message: add a test showing what happens with inputs
diff: +use salsa::Database;
  +
  salsa::query_group! {
  trait HelloWorldDatabase: salsa::Database {
  + fn input(a: u32, b: u32) -> u32 {
  + type Input;
  + storage input;
  + }
  +
  fn none() -> u32 {
  type None;
  }
  @@ -48,6 +55,7 @@ impl salsa::Database for DatabaseStruct {
  salsa::database_storage! {
  struct DatabaseStorage for DatabaseStruct {
  impl HelloWorldDatabase {
  + fn input() for Input;
  fn none() for None;
  fn one() for One;
  fn two() for Two;
  @@ -60,6 +68,10 @@ salsa::database_storage! {
  fn execute() {
  let db = DatabaseStruct::default();
  + // test what happens with inputs:
  + db.query(Input).set((1, 2), 3);
  + assert_eq!(db.input(1, 2), 3);
  +
  assert_eq!(db.none(), 22);
  assert_eq!(db.one(11), 22);
  assert_eq!(db.two(11, 2), 22);
  