In modern software development, decoupling frontend applications from backend APIs is a common practice that brings numerous benefits, such as better maintainability, scalability, and flexibility. However, when it comes to testing, developers often face a dilemma: Should they rely on the actual backend API or mock the data? 

In this blog post, we will explore the reasons why it is not worth having frontend app tests rely on the backend API and why it is essential to separate them. Additionally, we will delve into effective strategies for achieving test separation in your development workflow.

Why it Is not worth having frontend app tests rely on backend API

1. Dependency on external services

First of all, when frontend tests depend on the backend API, they become tightly coupled to the backend’s availability and performance. Any issues with the backend, such as downtime or slow response times, can significantly impact the frontend testing process, leading to unreliable test results. Additionally, relying on the backend API for testing introduces a potential single point of failure, making test executions susceptible to disruptions.

2. Test environment constraints

In many cases, the backend API may require specific test data or configurations to produce desired outcomes for frontend testing. This reliance can lead to constraints in setting up the test environment and may hinder developers from running tests effectively in isolation. Consequently, developers might spend excessive time preparing and managing the test environment, causing delays in the testing process.

3. Limited Test Scenarios

When frontend tests are directly linked to the backend API, it restricts the scope of test scenarios that can be covered. Complex backend functionalities or edge cases might be challenging to reproduce consistently, resulting in incomplete test coverage. This limitation could lead to undetected bugs and a false sense of confidence in the application’s quality.

4. Increased Test Execution Time

Incorporating backend API calls in frontend tests can significantly increase test execution time. The need to communicate with external services and wait for responses can slow down the testing process, making it less efficient for continuous integration and continuous delivery (CI/CD) pipelines. Faster test cycles are crucial for rapid development and faster feedback loops.

Why is it worth to separate frontend app tests from backend API

1. Isolated testing

Firstly, separating frontend app tests from the backend API allows for isolated testing of individual components or modules. By using mock data, developers can simulate different scenarios without relying on the actual backend. This isolation fosters faster and more reliable testing since external dependencies do not impact test results.

2. Improved test reliability

Next, mocking data empowers developers to create predictable test environments with consistent data scenarios. By doing so, they can ensure that tests produce reliable and repeatable results. This predictability simplifies debugging and reduces false positives or negatives during test executions.

3. Faster feedback loops

Mocking data eliminates the need to make real API calls, resulting in faster test execution times. Shorter test cycles enable developers to receive feedback on their changes more quickly, facilitating faster iteration and improved development speed.

4. Enhanced parallel testing

Last but not least, with tests separated from the backend API, it becomes easier to run tests in parallel. Developers can distribute tests across multiple environments, reducing the overall testing time and allowing for efficient use of available resources.

Now, let’s take a look at how actually to separate these two for a testing process.

How to separate frontend tests from backend API

Use mocking libraries

One of the most common ways to separate frontend tests from the backend API is to use mocking libraries. These libraries allow developers to create mock data and responses for API calls, simulating various scenarios. Popular mocking libraries, such as Jest (for JavaScript) and Mockito (for Java), provide powerful tools to set up mock API responses efficiently.

Implement test doubles

Test doubles, including stubs, fakes, and spies, are essential in separating frontend tests from backend APIs. Stubs act as replacements for real API calls, returning predetermined responses. Fakes are simplified implementations of backend services that provide the necessary data for testing. Spies help in verifying that specific API functions have been called during the test execution.

Dependency injection

By employing the dependency injection principle, developers can inject mock services or data providers into the frontend application during testing. This approach enables seamless swapping of real API services with their mock counterparts, facilitating testing in an isolated environment.

Use service contracts

Implementing service contracts or interfaces between the frontend and backend layers promotes a clear separation of concerns. Frontend developers can then create mock implementations of these interfaces to perform tests without any reliance on the actual backend services.


Test separation, achieved through the use of mock data and proper testing techniques, is a valuable practice in modern software development. By detaching frontend headless app tests from the backend API, developers can achieve improved test reliability, faster feedback loops, and better isolation for testing individual components. Embracing this approach contributes to enhanced overall application quality and facilitates smoother development workflows. As technology advances and development methodologies evolve, investing in test separation will continue to be a crucial aspect of maintaining a robust and efficient software development process.