don't check outputs for legacy tests

The legacy tests never had to account for outputs in the plan. This path
is not used outside of old builtin test provider, so just work around
the output changes until we remove this completely.

helper/resource/testing_config.go

@@ -115,9 +115,17 @@ func testStep(opts terraform.ContextOpts, state *terraform.State, step TestStep)
 	if stepDiags.HasErrors() {
 		return state, newOperationError("second follow-up plan", stepDiags)
 	}
-	empty := p.Changes.Empty()
+	empty := true
 	newState := p.State
 
+	// the legacy tests never took outputs into account
+	for _, c := range p.Changes.Resources {
+		if c.Action != plans.NoOp {
+			empty = false
+			break
+		}
+	}
+
 	if !empty {
 		if step.ExpectNonEmptyPlan {
 			log.Printf("[INFO] Got non-empty plan, as expected:\n\n%s", legacyPlanComparisonString(newState, p.Changes))