Hands-On Dependency Injection in Go

Stubs

Sometimes referred to as test doubles, stubs are fake implementations of a dependency (that is, an interface) that provides a predictable, usually fixed result. Stubs are also used to help exercise code paths, such as errors, that otherwise might be very difficult or impossible to trigger.

Let's look at an example interface:

type PersonLoader interface {   Load(ID int) (*Person, error)}

Let's imagine that the production implementation of the fetcher interface actually calls an upstream REST service. Using our previous types of tests list, we want to test for the following scenarios:

• Happy path: The fetcher returns data
• Input error: The fetcher fails to find the Person we requested
• System error: The upstream service is down

There are ...