javascript - 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 ComparisonFunction 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“name”属性对“arrayOfObjects”进行排序。 方法工作正常，问题是: 我如何比较具有不同参数的函数调用

  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());
  });

这就是我现在拥有的，但它不起作用。运行代码后收到的错误是:

 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

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
}

仅对代码进行非功能性更改会破坏测试。

更糟糕的是，如果代码有功能更改，则测试无法保证新实现的行为与旧实现类似，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，您想要执行的操作是测试代码的行为并在那里设定您的期望。这样，如果实现发生变化，您可以确保实现仍然符契约(Contract)一组期望。

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。在伪代码中，它看起来有点像这样:

//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);

如果您愿意，您还可以在更细粒度的级别添加更多测试，以进一步约束期望。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)

或者不区分大小写:

//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 future 的更改将准确满足您的需求。