update comment and extend test

internal/terraform/context_apply2_test.go

@@ -510,7 +510,8 @@ output "out" {
 }
 
 func TestContext2Apply_ignoreImpureFunctionChanges(t *testing.T) {
-	// Ensure we're not trying to double-mark values decoded from state
+	// The impure function call should not cause a planned change with
+	// ignore_changes
 	m := testModuleInline(t, map[string]string{
 		"main.tf": `
 variable "pw" {
@@ -527,6 +528,15 @@ resource "test_object" "x" {
   }
 }
 
+resource "test_object" "y" {
+  test_map = {
+	string = "X${bcrypt(var.pw)}"
+  }
+  lifecycle {
+    ignore_changes = [ test_map ]
+  }
+}
+
 `,
 	})