helper/resource: improve logging and output for tests

helper/resource/map.go

@@ -62,6 +62,12 @@ func (m *Map) Apply(
 	if s.ID == "" {
 		result, err = r.Create(s, d, meta)
 	} else {
+		if r.Update == nil {
+			return s, fmt.Errorf(
+				"Resource type '%s' doesn't support update",
+				s.Type)
+		}
+
 		result, err = r.Update(s, d, meta)
 	}
 	if result != nil {

helper/resource/testing.go

@@ -202,9 +202,11 @@ func testStep(
 	}
 
 	// Plan!
-	if _, err := ctx.Plan(&terraform.PlanOpts{Destroy: step.Destroy}); err != nil {
+	if p, err := ctx.Plan(&terraform.PlanOpts{Destroy: step.Destroy}); err != nil {
 		return state, fmt.Errorf(
 			"Error planning: %s", err)
+	} else {
+		log.Printf("[WARN] Test: Step plan: %s", p)
 	}
 
 	// Apply!