add vendor

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

@@ -0,0 +1,52 @@
+# 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](http://godoc.org/github.com/mitchellh/go-testing-interface).
+
+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.