As software development accelerates with the rise of AI and evolving frameworks, developers face new challenges in unit testing and maintaining clean, reliable code. In 2025, the landscape of testing is more complex than ever. Here are the top five testing challenges developers will encounter—and practical solutions using a combination of tools and best practices.
1. AI Bias in Test Data
With AI integration in applications, one of the biggest challenges is ensuring that tests are free of bias. AI models can inherit biases from training data, leading to inaccurate or unfair results. Developers need to create unit tests that catch these biases early using tools to mock different scenarios and control test environments.
Another growing issue is the risk of using outdated or incorrect APIs generated by AI. Developers who rely on auto-generated code snippets from GenAI tools may unknowingly introduce wrong or deprecated API calls into their applications, leading to faulty test scenarios.
The Problem: Incorrect API calls can lead to runtime errors, unexpected behaviors, and security vulnerabilities. For instance, a developer using a GenAI-generated snippet may call a deprecated API without realizing it, which could break the application when the API is removed.
The Solution: Implement validation tests to verify that API calls used in your code are up to date. Tools like Typemock can mock these API calls to simulate different versions and behaviors, ensuring that your application handles updates correctly and remains stable.
Alternatively, use static analysis tools to identify deprecated APIs and ensure best practices are followed.
2. Maintaining Legacy Codebases
Legacy systems in C++ and .NET remain a significant challenge for developers. These systems are often fragile, making updates risky. Testing becomes even more difficult when documentation is outdated or missing.
The Solution: Use Typemock Isolator++ for C++ and Isolator for .NET to mock dependencies in legacy code without altering the codebase. This enables safer testing and modernization of applications without breaking existing functionality.
In .NET, you can also leverage the Suggest feature in Typemock, which uses AI to automatically generate unit tests for your code. This feature helps developers get a head start on covering their code with tests, especially in large legacy projects where creating tests manually can be time-consuming.
For C++, consider using Google Test to complement mocking frameworks.
Code Example:
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#include <Isolator5.h> #include <gtest/gtest.h> class LegacySystem { public: virtual int GetData() { return 42; } }; TEST(LegacyCodeTest, MockLegacySystem) { // Arrange auto a = Isolate(); auto legacyFake = a.Fake.Instance<LegacySystem>(); a.CallTo(legacyFake->GetData()).WillReturn(100); // Act int data = legacyMock->GetData(); // Assert EXPECT_EQ(data, 100); } |
3. Keeping Tests Relevant with Frequent Code Changes
As development cycles get shorter, the codebase changes frequently. AI tools are often used to assist in writing or fixing code. These tools are typically 80% accurate—but it’s the 20% that no one notices that can introduce bugs or unexpected behavior. This makes it even more crucial to have a strong testing framework in place.
At Typemock, we follow a strict rule: If you don’t understand the code, you can’t use it. When relying on AI-generated code snippets, developers must ensure that every new piece of code is covered by unit tests to verify it works as expected.
The Solution: Use Typemock Isolator to create comprehensive tests for AI-generated code. Additionally, tools like JetBrains Rider and ReSharper offer code insights to identify risky changes early.
Code Example:
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[TestMethod] public void Should_VerifyAiGeneratedCode_WorksAsExpected() { // Arrange var service = Isolate.Fake.Instance<MyService>(); // AI-generated code snippet assumed to call a method that returns a value Isolate.WhenCalled(() => service.GetValue()).WillReturn(42); // Act var result = service.GetValue(); // Assert Assert.AreEqual(42, result); } |
4. Balancing Speed and Coverage
Fast-paced development requires fast tests, but there’s often a trade-off between speed and test coverage. Focusing only on critical paths may leave edge cases untested, while extensive tests can slow down deployment.
The Solution: Use Typemock’s mocking frameworks to achieve both speed and coverage. Mocking external dependencies reduces test execution time, while maintaining thorough coverage of critical areas.
For faster builds, use CI/CD tools like GitHub Actions or Azure DevOps to automate and parallelize test execution.
Code Example:
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[TestMethod] public void Should_RunTestQuickly_WithMockedDependencies() { // Arrange var dbContext = Isolate.Fake.Instance<DatabaseContext>(); Isolate.WhenCalled(() => dbContext.GetData()).WillReturn(new List<string> { "data1", "data2" }); var service = new MyService(dbContext); // Act var result = service.GetProcessedData(); // Assert Assert.AreEqual(2, result.Count); } |
5. Ensuring Test Data Privacy and Security
With stricter data privacy regulations, using real customer data in tests is risky. Developers must find ways to test applications without compromising sensitive information.
The Solution: Use Typemock to mock sensitive data and simulate real-world scenarios without exposing actual data. Additionally, tools like DataDog and Splunk can help monitor and secure test environments.
Code Example:
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[TestMethod] public void Should_UseMockData_ForPrivacyCompliance() { // Arrange var customerService = Isolate.Fake.Instance<CustomerService>(); Isolate.WhenCalled(() => customerService.GetCustomerData()).WillReturn(new Customer { Name = "John Doe", Email = "anonymous@example.com" }); // Act var customer = customerService.GetCustomerData(); // Assert Assert.AreEqual("John Doe", customer.Name); Assert.AreEqual("anonymous@example.com", customer.Email); } |
Conclusion
The future of software development brings exciting advancements—but also new challenges for testing. Developers must stay ahead by adopting modern testing tools and practices. Combining Typemock and other tools can help address these challenges head-on, ensuring that your applications remain robust, secure, and ready for the future.
Ready to tackle your testing challenges? Download Typemock’s Isolator and start transforming your testing process today!
