message: Add more string formatting tests
diff: @@ -1314,15 +1314,19 @@ mod test {
  let a = Complex::new(1.23456, 123.456);
  assert_eq!(format!("{}", a), "1.23456+123.456i");
  assert_eq!(format!("{:.2}", a), "1.23+123.46i");
  - assert_eq!(format!("{:.2E}", a), "1.23E0+1.23E2i");
  assert_eq!(format!("{:.2e}", a), "1.23e0+1.23e2i");
  + assert_eq!(format!("{:+020.2E}", a), "+0001.23E0+001.23E2i");
  - let b = Complex::new(128, 255);
  + let b = Complex::new(0x80, 0xff);
  assert_eq!(format!("{:X}", b), "80+FFi");
  assert_eq!(format!("{:#x}", b), "0x80+0xffi");
  - assert_eq!(format!("{:+#b}", b), "+0b1000000+0b1111111i");
  + assert_eq!(format!("{:+#b}", b), "+0b10000000+0b11111111i");
  assert_eq!(format!("{:+#16o}", b), " +0o200+0o377i");
  assert_eq!(format!("{:+#016x}", b), "+0x00080+0x00ffi");
  +
  + let c = Complex::new(-10, -10000);
  + assert_eq!(format!("{}", c), "-10-10000i");
  + assert_eq!(format!("{:016}", c), "-0000010-010000i");
  }
  #[test]
  