expect
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Package description
The 'expect' npm package is a library for writing test assertions. It is commonly used in conjunction with testing frameworks like Jest or Mocha to validate the behavior of JavaScript code. It provides a range of assertion types and matchers that allow developers to write expressive and readable tests.
Basic Assertions
This feature allows you to assert that a value matches exactly what you expect. The 'toBe' matcher compares with ===.
expect(2 + 2).toBe(4);Object Property Assertions
With this feature, you can assert that an object has a specific property with a certain value. The 'toHaveProperty' matcher checks for the existence and value of a property in an object.
expect({ name: 'Alice', age: 30 }).toHaveProperty('name', 'Alice');Exception Testing
This feature is used to test if a function throws an exception when it is executed. The 'toThrow' matcher is used to assert that an error is thrown with a specific message.
expect(() => { throw new Error('failure'); }).toThrow('failure');Array Containment
This feature allows you to assert that an array contains a specific item. The 'toContain' matcher checks if an array includes the expected item.
expect(['Alice', 'Bob', 'Eve']).toContain('Bob');Asynchronous Assertions
This feature enables you to write assertions for asynchronous code. The 'resolves' matcher waits for a promise to resolve and then checks the resolved value.
expect(Promise.resolve('success')).resolves.toBe('success');Chai is a BDD/TDD assertion library for node and the browser that can be paired with any javascript testing framework. It offers a similar range of matchers and assertions as expect, and it provides a fluent chainable language to construct assertions.
Should.js is an expressive, readable, framework-agnostic assertion library. The key difference is in the style of assertions it offers, using a more fluent chainable API that reads like English.
Assert is a module that provides a set of assertion functions for verifying invariants. It is built into Node.js and is less feature-rich compared to expect, but it serves as a simple way to write assertions in a Node.js environment.
Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It comes with its own assertion library, which provides functionality similar to expect, as expect is actually part of Jest.
Readme
expect is a thin wrapper around node's assert module that lets you write better assertions.
When you use expect, you write assertions similarly to how you would say them, e.g. "I expect this value to be equal to 3" or "I expect this array to contain 3". When you write assertions in this way, you don't need to remember the order of actual and expected arguments to functions like assert.equal, which helps you write better tests.
Asserts that object is strictly equal to value using assert.strictEqual.
Asserts that object is not strictly equal to value using assert.notStrictEqual.
Asserts that the given object equals value using assert.equal.
Asserts that the given object is not equal to value using assert.notEqual.
Asserts that the given block throws an error using assert.throws. The error argument may be a constructor, RegExp, or validation function.
expect(function () {
throw new Error('boom!');
}).toThrow(/boom/);
Asserts that the given block does not throw using assert.doesNotThrow.
Asserts the given object is an instanceof constructor.
expect(new User).toBeA(User);
Asserts the given string matches pattern, which must be a RegExp.
expect('a string').toMatch(/string/);
Asserts the given number is less than value.
expect(2).toBeLessThan(3);
Asserts the given number is greater than value.
expect(3).toBeGreaterThan(2);
Asserts the given array contains value. The comparator function, if given, should compare two objects and either return false or throw if they are not equal. It defaults to assert.deepEqual.
expect([ 1, 2, 3 ]).toInclude(3);
Asserts the given array does not contain value. The comparator function, if given, should compare two objects and either return false or throw if they are not equal. It defaults to assert.deepEqual.
expect([ 1, 2, 3 ]).toExclude(4);
Using npm:
$ npm install expect
Please file issues on the issue tracker on GitHub.
To run the tests in node:
$ npm install
$ npm test
FAQs
This package exports the `expect` function used in [Jest](https://jestjs.io/). You can find its documentation [on Jest's website](https://jestjs.io/docs/expect).
The npm package expect receives a total of 27,660,403 weekly downloads. As such, expect popularity was classified as popular.
We found that expect demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 2 open source maintainers collaborating on the project.
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