@std/expect

Overview Jump to heading#

This module provides Jest compatible expect assertion functionality.

import { expect } from "@std/expect";

const x = 6 * 7;
expect(x).toEqual(42);
expect(x).not.toEqual(0);

await expect(Promise.resolve(x)).resolves.toEqual(42);

Currently this module supports the following functions:

• Common matchers:
  • toBe
  • toEqual
  • toStrictEqual
  • toMatch
  • toMatchObject
  • toBeDefined
  • toBeUndefined
  • toBeNull
  • toBeNaN
  • toBeTruthy
  • toBeFalsy
  • toContain
  • toContainEqual
  • toHaveLength
  • toBeGreaterThan
  • toBeGreaterThanOrEqual
  • toBeLessThan
  • toBeLessThanOrEqual
  • toBeCloseTo
  • toBeInstanceOf
  • toThrow
  • toHaveProperty
• Mock related matchers:
  • toHaveBeenCalled
  • toHaveBeenCalledTimes
  • toHaveBeenCalledWith
  • toHaveBeenLastCalledWith
  • toHaveBeenNthCalledWith
  • toHaveReturned
  • toHaveReturnedTimes
  • toHaveReturnedWith
  • toHaveLastReturnedWith
  • toHaveNthReturnedWith
• Asymmetric matchers:
  • expect.anything
  • expect.any
  • expect.arrayContaining
  • expect.not.arrayContaining
  • expect.objectContaining
  • expect.not.objectContaining
  • expect.closeTo
  • expect.stringContaining
  • expect.not.stringContaining
  • expect.stringMatching
  • expect.not.stringMatching
• Utilities:
  • expect.addSnapshotSerializer
  • expect.assertions
  • expect.addEqualityTester
  • expect.extend
  • expect.hasAssertions

Only these functions are still not available:

• Matchers:
  • toMatchSnapshot
  • toMatchInlineSnapshot
  • toThrowErrorMatchingSnapshot
  • toThrowErrorMatchingInlineSnapshot

The tracking issue to add support for unsupported parts of the API is https://github.com/denoland/std/issues/3964.

This module is largely inspired by x/expect module by Allain Lalonde.

Add to your project Jump to heading#

deno add jsr:@std/expect

See all symbols in @std/expect on

什么是 expect？ Jump to heading#

一个兼容 Jest 的流式断言 API。与独立的断言函数不同， 您可以编写像 expect(value).toBe(1) 这样的预期，并能链式调用修饰符，如 .not、.resolves 和 .rejects。

何时使用 @std/expect Jump to heading#

如果您喜欢类似 Jest 的 API，具有流畅、易读的断言和丰富的匹配器， 尤其是在从 Jest 迁移时。

示例 Jump to heading#

import { expect } from "@std/expect";

expect({ a: 1, b: 2 }).toMatchObject({ a: 1 });
await expect(Promise.resolve(42)).resolves.toBe(42);
expect([1, 2, 3]).toContain(2);

// 抛出异常和异步拒绝
expect(() => JSON.parse("{"))
  .toThrow(SyntaxError);
await expect(Promise.reject(new Error("boom")))
  .rejects.toThrow("boom");

// 浮点近似，正则匹配
expect(0.1 + 0.2).toBeCloseTo(0.3, 15);
expect("hello world").toMatch(/world/);

// 使用非对称匹配器
expect({ id: 1, name: "Ada" })
  .toEqual(expect.objectContaining({ name: expect.stringMatching(/^A/) }));

与 Deno.test 一起使用 Jump to heading#

import { expect } from "@std/expect";
Deno.test("基本 expect 测试", () => {
  const value = 2 + 2;
  expect(value).toBe(4);
});

更多关于 Deno 中测试的信息，请参见 测试文档。

小贴士 Jump to heading#

• 使用 toEqual 进行深度数据比较，使用 toBe 进行身份比较。
• 优先使用 .resolves / .rejects 来处理 Promise。
• 优先使用 .resolves / .rejects 来处理 Promise。
• 使用 toStrictEqual 进行更严格的深度检查（无额外属性等）。
• 需要时通过 expect.extend 扩展自定义匹配器。