terraform/vendor/github.com/mitchellh/go-testing-interface/README.md

go-testing-interface

go-testing-interface is a Go library that exports an interface that *testing.T implements as well as a runtime version you can use in its place.

The purpose of this library is so that you can export test helpers as a public API without depending on the "testing" package, since you can't create a *testing.T struct manually. This lets you, for example, use the public testing APIs to generate mock data at runtime, rather than just at test time.

Usage & Example

For usage and examples see the Godoc.

Given a test helper written using go-testing-interface like this:

import "github.com/mitchellh/go-testing-interface"

func TestHelper(t testing.T) {
    t.Fatal("I failed")
}

You can call the test helper in a real test easily:

import "testing"

func TestThing(t *testing.T) {
    TestHelper(t)
}

You can also call the test helper at runtime if needed:

import "github.com/mitchellh/go-testing-interface"

func main() {
    TestHelper(&testing.RuntimeT{})
}

Why?!

*Why would I call a test helper that takes a testing.T at runtime?

You probably shouldn't. The only use case I've seen (and I've had) for this is to implement a "dev mode" for a service where the test helpers are used to populate mock data, create a mock DB, perhaps run service dependencies in-memory, etc.

Outside of a "dev mode", I've never seen a use case for this and I think there shouldn't be one since the point of the testing.T interface is that you can fail immediately.