message: note source of test values
diff: @@ -114,6 +114,8 @@ fn basic() {
  assert_eq(y, 42.0_f32);
  }
  +/// Many of these test values are taken from
  +/// https://github.com/WebAssembly/testsuite/blob/master/conversions.wast.
  fn casts() {
  // f32 -> i8
  test_both_cast::<f32, i8>(127.99, 127);
  