fix test TF infra, add TF manager for testing

testing/testdata/main.tf

@@ -0,0 +1,8 @@
+resource "random_id" "foo" {
+  byte_length = 2
+  prefix      = "test-foo"
+}
+
+output "random_id_decimal" {
+  value = random_id.foo.dec
+}