In regulated industries like finance, medical, automotive, aviation, or industrial vehicles, the term “legacy application” is often misunderstood. It doesn’t mean “outdated” or “ready for retirement.” It means foundational, the kind of system that quietly powers mission-critical processes behind the scenes.
For example, in finance, these legacy applications are everywhere. From back-office trade reconciliation tools built in the early 2000s to loan origination software developed on MFC or WinForms, they continue to run core business operations. And while flashy fintech apps dominate headlines, most large financial institutions still rely on legacy desktop software every day.
As a result, the need for robust legacy application testing has never been more urgent. Yet testing them presents unique challenges, especially at the GUI level. Teams must find ways to improve quality, meet compliance demands, and deliver software updates without the option to rewrite from scratch. That’s where Squish for Windows comes into play.
What Is a Legacy Application, Really?
A legacy application is a software built with older technologies or frameworks that are no longer actively developed or commonly used in modern software stacks. Think Win32, MFC, VB6, or early versions of .NET. These applications often run only on desktop operating systems (frequently Windows), and may lack APIs, documentation, or access to the original source code.
But what truly defines a legacy application isn’t its age, it’s its entrenchment. These systems are deeply embedded in an organization’s daily operations, handling critical workflows like customer account management, loan processing, or compliance reporting.
Despite their age, legacy applications are often extremely stable. They've been refined over years, and their behavior is well understood internally. But they're also brittle: small changes can have unintended consequences, and the risk of regression is high. That’s why thorough, repeatable testing is so important.
These legacy applications often have decades of domain knowledge embedded in them. They’ve been customized, validated, and hardened through years of use.
So, to summarise, a legacy application typically refers to software that:
- Was built using older technologies, frameworks, or programming languages (e.g., COBOL, MFC, VB6, WinForms).
- Runs on traditional operating systems like Windows XP, 7, or sometimes even Windows 10/11 in compatibility modes.
- Has limited or no API surface for integration or testing.
- Cannot be easily modified or migrated due to business, regulatory, or technical constraints.
Why Legacy Systems Still Prevail in Regulated Industries
While many industries have migrated to cloud-native applications and microservices, some sectors still continue to rely on legacy systems. This isn’t due to reluctance, it’s often a strategic decision. Beneath sleek mobile apps and AI-powered chatbots, the real work still happens in legacy applications: systems built years or even decades ago that continue to power core banking, trading, risk management, and compliance operations. And they require modern quality assurance just as much as any new software, if not more.
Replacing a legacy core system is a monumental task. The costs are high, the risks are significant, and the time-to-value is long. These systems often involve complex business logic, regulatory history, and interdependencies that make them resistant to change.
Moreover, regulatory pressure reinforces their longevity. For example, in banking, systems must maintain a proven audit trail and meet strict standards for data integrity and reporting. Legacy applications, which have already been validated and audited over the years, offer a kind of stability that’s hard to replicate in newer software.
Here are some of the reasons why companies keep relying on legacy applications:
- Regulatory stability trumps technical novelty
Compliance-heavy environments prioritize stability, auditability, and predictability over rapid innovation. If a legacy system works, and regulators approve of it, institutions are hesitant to replace it. - Migration is expensive and risky
Rewriting or replacing a mission-critical system isn’t just a technical challenge. It’s a business risk that involves data integrity, retraining staff, and ensuring regulatory continuity. - They’re deeply integrated into business processes
Legacy apps often connect to downstream systems, internal workflows, or external interfaces. Unwinding that complexity is rarely straightforward. - They work
It’s not uncommon for a 15-year-old mortgage platform or reconciliation tool to continue doing its job flawlessly, making its eventual replacement more of a cost issue than a technical one.
The Testing Dilemma: GUI Is the Only Way In
For many QA teams, the biggest challenge with legacy application testing is access. These systems often lack a modern API, meaning you can’t simply plug them into an automated testing framework. Without source code or test hooks, the only reliable way to validate functionality is through the Graphical User Interface (GUI), the same way end users interact with the application.
Legacy apps often present a black-box challenge for QA teams:
- There’s no public API for automated testing
- The source code may be lost, unavailable, or off-limits
- The UI was never designed for automation or accessibility
Manual testing might have worked in the past, but it doesn’t scale, and it’s not suitable for audit-ready environments. It is time-consuming, error-prone, and unsustainable, especially in organizations moving toward faster release cycles or continuous delivery models. Regulated institutions, in particular, need testing that is not only repeatable but also well-documented and audit-friendly.
So how do you test, for example, a legacy Windows app like a modern product? You start with the interface—the only layer available.
And that’s where GUI test automation becomes essential. But not just any automation tool will work.
How Squish Solves the Legacy Testing Problem
Squish is designed to meet the specific challenges of GUI testing for legacy desktop applications. It allows QA teams to automate interactions with the interface itself, without modifying the application or accessing the code behind it.
Where other tools rely on image recognition or superficial clicks, Squish dives deeper. It hooks into the application’s object model, enabling precise, reliable interactions with UI elements.
Instead of relying on screen pixels, Squish identifies each button or field by its underlying properties—like class name, object ID, or role, making the tests more stable.
For legacy Windows applications, whether you're working with classic MFC-based software, .NET WinForms UIs, or even Qt-based systems, Squish provides robust Windows application testing by recognizing controls, fields, buttons, and dialogs just like a real user would. It combines human-like interaction with the consistency and repeatability of automation.
Better still, Squish fits into modern QA workflows. You can integrate it with CI/CD pipelines, use behavior-driven development (BDD) to express tests in plain language, and generate rich reports that stand up to internal audits or external regulatory reviews.
For financial institutions, this means:
- Faster regression cycles
- Improved test coverage
- Reduced manual workload
- Greater confidence in release quality
All without rewriting a single line of the application itself.
Bringing Modern QA to Traditional Systems
Legacy software is not going away. But that does not mean quality assurance has to stay stuck in the past. With the right tools, legacy applications can benefit from modern testing strategies like automation, continuous integration, and traceable test coverage.
The push for agility and automation in QA is not limited to greenfield development. Legacy applications, particularly in regulated industries, deserve the same level of attention and rigor. After all, these are the systems handling the money, the compliance, the customer trust.
Squish for Windows offers a pragmatic path forward. By enabling automated, robust GUI testing for legacy desktop software, it bridges the gap between yesterday’s systems and today’s testing demands.
If your organization is still testing a legacy app manually, or struggling to validate changes confidently, it’s time to modernize the process without replacing, rewriting, rearchitecting, or replatforming the product.
Explore Squish for Windows and discover how you can bring automation to your most critical Windows application testings.
