Jest 断言与匹配器（Expect）

推荐文档：https://blog.csdn.net/biraotian/article/details/111329794

常用匹配器

/* expect断言测试 */
const errorFn = () => {
	throw new Error("错误信息！！");
};
describe("Expect断言测试", () => {
	/* 常用 */
	it("toBe()：全等判断", () => {
		expect(1).toBe(1);
	});
	it("not toBe：不等于", () => {
		expect(2).not.toBe(1);
	});
	it("toEqual：匹配对象是否相等", () => {
		expect({ username: "sunshine" }).toEqual({ username: "sunshine" });
	});
	it("toBeNull：匹配值是否为null", () => {
		expect(null).toBeNull();
	});
	it("toBeUndefined：匹配是否为undefined", () => {
		expect(undefined).toBeUndefined();
	});
	it("toBeTruthy：匹配某个值等于true", () => {
		expect(true).toBeTruthy();
	});
	it("toBeFalsy：匹配某个值为假", () => {
		expect(false).toBeFalsy();
	});
	/* 数字相关对比 */
	it("toBeGreaterThan：比某个数字大", () => {
		expect(1).toBeGreaterThan(0);
	});
	it("toBeLessThan：比某个数字小", () => {
		expect(2).toBeLessThan(3);
	});
	it("toBeGreaterThanOrEqual：大于或等于某个数字", () => {
		expect(2).toBeGreaterThanOrEqual(2);
	});
	it("toBeLessThanOrEqual：小于或等于某个数字", () => {
		expect(1).toBeLessThanOrEqual(1);
	});
	it("toBeCloseTo：计算浮点数字相加是否相等", () => {
		// expect(0.1 + 0.2).toBe(0.3); // js中0.1 + 0.2 = 0.30000000000000004
		expect(0.1 + 0.2).toBeCloseTo(0.3);
	});
	/* 字符串相关 */
	it("toMatch：字符串内是否包含某个字符串", () => {
		expect("hello").toMatch("hel");
	});
	/* 数组相关 */
	it("toContain：是否包含该元素", () => {
		expect([1, 2, 3, 4]).toContain(3);
		expect(new Set([1, 2, 3, 4])).toContain(3);
	});
	/* 异常相关 */
	it("抛出错误", () => {
		expect(errorFn).toThrow();
	});
});

补充匹配器

describe("补充匹配器", () => {
	it("toMatch：正则匹配字符串", () => {
		expect("hello world").toMatch(/world$/);
	});
	it("toHaveLength：断言数组/字符串长度", () => {
		expect([1, 2, 3]).toHaveLength(3);
		expect("abc").toHaveLength(3);
	});
	it("toThrow：断言错误信息内容", () => {
		const fn = () => {
			throw new Error("参数错误");
		};
		expect(fn).toThrow("参数错误");
	});
	it("toContainEqual：断言对象数组中是否包含某个对象", () => {
		expect([{ id: 1 }, { id: 2 }]).toContainEqual({ id: 2 });
	});
	it("toMatchSnapshot：快照匹配，结构不变即通过", () => {
		const user = { name: "sunshine", role: "admin" };
		expect(user).toMatchSnapshot();
	});
});

异步代码断言

// 方法一：回调函数，手动调用 done 表示测试结束，注意调用 done(error) 处理异常分支
it("回调式异步", done => {
	fetchData((err, data) => {
		if (err) return done(err);
		expect(data).toBe("ok");
		done();
	});
});

// 方法二：返回 Promise
it("Promise式异步", () => {
	return fetchData().then(data => {
		expect(data).toBe("ok");
	});
});

// 方法三：async/await（推荐）
it("async/await式异步", async () => {
	const data = await fetchData();
	expect(data).toBe("ok");
});

// 方法四：resolves / rejects 匹配器
it("resolves匹配器", async () => {
	await expect(fetchData()).resolves.toBe("ok");
});
it("rejects匹配器", async () => {
	await expect(fetchError()).rejects.toThrow("失败");
});