多次设置
beforeEach 和 afterEach
示例：
beforeEach(() => {
initializeCityDatabase();
});
afterEach(() => {
clearCityDatabase();
});
test('city database has Vienna', () => {
expect(isCity('Vienna')).toBeTruthy();
});
test('city database has San Juan', () => {
expect(isCity('San Juan')).toBeTruthy();
});
如果设置中是异步代码，那么可以使用 done 参数或返回 promise。
示例：
beforeEach(() => {
return initializeCityDatabase();
});
一次性设置
beforeAll 和 afterAll
示例：
beforeAll(() => {
return initializeCityDatabase();
});
afterAll(() => {
return clearCityDatabase();
});
test('city database has Vienna', () => {
expect(isCity('Vienna')).toBeTruthy();
});
test('city database has San Juan', () => {
expect(isCity('San Juan')).toBeTruthy();
});
作用域
默认情况下，before 和 after 的块可以应用到文件中的每个测试。 此外可以通过 describe 块来将测试分组。 当 before 和 after 的块在 describe 块内部时，则其只适用于该 describe 块内的测试。
// 应用到此文件中的所有测试上
beforeEach(() => {
return initializeCityDatabase();
});
test('city database has Vienna', () => {
expect(isCity('Vienna')).toBeTruthy();
});
test('city database has San Juan', () => {
expect(isCity('San Juan')).toBeTruthy();
});
describe('matching cities to foods', () => {
// 仅应用到当前 describe 块中的测试
beforeEach(() => {
return initializeFoodDatabase();
});
test('Vienna <3 sausage', () => {
expect(isValidCityFoodPair('Vienna', 'Wiener Schnitzel')).toBe(true);
});
test('San Juan <3 plantains', () => {
expect(isValidCityFoodPair('San Juan', 'Mofongo')).toBe(true);
});
});
注意，顶级的 beforeEach 会在内部 describe 块中的 beforeEach 之前执行。
beforeAll(() => console.log('1 - beforeAll'));
afterAll(() => console.log('1 - afterAll'));
beforeEach(() => console.log('1 - beforeEach'));
afterEach(() => console.log('1 - afterEach'));
test('', () => console.log('1 - test'));
describe('Scoped / Nested block', () => {
beforeAll(() => console.log('2 - beforeAll'));
afterAll(() => console.log('2 - afterAll'));
beforeEach(() => console.log('2 - beforeEach'));
afterEach(() => console.log('2 - afterEach'));
test('', () => console.log('2 - test'));
});
// 1 - beforeAll
// 1 - beforeEach
// 1 - test
// 1 - afterEach
// 2 - beforeAll
// 1 - beforeEach
// 2 - beforeEach
// 2 - test
// 2 - afterEach
// 1 - afterEach
// 2 - afterAll
// 1 - afterAll
describe 和 test 块执行顺序
Jest 会在执行具体的 test 块之前执行所有的 describe 处理器部分。这也是为什么在 before* 和 after* 中做前后期准备，而不是在 describe 中的原因。一旦 describe 部分完成执行，随机顺序执行所有的测试。
describe('outer', () => {
console.log('describe outer-a');
describe('describe inner 1', () => {
console.log('describe inner 1');
test('test 1', () => {
console.log('test for describe inner 1');
expect(true).toEqual(true);
});
});
console.log('describe outer-b');
test('test 1', () => {
console.log('test for describe outer');
expect(true).toEqual(true);
});
describe('describe inner 2', () => {
console.log('describe inner 2');
test('test for describe inner 2', () => {
console.log('test for describe inner 2');
expect(false).toEqual(false);
});
});
console.log('describe outer-c');
});
// describe outer-a
// describe inner 1
// describe outer-b
// describe inner 2
// describe outer-c
// test for describe inner 1
// test for describe outer
// test for describe inner 2
