五、断言与匹配器
5.1 常用断言方法
- toBe：判断两个值是否严格相等（使用===）。
test('two plus two is four', () => {
expect(2 + 2).toBe(4);
});test('two plus two is four', () => {
expect(2 + 2).toBe(4);
});- toEqual：用于比较对象或数组的内容是否相等。
test('objects are equal', () => {
const obj1 = { a: 1 };
const obj2 = { a: 1 };
expect(obj1).toEqual(obj2);
});test('objects are equal', () => {
const obj1 = { a: 1 };
const obj2 = { a: 1 };
expect(obj1).toEqual(obj2);
});- toBeTruthy：判断值是否为真。
test('true is truthy', () => {
expect(true).toBeTruthy();
});test('true is truthy', () => {
expect(true).toBeTruthy();
});- toBeFalsy：判断值是否为假。
test('false is falsy', () => {
expect(false).toBeFalsy();
});test('false is falsy', () => {
expect(false).toBeFalsy();
});- toBeGreaterThan：判断值是否大于某个值。
test('5 is greater than 3', () => {
expect(5).toBeGreaterThan(3);
});test('5 is greater than 3', () => {
expect(5).toBeGreaterThan(3);
});- toBeLessThan：判断值是否小于某个值。
test('3 is less than 5', () => {
expect(3).toBeLessThan(5);
});test('3 is less than 5', () => {
expect(3).toBeLessThan(5);
});5.2 高级断言技巧
- 嵌套断言：可以在一个断言中嵌套多个断言，以更细粒度地验证复杂数据结构。
test('nested objects are equal', () => {
const obj1 = { a: { b: 1 } };
const obj2 = { a: { b: 1 } };
expect(obj1).toEqual({
a: expect.objectContaining({
b: expect.any(Number)
})
});
});test('nested objects are equal', () => {
const obj1 = { a: { b: 1 } };
const obj2 = { a: { b: 1 } };
expect(obj1).toEqual({
a: expect.objectContaining({
b: expect.any(Number)
})
});
});- 自定义匹配器：Jest 允许开发者自定义匹配器，以满足特定的测试需求。
expect.extend({
toBeEven: (received) => {
const pass = received % 2 === 0;
if (pass) {
return {
message: () => `expected ${received} not to be even`,
pass: true
};
} else {
return {
message: () => `expected ${received} to be even`,
pass: false
};
}
}
});
test('2 is even', () => {
expect(2).toBeEven();
});expect.extend({
toBeEven: (received) => {
const pass = received % 2 === 0;
if (pass) {
return {
message: () => `expected ${received} not to be even`,
pass: true
};
} else {
return {
message: () => `expected ${received} to be even`,
pass: false
};
}
}
});
test('2 is even', () => {
expect(2).toBeEven();
});