Describe a scenario where dependency injection helped in writing testable Go code.

Dependency injection is crucial for writing testable Go code. When you inject dependencies into a Go function or struct, you can replace those dependencies with mock objects during testing. This allows you to isolate the code under test and write focused unit tests. By injecting dependencies, you decouple components, making it easier to test individual units without relying on the behavior of other components. In this way, dependency injection promotes unit testing and ensures that the code is testable, maintainable, and reliable.