Add package documentation about the binary test driver

Author: paultyng

acctest/doc.go

@@ -0,0 +1,31 @@
+package acctest
+
+// Package acctest provides the ability to opt-in to the new binary test driver. The binary
+// test driver allows you to run your acceptance tests with a binary of Terraform instead of
+// a source code version included with the testing code. This allows for a number of important
+// enhancements, but most notably a more realistic testing experience and matrix testing
+// against multiple versions of Terraform CLI. This also allows the SDK to be completely
+// separated, at a dependency level, from the Terraform CLI.
+//
+// The new test driver must be enabled by initialising the test helper in your TestMain
+// function in all provider packages that run acceptance tests. Most providers have only
+// one package.
+//
+// In v2 of the SDK, the binary test driver will be mandatory.
+//
+// After importing this package, you can add code similar to the following:
+//
+//   func TestMain(m *testing.M) {
+//     acctest.UseBinaryDriver("provider_name", Provider)
+//     resource.TestMain(m)
+//   }
+//
+// Some providers already have a TestMain defined, usually for the purpose of enabling test
+// sweepers. These additional occurrences should be removed.
+//
+// Initialising the binary test helper using UseBinaryDriver causes all tests to be run using
+// the new binary driver. Until SDK v2, the DisableBinaryDriver boolean property can be used
+// to use the legacy test driver for an individual TestCase.
+//
+// It is no longer necessary to import other Terraform providers as Go modules: these
+// imports should be removed.