如何在javascript中测试两个具有不同参数值的返回函数？

Question

我有一个返回比较函数的函数

  getComparisonFunction(propertyOfComparison) {
    const func = function(a, b){
      if ( a[propertyOfComparison] < b[propertyOfComparison] ) {
        return -1;
      }
      if ( a[propertyOfComparison] > b[propertyOfComparison] ) {
        return 1;
      }
      return 0;
    };

    return func;
  }

此方法将在javascript“排序”方法中使用。 例如：

arrayOfObjects.sort(getComparisonFunction('name'));

此方法将按“名称”属性对“arrayOfObjects”进行排序。 方法工作正常，问题是： 我如何将函数调用与不同的参数进行比较

  it('should get correct comparison function', function () {
    const func = component.getComparisonFunction('testProperty');

    const expectedFunc = function(a, b){
      if ( a['testProperty'] < b['testProperty'] ) {
        return -1;
      }
      if ( a['testProperty'] > b['testProperty'] ) {
        return 1;
      }
      return 0;
    };

    expect(func.toString()).toEqual(expectedFunc.toString());
  });

这是我现在拥有的，但它不起作用。运行代码后我收到的错误是：

 Expected 'function (a, b) {
                if (a[propertyOfComparison] < b[propertyOfComparison]) {
                    return -1;
                }
                if (a[propertyOfComparison] > b[propertyOfComparison]) {
                    return 1;
                }
                return 0;
            }' to equal 'function (a, b) {
                if (a['testProperty'] < b['testProperty']) {
                    return -1;
                }
                if (a['testProperty'] > b['testProperty']) {
                    return 1;
                }
                return 0;
            }'.

Answer 1

如果您想通过提供的任何参数实现排序，您可以尝试以下操作：

const array=[
  {name:'C',Key:'14',val:3},
  {name:'B',Key:'12',val:2},
  {name:'A',Key:'11',val:1},
  {name:'D',Key:'16',val:4},
  {name:'E',Key:'18',val:5}
];

console.log(array);

function comparer(prop){
  return function(a,b){
    return a[prop]-b[prop];
  }
};
array.sort(comparer('Key'));
console.log(array);
array.sort(comparer('val'));
console.log(array);

此外，要对其进行测试，只需使用上述测试用例并检查其是否按照您的实现进行排序。

Answer 2

检查函数的代码作为测试非常很脆弱，很容易破坏给你一个假阴性：

let someFn = function(a, b) {
  return a + b;
}

let expected = `function(a, b) {
  return a + b;
}`

console.log("Test original implementation:", test(someFn.toString(), expected));

//later the code style is changed to remove extra whitespace and make it one line
someFn = function(a, b) { return a+b; }

console.log("Test updated implementation:", test(someFn.toString(), expected));

//simple testing
function test(expected, actual) {
  return expected == actual
}

只是对代码进行非功能性更改会破坏测试。

更糟糕的是，如果对代码进行 功能更改，则测试无法保证新实现的行为与旧实现一样，因为它只查看代码的结构：

//simplified case of what the actual code could be doing
function someCodeBaseFunction() {
  let someInput = [8, 12, 42];
  return someFn(...someInput)
}

let someFn = function(a, b) { return a+b; }

let expected = `function(a, b) { return a+b; }`

console.log("Test original implementation:", test(someFn.toString(), expected));

console.log("Codebase usage:", someCodeBaseFunction()); //20, as the third number is ignored

//new implementation
someFn = function(...args) { 
  return args.reduce((a, b) => a + b); 
}

//update the test, so it passes
expected = `function(...args) { 
  return args.reduce((a, b) => a + b); 
}`

console.log("Test updated implementation:", test(someFn.toString(), expected));

//some existing line of code
console.log("Codebase usage:", someCodeBaseFunction()); //62, as the third number is now used

//simple testing
function test(expected, actual) {
  return expected == actual
};

相反，您要测试代码的行为，并在那里设定您的期望。这样，如果实施发生变化，您可以确保实施仍然符合相同的预期。

在这种情况下，您需要创建一个最初无序的示例输入，尝试对其进行排序，然后期望该顺序按您的预期工作。在看起来有点像这样的伪代码中：

//arrange
input = [
 {testProperty: "c", id: 1},
 {testProperty: "a", id: 2},
 {testProperty: "d", id: 3},
 {testProperty: "b", id: 4}
];

expected = [
 {testProperty: "a", id: 2},
 {testProperty: "b", id: 4},
 {testProperty: "c", id: 1},
 {testProperty: "d", id: 3}
];

//act
input.sort(component.getComparisonFunction('testProperty'))

//assert
expect(input).toEqual(expected);

如果需要，您还可以添加更多更细粒度的测试，以进一步绑定期望。例如，如果您想确保比较区分大小写

//arrange
a = { testProperty: "a" };
b = { testProperty: "B" };

//act
result = component.getComparisonFunction('testProperty')(a, b)

//assert
expect(result).toBeGreaterThanOrEqual(1)

或不区分大小写：

//arrange
a = { testProperty: "a" };
b = { testProperty: "B" };

//act
result = component.getComparisonFunction('testProperty')(a, b)

//assert
expect(result).toBeLessThanOrEqual(-1)

这更清楚地定义了您的期望，并确保未来的更改将完全满足您的需求。