Why Application Testing Is Essential for Its Success

As a tester, I often hear the question: “Why do we need additional testing if everything already works?”
The truth is that even the best-written code can contain defects that only reveal themselves in real-life usage — under higher traffic, on specific device configurations, or due to unusual user behavior. A single critical issue in payments, login, or order processing can halt sales within hours and seriously damage a brand’s reputation. That’s why application testing is not just a formality, but an essential stage of the entire software development process.

At the beginning, it’s worth answering a fundamental question:

What does a tester actually do?

A tester’s role is to verify whether an application works as intended, is secure, stable, and user-friendly. It’s not only about “finding bugs,” but above all about ensuring that the product meets business requirements — meaning it truly solves the problems it was designed to address. A tester looks at the application through the user’s eyes, assessing whether it is intuitive, easy to learn, and practical in everyday use.

Testing is not limited to “clicking through” an application once it’s finished. It also includes requirements analysis, design reviews, consultations, and workshops with the team before development even begins.

Accessibility is another crucial aspect. A good application should be usable by people with disabilities as well. Testers verify, among other things, screen reader support, sufficient color contrast, correct heading structure, and alternative text for images. A tester is an integral member of the project team, working closely with UX/UI designers, developers, and Product Owners (the people responsible for the final shape of the product on the client’s side) to deliver the highest possible quality.

Can developers test the application themselves?

They can — and often do — especially when it comes to unit and integration tests. However, developer testing serves a different purpose: its main goal is to quickly verify whether new changes break existing system logic.

Broader testing — such as system, acceptance, usability, or performance testing — requires an independent perspective and focuses on aspects that testers and end users interact with daily.

Why shouldn’t developers test everything themselves? Because it’s easy to miss issues that only appear during real-world usage or when different system components don’t work together perfectly. Developers primarily focus on correct implementation and technical aspects of the code. Testers, on the other hand, view the product holistically, from the user’s perspective, validating real usage scenarios and unpredictable situations that may occur in a production environment.

Types and levels of testing — who tests what?

Tests can be divided into:

Types:

• Functional
• Non-functional

Levels:

• Unit
• Integration
• System
• Acceptance

Types of tests

Functional tests verify whether the system does what it is supposed to do (e.g., adding a product to the cart, proceeding to payment). These are usually performed by testers, who assess whether functionalities meet user needs.
Example: Is a discount applied correctly during checkout?

Non-functional tests focus on how the system works rather than on individual features (performance, security, usability, accessibility). These are mainly performed by testers, although developers may conduct preliminary checks.
Example: Does the application load in under two seconds under heavy traffic?

Levels of testing

Testing levels define the complexity at which the system is tested: individual functions, cooperation between modules, the entire system, or a product ready for end users.

• Unit tests verify the smallest pieces of code (e.g., individual functions). They are typically performed by developers to ensure correctness before combining components.
• Integration tests verify how modules work together (e.g., backend with database, payment system with order processing). These are usually performed by testers in cooperation with developers.
• System tests cover the fully integrated application, verifying both functional and non-functional aspects such as performance and security. These are primarily conducted by testers, sometimes with developer support.
• Acceptance tests (UAT) verify whether the final product meets business needs and client expectations. They are usually performed by end users or business representatives with Product Owners. Testers may assist but do not lead this phase.

What does application testing look like step by step?

The testing process can consist of many stages and may vary depending on the chosen methodology (traditional, agile, incremental, or iterative), available time, and budget.

It is often said that “testing is context-dependent” — one of the core principles of ISTQB (International Software Testing Qualifications Board). This means that testing approach, scope, and priorities depend on the type of application, its environment, business goals, and available resources.

There is no universal test plan that fits every project. What is critical in a banking application (e.g., security, transaction correctness) may be less important in a simple informational app — and vice versa. Therefore, testing strategies must always be tailored to the specific product, its users, and business objectives. However, in most cases, the process includes the following stages:

1. Requirements analysis

Testing begins long before the first line of code is written. From a tester’s perspective, this is the most important stage, as it helps understand what the application is meant to be, what problems it solves, and which business and technical requirements it must meet. Testers review documentation (requirements, mockups, user stories) and often participate in workshops with clients or internal teams.

In-depth analysis helps identify critical business scenarios — the features most important to users and the business (e.g., registration, purchase, payment, form submission). It also allows testers to spot gaps, inconsistencies, and potential issues before development begins.

Better understanding of the application = better tests = higher quality
Higher quality = greater chance of business success

2. Test planning

After analysis comes test planning — defining what will be tested, how, when, and where. A test plan specifies, among other things:

• Test scope (critical vs. less important areas),
• Schedule (who tests what and when),
• Test environment (devices, operating systems, browsers, test data).

A well-prepared test plan organizes activities, helps track progress, and enables effective risk management. It answers a key question: “What exactly will we verify before releasing the application to users?”

3. Test case design

Next comes the design of test scenarios and test cases.

Test scenarios are high-level descriptions of functionality or business processes from the user’s perspective (e.g., “User registers an account and confirms email”). They outline possible actions and expected outcomes.

Test cases are more detailed and time-consuming to create. They include step-by-step instructions and specific test data needed to verify a feature. Well-designed test cases help quickly identify issues, avoid chaos during testing, and simplify retesting and regression testing — ensuring consistency and repeatable quality across releases.

4. Test implementation (test assets and environment setup)

This stage involves preparing the test environment and test assets (scenarios, test data, and supporting materials).

In practice, this includes:

• Preparing hardware and infrastructure (servers, network configuration),
• Installing and configuring required software (operating systems, applications, databases),
• Configuring the application itself (external integrations, test modes),
• Preparing test data (accounts, products, transactions).

For mobile applications, it is especially important to consider different devices, OS versions, screen resolutions, and network conditions. The goal is to reflect the production environment as closely as possible so that test results are reliable.

5. Test execution

This is where actual testing takes place. Planned tests are executed, and results are compared with expected outcomes to identify defects (“bugs”). Both verification and validation are performed.

Tests can be manual or automated and include functional and non-functional testing (performance, security, usability, accessibility). Both positive scenarios (expected correct behavior) and negative scenarios (invalid input, unauthorized actions, lack of resources) are tested.

Retesting and regression testing

After fixes are applied, retesting confirms that issues have been resolved. Regression testing ensures that fixes haven’t broken existing functionality. All tests, retests, and regressions should be documented, as reports help teams track readiness and remaining work.

Final tests and acceptance

At the end, the application goes through acceptance testing (UAT), often with clients or business users. The final product is validated once more. If everything meets expectations, the application is released to production.

6. Test closure

The final stage includes closing testing activities, archiving test assets, shutting down test environments, and analyzing lessons learned for future improvements.

Application testing tools

Examples of tools commonly used by testers include:

· Postman – used to verify an application’s API by sending requests. It allows testers to check whether the API works correctly and whether it returns values in the expected format.

· Chrome DevTools – a set of tools for working with web applications, built directly into the Google Chrome browser. It enables code analysis, error tracking, inspection of API communication, and performance measurement, which helps quickly diagnose issues.

· JMeter – allows simulation of traffic from many users at the same time and makes it possible to verify whether the system can handle, for example, a sudden spike in traffic after a marketing campaign.

· TestRail / TestLink – tools for creating and managing test cases. They facilitate test planning and result reporting. When properly integrated, they allow test cases to be reported directly in project tracking tools such as Jira.

· Jira / Azure DevOps – tools that support project management and the software testing process. They enable tracking work progress, reporting defects, and monitoring the bug-fixing process. In addition, they support communication between testing teams, development teams, Project Managers, Product Owners, and other project stakeholders.

· BrowserStack – a platform used for testing web and mobile applications on real devices. It makes it possible to verify application compatibility across many different devices and operating systems without the need to physically own each one.

· WAVE – a tool used to evaluate website accessibility in accordance with WCAG guidelines. It helps identify issues related to color contrast, font size, heading structure, and alternative text for images.

· NVDA / JAWS / TalkBack / VoiceOver – screen readers that support blind and visually impaired users. They enable reading the content of websites, applications, and documents using speech synthesis, as well as navigation via keyboard, gestures, or voice commands, and integration with braille displays. They are essential tools for testing the accessibility of websites and applications.

Why test an application?

A well-executed testing process reduces failure risk, improves product quality, increases user satisfaction, and strengthens brand trust. Fixing issues before release is significantly cheaper than responding to problems after deployment — when costs include not only development time but also financial and reputational losses.

No testing = risk to both the product and the company’s reputation.
Quality assurance is not a formality — it is real business value.

Summary

Application testing is not a one-time phase but a continuous process accompanying the project from initial requirements to deployment. Thanks to testing, applications are stable, secure, and ready for real-world use.

If quality matters to you, testing is not an option — it’s a necessity.