> For the complete documentation index, see [llms.txt](https://mistborn.gitbook.io/til-coding/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mistborn.gitbook.io/til-coding/javascript/automated-testing-with-mocha.md).
# Automated testing with mocha
## Why we need tests?
當撰寫一個函式，我們會預期產出的結果，我們可能會帶入不同參數用 `console` 來檢視結果，但若有錯誤修改後，又要一一測試之前帶入的參數，所以測試跟開發是分開的，測試可以很容易執行，檢查主要使用沒問題。
## Behavior Driven Development (BDD)
行為驅動的開發被用在許多專案中，BDD 包含 3 件事測試、文件、範例。
## Development of “pow”: the spec
我們要寫一個函式，pow(x, n) 該函式將產出 x 的 n 次方，在創建函式之前可以描述該函式的功能有 3 個規範。
1. `describe("title", function() { ... })` 描述函式名稱。
2. `it("title", function() { ... })` 描述函式功能
3. `assert.equal(value1, value2)` 帶入參數測試函數的產出是否正確
## The development flow
1. 撰寫規範
2. 撰寫基本函式可以跑測試
3. 執行測試框架 mocha ，檢測函示是否正確
4. 增加更多案例到測試中
5. 測試失敗修改函式
6. 重複 3 \~ 5 步驟
## The spec in action
測試主要用到 3 個 librarues。
* mocha 主要執行的框架 包含 `descibe` `it` 等函數。
* chai 有很多 assertions 函式，範例使用 `assert.equal`。
* Sinon 用來監視函數模擬內建函式。
```javascript
```
頁面分為 5 個部分
1. head 引入 libraries
2. script 撰寫測試的函示
3. 測試程式碼寫在 test.js
4. `
` 用來輸出 mocha 執行的結果
5. `mocha.run()` 執行 mocha
## Improving the spec
增加更多情況到測試中，一個測試只檢查一個功能。
```javascript
// method1
describe("pow", function() {
it("raises to n-th power", function() {
assert.equal(pow(2, 3), 8);
assert.equal(pow(3, 4), 81);
});
});
// method2 better
describe("pow", function() {
it("2 raised to power 3 is 8", function() {
assert.equal(pow(2, 3), 8);
});
it("3 raised to power 3 is 27", function() {
assert.equal(pow(3, 3), 27);
});
});
```
## Improving the implementation
```javascript
function pow(x, n) {
let result = 1;
for (let i = 0; i < n; i++) {
result *= x;
}
return result;
}
// test
describe("pow", function() {
function makeTest(x) {
let expected = x * x * x;
it(`${x} in the power 3 is ${expected}`, function() {
assert.equal(pow(x, 3), expected);
});
}
for (let x = 1; x <= 5; x++) {
makeTest(x);
}
});
```
## Nested describe
`makeTest()` 只用在 for 迴圈內，因此將他們綁在一起，下一個測試不會在用到。
```javascript
describe("pow", function() {
describe("raises x to power 3", function() {
function makeTest(x) {
let expected = x * x * x;
it(`${x} in the power 3 is ${expected}`, function() {
assert.equal(pow(x, 3), expected);
});
}
for (let x = 1; x <= 5; x++) {
makeTest(x);
}
});
// ... more tests to follow here, both describe and it can be added
});
```
```javascript
describe("test", function() {
before(() => alert("Testing started – before all tests"));
after(() => alert("Testing finished – after all tests"));
beforeEach(() => alert("Before a test – enter a test"));
afterEach(() => alert("After a test – exit a test"));
it('test 1', () => alert(1));
it('test 2', () => alert(2));
});
// result
Testing started – before all tests (before)
Before a test – enter a test (beforeEach)
1
After a test – exit a test (afterEach)
Before a test – enter a test (beforeEach)
2
After a test – exit a test (afterEach)
Testing finished – after all tests (after)
```
## Extending the spec
增加規範，程式碼出現錯誤，修改程式碼。
```javascript
// add spec
describe("pow", function() {
// ...
it("for negative n the result is NaN", function() {
assert.isNaN(pow(2, -1));
});
it("for non-integer n the result is NaN", function() {
assert.isNaN(pow(2, 1.5));
});
});
// improve pow(x ,n)
function pow(x, n) {
if (n < 0) return NaN;
if (Math.round(n) != n) return NaN;
let result = 1;
for (let i = 0; i < n; i++) {
result *= x;
}
return result;
}
```
* `assert.equal(value1, value2)` – checks the equality `value1 == value2`.
* `assert.strictEqual(value1, value2)` – checks the strict equality `value1 === value2`.
* `assert.notEqual`, `assert.notStrictEqual` – inverse checks to the ones above.
* `assert.isTrue(value)` – checks that `value === true`
* `assert.isFalse(value)` – checks that `value === false`
* …the full list is in the [docs](http://chaijs.com/api/assert/)