Client-Side Vs. Server-Side Testing: Full Guide

Client-side and server-side are the two areas where code processing and execution can occur.

In the context of experimentation, you can run testing within the client or user’s browser (client-side) or the server environment (server-side).

Both testing types aim to ensure the website or application functions coherently, providing a positive user experience. You can also integrate them to perform end-to-end testing, covering both frontend and backend aspects.

Client-side testing generally emphasizes the user interface and experience, while server-side testing concentrates on backend processes, databases, and server performance.

Let’s explore their features in more detail.

What is client-side?

Client-side testing is when you experiment, load, or make the most of elements directly within the client’s browser. It focuses on the frontend aspects visible to users, ensuring the user interface is intuitive, responsive, and bug-free.

You apply changes on the client side, meaning the user’s device downloads and executes the experiment code.

Some aspects of client-side testing include:

• User experience (UX) testing: Involves evaluating the website’s usability, design, and overall user satisfaction. This can handle A/B testing, heatmaps, and user feedback analysis.
• Cross-browser and cross-device testing: Ensures consistent functionality and appearance across various web browsers (Chrome, Firefox, Safari, etc.) and devices (desktops, smartphones, and tablets).
• Performance testing: Measures website loading times, responsiveness, and overall speed. Tools like Google PageSpeed Insights and Lighthouse can help make the most of client-side performance.
• Security testing: Focuses on identifying vulnerabilities in client-side scripts (like JavaScript) to prevent issues such as cross-site scripting (XSS) attacks.
• Responsive design testing: Ensures the web layout adjusts appropriately to different screen sizes and orientations.

What is server-side?

Server-side testing involves experimenting, loading, and validating functionalities and processes on the web servers, outside of the end-user’s environment. Server-side generally happens before client-side, and is a more backend and performance-optimized process. You make these changes on the server before the content has reached the user’s device.

It could feature:

• Load testing: Determines the system’s ability to handle a specific load, ensuring the website or app performs under different traffic levels (and potential spikes/surges).
• Database testing: Involves validating data integrity, database schema, and query performance. It ensures efficient data storage and retrieval.
• Security testing: Focuses on server security, including network security, data encryption, and safeguarding against SQL injection and other server-side vulnerabilities.
• API testing: Validates the functionality and reliability of APIs used to communicate with different third-party software systems.
• Performance tuning: Optimizes server-side code, database queries, and configurations to enhance overall application performance.

Both client- and server-side testing are essential parts of a comprehensive testing strategy. Client-side offers insights into user behavior and front-end issues, while server-side focuses on security, consistency, performance, and data integrity.

By combining both approaches, developers can create robust, user-friendly, and secure web applications that provide a smooth user experience across different platforms and devices.

Advantages of client-side testing

• Real user experience: Client-side testing offers insights into how real users interact with the application. It captures actual user behavior, enabling for a more accurate user experience assessment.
• Granular user segmentation: Client-side tools often enable for precise targeting and segmentation, enabling you to test specific user segments with tailored experiences.
• Quick iterations: Since you conduct client-side tests in the user’s browser, developers can quickly iterate and test changes without deploying server updates. This agility is instrumental during the development phase.
• Greater flexibility: You can test user interface changes, content variations, and other client-side elements without touching the server, giving you more flexibility in your experiments.
• Isolates frontend issues: Client-side testing is ideal for spotting issues like layout problems, broken links, or user interaction issues. It helps ensure the user interface is easy to use and responsive.
• A/B testing: Client-side testing enables A/B testing, where different versions of an app or webpage are shown to users simultaneously. This lets developers compare user engagement and conversion rates between designs or features.
• Rich visual feedback: Tools used for client-side testing often provide rich visual feedback, including heatmaps, session recording, and click-tracking to understand user behavior visually.

Advantages of server-side testing

• Security: Enablesrigorous security testing, enabling you to identify and mitigate vulnerabilities before they are exploited. It covers data encryption, authentication, authorization, and more.
• Consistency: Ensures consistent data processing and application behavior regardless of the client device or browser. It helps maintain a unified user experience.
• Performance optimization: Analyzes server response times to make the most of application performance. It includes load testing to ensure the server can handle expected user traffic.
• Data integrity: Verifies the integrity of data storage and retrieval mechanisms, including database transactions. It verifies that data is stored accurately and securely.
• Cross-platform functionality: Confirms backend processes and APIs work across different platforms, devices, and operating systems.

Choosing between client- and server-side testing depends on the goals of your testing efforts, your application’s characteristics, and available resources. It’s also wise to consider user feedback and future growth plans.

Let’s break down some things to keep in mind when deciding.

Focus on goals

If your primary concern is how users interact with your application, using client-side testing is essential. You can use it to test front-end elements like UI, design, and client-side scripts. This helps you understand user behavior, preferences, and pain points.

Server-side testing is vital if you’re concerned about the backend functionality, including data security, server response times, and how the app handles heavy traffic. You can use it to test backend logic, algorithms, or server-side processes.

Consider the nature of the application

Applications that heavily rely on user interactions, dynamic content loading, and real-time updates often benefit from client-side testing. It’s especially useful for those dealing with sensitive data, financial transactions, or complex database operations.

Look at your available resources

Think about the expertise of your teams. Client-side testing may be more convenient if they’re well-versed in front-end technologies—where marketing or product teams usually sit. A development team with solid backend skills can effectively perform server-side (or full stack) testing.

When evaluating testing tools,consider ones that align with project requirements and your team’s knowledge.

Consider comprehensive testing

For a complete understanding of your app, consider using client and server-side testing.

Combining the insights from both methods offers a holistic view of your application’s performance, user experience, and security.

Use feedback and iterate

If your application is already live, use the user feedback. If users report frontend issues, deploy client-side testing. If their concerns are related to data security or transaction failures, lean towards server-side testing.

Remember to continuously iterate and adapt your testing strategy based on feedback and your application’s changing requirements.

Think about future growth

Server-side testing is best for applications expected to scale rapidly, ensuring the backend infrastructure can handle increased traffic and data processing requirements.

Additionally, take into account any planned features and enhancements and what parts they’ll most impact. If they rely on front-end interactions, invest in client-side testing. If they involve complex backend processes, concentrate on server-side testing.

It’s beneficial when you have any of these:

• High participant variability: When there’s a lot of diversity among participants, such as demographics, behavior patterns, or preferences, CUPED experimentation helps you control these differences to get more accurate results.
• Potential confounding factors: If external factors could affect your experiment’s outcomes, like seasonal changes or user-specific characteristics, you can use CUPED to mitigate their impact and isolate the intervention’s actual effect.
  
• Small or subtle effects: When the expected outcome changes are minor or subtle, CUPED can increase the experiment’s sensitivity, so it’s easier to find these minor effects and determine their significance.
• Historical data: You can apply CUPED when you can access relevant historical participant data, as you can use it to create predictive models for outcome variables.
• Resource-intensive interventions: For experiments with lots of resources or high costs, it’s crucial to get accurate results. CUPED ensures the resources you spend on the intervention are justified, as it provides a reliable and precise estimate of its impact.

Understanding the differences and benefits between client-side and server-side testing is crucial for crafting exceptional user experiences and strong backend functionalities. Blending these testing methods is often the best approach to success.

Comprehensive testing is also a significant focus of Amplitude Experiment—your ultimate tool in your journey to data-driven decision-making.

Amplitude empowers you to conduct insightful A/B tests and multivariate experiments, ensuring every tweak you make is backed by real user insights. With its user-friendly interface and powerful analytics, you can effortlessly make the most of user journeys, boost engagement, and drive conversions.

Whether refining the user interface with client-side precision or enhancing server-side security and performance, Amplitude can help amplify your testing efforts.

Discover how your experiments could lead you to unparalleled growth. Contact Amplitude today.