Case Study

Modernizing legacy code in financial services with Diffblue Cover

Faced with legacy code jeopardizing app performance, a leading financial services company turned to AI to quickly enhance code quality. In less than three weeks, Diffblue Cover’s AI-driven unit testing enabled the enterprise to exceed its 80% code coverage target.

750k

lines of code securely covered in one legacy app

51%

code coverage out-of-box

For financial institutions, security and compliance are non-negotiable. Managing sensitive customer data means following strict regulations, with serious consequences for failing to meet these standards, including steep fines, customer loss, and legal issues. Prioritizing security and compliance is key to maintaining trust and safeguarding both the customers’ assets and the institution’s reputation.

Despite this, many financial institutions still depend on outdated software, which poses major challenges. These legacy systems often have security vulnerabilities and lack the adaptability needed to meet evolving regulations and market demands. Developers face the difficult task of modernizing these systems while improving code quality—a challenge that becomes much more manageable with the right tools.

Could artificial intelligence overcome the challenges inherent in legacy software?

Relying on outdated systems was a significant concern for a global company that handles clearing and settlement services for financial markets, processing trillions in securities transactions each day. With over 500 applications driving their operations, the technology and development teams turned to AI-powered unit testing to explore whether it could help them improve code coverage and accelerate their modernization efforts.

Shared priorities across teams:

Both the Technology Director and Cloud Development Director shared four key priorities as they worked to modernize their legacy systems:

Improving Code Coverage: Raising code coverage, particularly in legacy areas, was crucial to maintaining security standards and ensuring smooth upgrades to newer technologies.
Boosting Developer Productivity: Streamlining development processes to enable faster, more efficient work was essential, especially as teams balanced innovation with ongoing maintenance.
Balancing Compliance and Deadlines: Compliance with strict regulations, including meeting a tight 90-day window for security updates, remained a top priority. The teams had to minimize risk while ensuring that code was both compliant and compatible with the latest Java releases.
Maintaining Code Quality: Integrating new tools like Sonar and Bitbucket posed challenges to code quality, but the teams remained focused on keeping quality high, even as changes were implemented.

Overcoming legacy software hurdles with AI-driven testing

The company’s existing software infrastructure posed significant challenges. posed significant hurdles. One key internal application used to settle securities transactions was over a decade old. It relied on outdated technologies like Java 8, Spring 5, Spring Boot 2, XML for configuration, and MyBatis for database connections.

These aging technologies made the app and the applications it supported difficult to maintain, upgrade, and secure. Manual test-writing efforts failed, leaving the app with no test coverage and degrading code quality. The team needed to upgrade the app to meet security standards, but without tests, they risked breaking critical functionality during updates.

Faced with these challenges, the two teams set an ambitious goal: improving the code coverage of this specific app — which contained roughly 750,000 lines of code — by at least 80%.

Out-of-the-box achievements: better than expected

To accomplish this, they piloted Diffblue Cover, our AI-driven testing solution, and the results were impressive: in just over an hour, code coverage increased by more than 50% right out of the box.

Although this app was just a small piece of their overall portfolio, the outcomes were encouraging. Diffblue Cover brought them closer to their goal of modernizing the code and meeting security compliance standards, all without any manual intervention. But, with a target of 80% code coverage, they knew they had to keep pushing to ensure compliance.

Going for goal: Over 80% code coverage in just days

In a focused collaboration, an engineer of Diffblue’s Technical Services Team and one of the financial services company’s developers investigated the factors affecting code coverage. Their objective was clear: increase coverage from 51% to at least 80%, a task they initially estimated would take a team of 5 developers in 6 months to achieve.

To their surprise, the optimization process using Diffblue Cover took less than 3 weeks during which they also identified and removed abandoned and unnecessary code that had been hindering app performance. The end result was a solid 81% code coverage.

This collaboration not only helped the tech and dev teams reach their goal, it also equipped the financial services company with an internal expert who could effectively fine-tune and configure Diffblue Cover as they prepared to implement it across other applications.

Better code quality and security with on-premise AI unit testing

Many applications requiring modernization suffer from poor unit test coverage. If you’ve ever dealt with legacy code, you know it tends to be fragile, difficult to understand, and poorly documented, making the task of writing unit tests both challenging and time-consuming.

Diffblue’s autonomous AI can help. Diffblue Cover accelerates code testing and correction, allowing you to modernize business-critical applications faster and with less risk.

The best part? Diffblue Cover is an on-premise solution, so you won’t have to compromise your enterprise security and privacy posture.

With Diffblue Cover, you can:

Improve code quality and uphold security standards: Use AI-driven unit test generation to expedite development and meet today’s stringent security regulations.
Balance delivery goals and compliance: Alleviate the pressure of prioritizing compliance over new development by equipping teams with the tools needed to meet regulatory requirements.
Improve developer productivity and satisfaction: Empower developers to focus on innovation rather than being bogged down by the constant need to revisit and update code.

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Want to establish the test coverage baseline you need to modernize your applications quickly? Book a demo now to see how quickly Diffblue Cover can boost your code quality.

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