Migrating complex, business-critical logic from VB.NET to C# required proof that every function behaved identically in both codebases. Even minor discrepancies could disrupt order processing or fulfillment accuracy.
A Leading US-Based Apparel Distributor Achieves 98% Code Coverage in Legacy-to-Modern Code Migration
Delivered full functional equivalence validation during a critical VB.NET-to-C# migration using AI-assisted tools and xUnit framework.
Talk to Our QA ExpertsSummary
TestingXperts deployed an AI-assisted unit-testing strategy using the xUnit framework, achieving 98%+ line coverage across migrated components. Every conditional path, boundary condition, and entity property was validated, alongside integration touchpoints across methods, databases, and APIs. The approach confirmed functional equivalence, reduced manual regression effort, and lowered long-term maintenance overhead.
Overview
The client is a leading technology-enabled apparel and accessory distributor serving the US and Canadian wholesale markets. They operate a technology-enabled distribution model that depends heavily on robust, accurate backend systems to power order management, logistics, and fulfillment workflows. To support its modernization initiative and to migrate its legacy VB.NET codebase to C#, it needed a testing partner that could validate functional equivalence at every step, ensuring no business logic was lost, altered, or introduced during the transition.
TestingXperts stepped in as the quality engineering partner to validate the migration, establish a verified behavioral baseline, and build a comprehensive xUnit-based test suite for all non-UI code.
Challenges
The client faced multiple challenges in validating the functional equivalence and accuracy of their codebase conversion. Key challenges included:
Functional Equivalence at Risk
100% Unit Test Coverage Requirement
Non-UI code files required exhaustive unit testing, covering all conditional statements, boundary cases, and entity properties, with zero coverage gaps.
Legacy Code Validation Complexity
Test cases needed to run against the original VB.NET code to confirm its behavior before serving as the reference baseline for C# equivalence checks, requiring a dual-track testing approach.
Integration Depth Beyond Mocking
Real-world flows required testing live dependencies, including databases and APIs, to validate end-to-end application behavior across migrated components.
Solutions
TestingXperts delivered a structured, AI-assisted unit testing approach using the xUnit framework. Our approach helped validate the VB.NET-to-C# migration by maximizing test coverage and confirming functional equivalence across the migrated code files.
AI-Assisted xUnit Test Development
Leveraged AI-assisted tools alongside the xUnit framework to accelerate test case authoring, targeting 100% code coverage across all non-UI code files migrated from VB.NET to C#.
Comprehensive Conditional Coverage
All conditional statements, including if/else and case branches, were tested alongside every boundary condition, ensuring no logic path was left unvalidated.
Full Entity Property Assertion
Assertions were written for all properties of given entities, combining extensive positive and negative test scenarios to confirm accurate data handling throughout.
Legacy VB.NET Baseline Execution
Unit test cases were executed against the original VB.NET code first, establishing a verified behavioral baseline that the C# migration was then validated against for equivalence.
Integration Testing of Live Dependencies
Testing extended beyond unit isolation to cover real integrations, databases, APIs, and inter-component flows, ensuring that the full application path was exercised, not just individual units.
How TestingXperts Strategy Helped the Client
100% Functional Equivalence Validated
Automated regression checks significantly reduced the manual testing burden for future releases.
Improved code quality and modularity through thorough unit-level design validation.
Lower long-term maintenance costs through cleaner, well-tested code architecture.
98%+
Line Code Coverage Achieved
30–40%
Reduction in Manual Regression Testing Time
20–30%
Less Effort for Future Enhancements & Refactoring
Turning Migration Risk into Modernization Confidence
TestingXperts ensured that a critical modernization initiative carried no hidden risk by aligning a rigorous, AI-assisted test automation strategy to the codebase migration. By confirming functional equivalence between VB.NET and C#, we helped reduce risk, accelerate QA, and create a cleaner, more maintainable codebase for future growth. The engagement turned a complex migration challenge into a controlled, measurable modernization success.
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