### Question:
Precondition { public static String notBlank(String value, String fieldName) { if (value == null || value.trim().length() < 1) { throw new IllegalArgumentException("Argument " + fieldName + " cannot be empty."); } return value; }  static T notNull(T value, String fieldName); static String notBlank(String value, String fieldName);  }### Answer:
@Test(expected = IllegalArgumentException.class) public void throwsOnBlankArgument() { Precondition.notBlank(" ", null); }