Need API Mocking? Our Go-to Guide for Dev Teams

Dan Perovich

WireMock Head of Sales Engineering & Customer Success

June 17, 2024

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Building an app is rarely plain sailing. Inevitable challenges and roadblocks will always appear at some point in the development process, and these can be compounded when teams build an app that relies on third-party APIs.

Third-party APIs are, as the term suggests, outside dev teams’ control, and when they’re unstable, slow to respond, or frequently undergo updates, they can significantly disrupt dev workflows.

The best solution to this potentially detrimental reliance on these APIs is to implement API mocking, which imitates a real API by providing realistic responses to a wide range of static, dynamic, or customized requests.

What is API mocking?

API mocking is a software development process for creating simulated versions of a real API. This mock API can then be used to mimic the behavior of the real API and validate code under real-world conditions even when the actual API is unavailable.

Mock APIs play an important role in providing dev teams with a way to carry on their development and testing activities without being affected by the real API or affecting its live users. Depending on the specific requirements of any use cases, mock APIs can be locally hosted or hosted on a network.

API mocking techniques

There are different types of mock API, and the type you need will depend on the nature of your project and how close to the real thing you need the mock’s responses to be. They can generally be categorized into three types: static mocking, dynamic mocking, and service virtualization.

1. Static mocking: This is the simplest form of mock API and works by creating predefined responses for specific API requests. These responses are hard-coded and do not change, providing a simple yet effective way to simulate API behavior. This technique is particularly useful for testing specific scenarios and ensuring consistent results during development.

2. Dynamic mocking: This type of mock API generates responses based on logic or data, allowing for more flexibility and realism in simulations. Unlike static mocks, dynamic mocks can adjust their responses according to the parameters of the incoming requests. This technique is beneficial for testing a wider range of scenarios, including edge cases and user-specific data interactions

3. Service virtualization: Service virtualization creates a replica of a system that an application depends on to test how well it integrates. It’s a relatively outdated legacy technique that relies on extensive (and expensive) on-premise or cloud architecture to work. This can make it difficult to use and maintain in comparison to more modern alternatives.

API mocking vs stubbing

API stubbing is a technique that uses a dummy or placeholder implementation of API responses as a temporary substitute for the actual API. They’re essentially controllable replacements for existing dependencies within a system which help developers to test their code without interacting with the actual dependency.

While both stubbing and mocking are used to isolate components during testing, there are some differences between the two.

Stubs primarily focus on providing predefined responses to specific input parameters, whereas mocks are designed to validate the interactions or behavior of components.
Stubbing is usually done by defining simulated values at the code level, which means the actual API-calling code will need to be implemented at a later stage, requiring relatively significant changes. With mocking, typically only the API endpoint needs to change, so there is very little difference between the code used during development and the code deployed to production.

Common API mocking use cases

API mocking isn’t just for development. It can be used for a variety of use cases including prototyping, third-party API integration, and overcoming service reliability constraints.

Development, testing, and debugging

The most common application of API mocking is during the app development, testing, and debugging phases of the dev lifecycle. If, for example, a target API is unavailable or unstable, dev teams can use mock APIs to simulate its behavior. This makes it easy to test their app’s logic without waiting for the target API to become available.

By creating mock responses for various endpoints, dev teams can thoroughly test how their application handles different data inputs and error scenarios through chaos engineering, ensuring robustness and reliability before the target API is available. In addition, mock APIs make it easy to isolate issues and focus on solving problems with their code without being affected by a live external API.

API prototyping

API prototyping is the process of building a working model of an API before proceeding with full development. It’s essential for validating ideas and gathering feedback quickly when developing a new app or feature.

Dev teams can utilize API mocking within their prototyping workflows by using mock servers to simulate API interactions without the actual back-end in place. Solutions like WireMock Cloud, for example, take a mock-first approach to API prototyping by making it easy to create mock servers for new and existing APIs and receive realistic responses from them. This allows dev teams to iterate more quickly, from initial planning and design through to testing and deployment, for faster product development.

Learn more about API prototyping:

Integrating third-party APIs

Third-party APIs often come with issues such as rate limits, access restrictions, and unpredictable availability. API mocking allows developers to simulate these third-party services locally, bypassing these limitations during development and testing.

Doing this makes it possible for dev teams to develop and test their apps independently of the third-party API’s limitations. They can, for example, create mocks that mimic the third-party API's responses, thereby making it possible to test how their application will behave under various conditions without any real-world constraints.

Parallel development

Modern software development leans heavily on parallel development: when multiple developers or teams work on different components of the same software product at the same time. API mocking supports parallel development by allowing front-end and back-end teams to work independently without impacting one another.

Front-end developers can, for example, use mock APIs to build and test user interfaces, while back-end developers continue to develop the actual APIs. This decoupling supports the overall development process because teams don’t need to wait for each other to complete their tasks. When the real API is ready, the front-end can seamlessly integrate with it, having already been tested against the mocks.

Unstable and unreliable services

APIs can become unstable, unreliable, or otherwise unavailable during the development lifecycle and present a major roadblock to progress. API mocking provides dev and qa teams with a way to circumvent these roadblocks by allowing developers and testers to create a stable and predictable environment.

Mocks can be used to simulate the API's expected behavior, enabling developers and testers to continue their work without interruptions. This is particularly useful for ensuring that the application can handle downtimes effectively and that any fallback mechanisms work correctly.

What’s the point of mocking APIs?

High-level discussion of API mocking benefits before covering some specific examples:

Faster CI/CD: API mocking accelerates CI/CD by providing stable and predictable API responses, eliminating dependencies on live services. This ensures that automated testing runs smoothly and makes it easier for issues to be identified and resolved.

Cross-platform integration: API mocking facilitates seamless cross-platform integration by simulating API responses across different environments and platforms. This allows developers to test how their applications interact with various systems without relying on live services.

Immediate validation: With API mocking, developers can validate their code against expected API responses immediately, even if the actual API is not yet available or is still under development. This instant feedback loop enables quicker detection and correction of errors, improving code quality and reducing development time.

Improving stability: Actual APIs, especially third-party APIs, can be unstable or undergo changes that disrupt tests. Mocks provide a consistent interface that doesn’t change unless explicitly modified by the developers. They’re also much faster because they return predefined responses.

More cost-efficient: Dev teams can significantly reduce their overheads by using API mocks vs. accessing third-party APIs, especially those with usage fees or rate limits. Solutions like WireMock Cloud can be used at scale without incurring additional costs, making it an economical choice for projects small and large. ‍

Use WireMock Cloud for mocking APIs

As any developer will know — the digital age runs on APIs.

Every piece of software built today either is an API or uses one. They’ve become a critical component of digitization and, as a result, there has been an explosion in API utilization. At the same time, a market for API mocking tools and solutions has also grown to make API mocking accessible to dev teams of all sizes without the need to build infrastructure.

At WireMock Cloud, we provide a powerful, open-source solution for mocking the APIs that you depend on in your day-to-day workflows. Built on the open source WireMock library—the leading enterprise-grade mocking framework—we offer a hosted solution for API prototyping, mock-driven development, response testing, scenario testing, and more.

WireMock Cloud supports a wide range of API mocking use cases where developers depend on third-party APIs, with features such as:

If you’re interested in learning more, you can try it out and begin mocking instantly by signing up for our free forever account.

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