test(heap): add tests for is empty methods

tests/methods.spec.ts

@@ -0,0 +1,16 @@
+/* eslint-disable no-constant-condition */
+/* eslint-disable no-cond-assign */
+import { expect } from 'chai';
+import { MaxHeap } from '../src/index';
+
+describe('Methods', () => {
+  it('the isEmpty method works', () => {
+    const maxHeap = new MaxHeap((x) => x);
+    maxHeap.insertMany([1].values());
+
+    expect(maxHeap.isEmpty()).to.eq(false);
+
+    maxHeap.pop();
+    expect(maxHeap.isEmpty()).to.eq(true);
+  });
+});