Golang interfaces & mocking

Question

I\'m having hard times writing unit tests in Go due to external libraries which don\'t expose an interface (therefore not mockable) but only pure functions. Even big ones like G

Answer 1

IMO this is a super common solution and strikes a good balance between maintainability and testability.

The way I think of this is that your code is programming to an interface, and there just happens to be two implementations:

• "prod" version ie the library that you're testing
• test version, a stub that implements the interface

With this approach, a stub can only verify up to your service and its dependencies boundary along the contract of the interface, it assures very little or nothing about your components collaboration/integration with the library that's being stubbed. In my experiences this approach works awesome and is my personal preference. I have found it to be important though to have 1 or 2 higher level tests making sure that your component can successfully initialize and interact with the "prod" version of the library.

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Plug:

I've written about this exact issue https://medium.com/dm03514-tech-blog/you-are-going-to-need-it-using-interfaces-and-dependency-injection-to-future-proof-your-designs-2cf6f58db192