Implement DomElementObjectPool with tests

src/utils/DomElementObjectPool.test.ts

@@ -0,0 +1,47 @@
+import { assert } from 'chai';
+import { DomElementObjectPool } from './DomElementObjectPool';
+
+class MockDocument {
+  private _attr: {[key: string]: string} = {};
+  constructor() {}
+  public getAttribute(key: string): string { return this._attr[key]; };
+  public setAttribute(key: string, value: string): void { this._attr[key] = value; }
+}
+
+describe('DomElementObjectPool', () => {
+  let pool: DomElementObjectPool;
+
+  beforeEach(() => {
+    pool = new DomElementObjectPool('span');
+    (<any>global).document = {
+      createElement: () => new MockDocument()
+    };
+  });
+
+  it('should acquire distinct elements', () => {
+    const element1 = pool.acquire();
+    const element2 = pool.acquire();
+    assert.notEqual(element1, element2);
+  });
+
+  it('should acquire released elements', () => {
+    const element = pool.acquire();
+    pool.release(element);
+    assert.equal(pool.acquire(), element);
+  });
+
+  it('should handle a series of acquisitions and releases', () => {
+    const element1 = pool.acquire();
+    const element2 = pool.acquire();
+    pool.release(element1);
+    assert.equal(pool.acquire(), element1);
+    pool.release(element1);
+    pool.release(element2);
+    assert.equal(pool.acquire(), element2);
+    assert.equal(pool.acquire(), element1);
+  });
+
+  it('should throw when releasing an element that was not acquired', () => {
+    assert.throws(() => pool.release(document.createElement('span')));
+  });
+});