基本但正确使用 beforeEach() 或 afterEach() 与 mocha.js 和 chai.js

Question

我想使用 mocha/chai 来测试与二叉搜索树相关的代码。在这里，我正在测试公共insert方法。我想在每个语句之前使用beforeEach()和/或afterEach()钩子重置测试环境it()，这样我就不必完全重复基础知识。但是，我不断收到各种错误。

规格

describe("BinarySearchTree insert function", function() {

  beforeEach(function() {
    var binarySearchTree = new BinarySearchTree();
    binarySearchTree.insert(5);
  });

  it("creates a root node with value equal to the first inserted value", function () {
    expect(binarySearchTree.root.value).to.equal(5);
  });

  it("has a size equal to the amount of inserted values", function () {
    binarySearchTree.insert(3);
    expect(binarySearchTree.size).to.equal(2);
  });

  it("returns an error for non-unique values", function () {
    binarySearchTree.insert(3);
    expect(binarySearchTree.insert(3)).to.throw(String);
  });

  it("if inserted value is larger than current node, make or descend to rightChild", function () {
    binarySearchTree.insert(3);
    binarySearchTree.insert(10);
    binarySearchTree.insert(7);
    expect(binarySearchTree.root.rightChild.value).to.equal(10);
  });

});

错误：ReferenceError: binarySearchTree is not defined

事实上，我在没有afterEach()重置测试环境之前就预料到会出现错误，而不是因为binarySearchTree没有定义。如果可能的话，我想只用 Mocha 和 Chai 来完成这个任务（而不是像 Sinon 等其他包）。

测试代码

exports.Node = Node;

function Node(value) {
  this.value = value;
  this.leftChild = null;
  this.rightChild = null;
}

exports.BinarySearchTree = BinarySearchTree;

function BinarySearchTree() {
  this.root = null;
  this.size = 0;
}

BinarySearchTree.prototype.insert = function(value) {
  // 1) when root node is already instantiated
  if (this.root === null) {
    // tree is empty
    this.root = new Node(value);
    this.size++;
  } else {
  // 2) nodes are already inserted
    var findAndInsert = function (currentNode) {
      if (value === currentNode.value) {
        throw new Error('must be a unique value');
      }
      // base case
      if (value > currentNode.value) {
        // belongs in rightChild
        if (currentNode.rightChild === null) {
          currentNode.rightChild = new Node(value);
        } else {
          findAndInsert(currentNode.rightChild);
        }
      } else if (value < currentNode.value) {
        // belongs in leftChild
        if (currentNode.leftChild === null) {
          currentNode.leftChild = new Node(value);
        } else {
          findAndInsert(currentNode.leftChild);
        }
      }
    };
    findAndInsert(this.root);
    this.size++;
  }
};

额外问题...我不确定我是否正确测试了抛出的错误（当插入非唯一值时）？

Answer 1

它是未定义的，因为它不在测试函数范围内。在描述范围中提前一步定义它。作为参考，请查看 Angular 文档。https://docs.angularjs.org/guide/unit-testing

describe("BinarySearchTree insert function", function() {
  var binarySearchTree;
  beforeEach(function() {
    binarySearchTree = new BinarySearchTree();
    binarySearchTree.insert(5);
  });

  it("creates a root node with value equal to the first inserted value", function () {
    expect(binarySearchTree.root.value).to.equal(5);
  });

  it("has a size equal to the amount of inserted values", function () {
    binarySearchTree.insert(3);
    expect(binarySearchTree.size).to.equal(2);
  });

  it("returns an error for non-unique values", function () {
    binarySearchTree.insert(3);
    expect(binarySearchTree.insert(3)).to.throw(String);
  });

  it("if inserted value is larger than current node, make or descend to rightChild", function () {
    binarySearchTree.insert(3);
    binarySearchTree.insert(10);
    binarySearchTree.insert(7);
    expect(binarySearchTree.root.rightChild.value).to.equal(10);
  });

});