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expect

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).


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Package description

What is expect?

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.

What are expect's main functionalities?

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');

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expect

This package exports the expect function used in Jest. You can find its documentation on Jest's website.

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Package last updated on 12 May 2024

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