Mocking

As explained in Functional Programming in JavaScript

A testing technique that replaces external dependencies with controlled stand-ins whose behavior and interactions can be asserted.

How Functional Programming in JavaScript covers it

How deep it goes

Demonstrates mock setup, expectations, verification, and restoration, but does not detail mock implementation internals.

Examples

Uses a mocked student database to test findStudent within the showStudent program.

What it assumes

Builds from testing pure functions toward testing functions that depend on impure IO.

What you can do after

Apply it via QUnit and Sinon.JS to simulate database responses and verify dependency interactions.

How it connects

Connects mocking with external dependencies, side effects, pure functions, QUnit, and Sinon.JS.

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Also explained in

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  Unit Testing Principles, Practices, and PatternsMocking is the practice of creating, configuring, or applying mocks in software tests.
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  The Art of Unit Testing 3eA programmable test double that replaces an outgoing dependency and records or verifies interactions with it.
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  Practical Automation with PowerShell: Effective scripting from the console to the cloudA mock is a test double that simulates a dependency or interaction so that code can be tested under controlled conditions.
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  Build AI-Enhanced Web AppsMocking is the replacement of a real dependency or external response with a controlled test double.
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  Build Python Web Apps with StreamlitMocking is the process of replacing real dependencies with fake, controlled versions during testing.
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  Modern AngularA mock implementation is a test-specific substitute implementation that simulates the behavior of a dependency.
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  Functional Design and Architecture: Examples in HaskellA mock is a configurable test-double implementation that simulates a real component or service without invoking the real one.
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  Shipping Go: Develop, deliver, discuss, design, and go againA mock is a programmable test double that records or verifies interactions and can return controlled results or errors.
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  Build Financial Software with Generative AI (From Scratch)Mocking is a testing and development technique that replaces real data or dependencies with controlled predefined substitutes.
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  Kafka Streams in Action, Second EditionA mock object is a test double that implements a collaborator's interface while providing explicitly configured behavior instead of performing the collaborator's real operations.
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  Bootstrapping Microservices, Second Edition: With Docker, Kubernetes, GitHub Actions, and TerraformMocking is the replacement of a software dependency with a controlled substitute that provides compatible behavior for development or testing.
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  Quarkus in ActionMocking is the practice of substituting controlled test doubles for components that are unsuitable or undesirable to run during a test.
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  Data Pipelines with Apache Airflow, Second EditionA mock is a test double that replaces a dependency with controlled behavior for verifying software interactions.
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  Learn Go with Pocket-Sized ProjectsA mock is a test double that imitates a component's interface while allowing interactions or outputs to be controlled and inspected.
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  React in DepthMocking is a testing technique that replaces a dependency or functionality with a controlled substitute having behavior specified by the test.
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  .NET MAUI in ActionA mock implementation is a test or development substitute that provides a controlled implementation of an interface or dependency.
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  gRPC Microservices in GoA mock is a test double that implements an interface and provides programmable responses for controlling a dependency's behavior.
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  Terraform in Depth: Infrastructure as Code with Terraform and OpenTofuA mock is a test substitute that replaces a real infrastructure provider with a fake implementation returning predetermined values without creating real infrastructure.
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  Kafka for ArchitectsA mock is a test double that imitates a dependency and records or verifies interactions with it.
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  Pro ASP.NET Core 7, Tenth EditionA mock object is a test double that imitates a dependency and can provide controlled behavior or interaction verification.

Compare how 21 books explain mocking →

Related concepts

• test doublekind of · A test double is a substitute for a real component or dependency that provides controlled or simplified behavior, or enables interaction observation, during testing.
• integration testused by · An integration test evaluates whether multiple software components, or a component and an external dependency, interact and behave correctly together.
• testcontrasts with · A test is a procedure or check that evaluates behavior using specified inputs or evidence against expected results or criteria.
• spyincludes · A spy is a test double that observes and records interactions with a dependency, optionally retaining or wrapping its underlying behavior.
• unmanaged dependencyuses · An unmanaged dependency is an out-of-process dependency whose interactions are observable by external systems and that is not fully controlled by the application.
• stubcontrasts with · A stub is a stand-in for a component or operation that exposes an interface while substituting simplified, generated, or controlled behavior for its full implementation.

This explainer was generated by Manning's knowledge graph from the text of Functional Programming in JavaScript. The section links point to the parts of the book it draws on.