Unit tests are designed to test the smallest parts of an application, called units. These are typically individual functions or methods within a software component. The primary goal of unit testing is to validate that each unit of the software performs as expected.
* D. The correctness of a specific function of a software component: Unit tests focus on testing individual functions or methods to ensure they produce the correct results given various inputs.
The other options are incorrect:
* A: Syntactical correctness is checked by the compiler or interpreter, not unit tests.
* B: Formal validity of a service's external REST API is usually tested with integration or API tests.
* C: Integration tests focus on the integration of multiple components.
* E: Performance tests (throughput, load capacity, latency) are not part of unit testing.
References:
* Wikipedia - Unit Testing