Unit Test Generator (VakıfBank)

What Problem Does It Solve?

The hard part of retrofitting unit tests onto an existing service isn't the test itself; it's gathering the context the test needs. The public operation, the private methods it calls, its dependencies, entities, DTOs... Collecting all of that by hand is a tedious job you repeat for every method.

Unit Test Generator is a Visual Studio extension (VSIX) I built at VakıfBank to take over that job end to end. It runs on Visual Studio 2022 and later and talks to an LLM hosted inside the bank. Since the context grows once private methods, entities and DTOs are included, it uses the model with the largest context window available in the bank.

How Does It Work?

1. Three selections

In the window that opens, you select, in order:

1. The service file
2. The public operation inside that service
3. The test service file the test will be written to

The extension handles the rest.

2. Trimming the context with Roslyn

The extension doesn't send the code to the model as is. It uses Roslyn to keep only what's needed: comment lines are stripped and the context is narrowed. Everywhere the selected operation can reach is scanned: all private methods, entity methods and DTOs. The scan continues until it has enough scope to exceed the 90% coverage target.

3. Write, run, fix

The model writes the test, and the extension runs it immediately. If the test fails, the error output is fed back to the model and the test is rewritten until it passes. The loop is closed: no developer has to step in along the way.

Service + operation + test file selection
  └─ Roslyn: trimmed context (private methods, entities, DTOs)
       └─ In-house LLM: test generation
            └─ Run the test
                 ├─ success → done
                 └─ fail → regenerate with the error output

Results

95% coverage and above, even on very long, heavily branched methods; the average time per operation is 45 seconds to 1 minute. The developer only makes three selections and reviews the resulting test.