message: Add StdError Debug/Display tests
diff: @@ -272,4 +272,21 @@ mod test {
  _ => panic!("expect different error"),
  }
  }
  +
  + #[test]
  + fn implements_debug() {
  + let error: StdError = StdError::underflow(3, 5);
  + let embedded = format!("Debug message: {:?}", error);
  + assert_eq!(
  + embedded,
  + r#"Debug message: Underflow { minuend: "3", subtrahend: "5", backtrace: None }"#
  + );
  + }
  +
  + #[test]
  + fn implements_display() {
  + let error: StdError = StdError::underflow(3, 5);
  + let embedded = format!("Display message: {}", error);
  + assert_eq!(embedded, "Display message: Cannot subtract 5 from 3");
  + }
  }
  