2, 3);
 var b = List.of(1, 2, 3);
 assert.equal(a, b);
 ```
+
+### .sizeOf(collection, length)
+
+- **@param** *{Collection}* collection
+- **@param** *{Number}* size
+
+Asserts that the immutable collection has the expected size.
+
+```js
+assert.sizeOf(List.of(1, 2, 3), 3);
+assert.sizeOf(new List(), 0);
+```

chai-immutable.js

@@ -287,4 +287,24 @@ module.exports = function (chai, utils) {
     }
     else return assert.equal;
   };
+
+  /**
+   * ### .sizeOf(collection, length)
+   *
+   * Asserts that the immutable collection has the expected size.
+   *
+   * ```js
+   * assert.sizeOf(List.of(1, 2, 3), 3);
+   * assert.sizeOf(new List(), 0);
+   * ```
+   *
+   * @name sizeOf
+   * @param {Collection} collection
+   * @param {Number} size
+   * @api public
+   */
+
+  assert.sizeOf = function (collection, expected) {
+    new Assertion(collection).size(expected);
+  };
 };

test/test.js

@@ -193,5 +193,15 @@ describe('chai-immutable', function () {
         assert.notDeepEqual(list3, new List());
       });
     });
+
+    describe('sizeOf assertion', function () {
+      it('should be true when given the right size', function () {
+        assert.sizeOf(List.of(1, 2, 3), 3);
+      });
+
+      it('should work with empty collections', function () {
+        assert.sizeOf(new List(), 0);
+      });
+    });
   });
 });