Refresh before applying test step.

Our test steps handle refreshes very explicitly, which is good. But we
don't actually refresh before applying the step, assuming the previous
step left our state in a good condition.

However, this means that if a config changes the value of a data
source--e.g., for a data source that generates JSON from HCL, as is
common in IAM resources--the data source's value in state won't be
updated before apply, meaning the resources depending on that data
source value will have a stale, incorrect value instead of the one in
the config.

As we advise users to not run Terraform with -refresh=false, this
doesn't mirror the user experience in production and is confusing--I
lost several hours to debugging it.

This PR explicitly runs refresh prior to applying or planning a test
step, so new data source values in the config can be accurately
reflected.

helper/resource/testing_new_config.go

@@ -34,6 +34,16 @@ func testStepNewConfig(t testing.T, c TestCase, wd *tftest.WorkingDir, step Test
 
 	wd.RequireSetConfig(t, step.Config)
 
+	// require a refresh before applying
+	// failing to do this will result in data sources not being updated
+	err := runProviderCommand(t, func() error {
+		wd.RequireRefresh(t)
+		return nil
+	}, wd, c.ProviderFactories)
+	if err != nil {
+		return err
+	}
+
 	if !step.PlanOnly {
 		err := runProviderCommand(t, func() error {
 			return wd.Apply()
@@ -61,7 +71,7 @@ func testStepNewConfig(t testing.T, c TestCase, wd *tftest.WorkingDir, step Test
 	// Test for perpetual diffs by performing a plan, a refresh, and another plan
 
 	// do a plan
-	err := runProviderCommand(t, func() error {
+	err = runProviderCommand(t, func() error {
 		wd.RequireCreatePlan(t)
 		return nil
 	}, wd, c.ProviderFactories)