### Question:
NameValidationUtils { public static String checkValidName(String name) { checkArgument(!isNullOrEmpty(name), "name is null or empty"); checkArgument('a' <= name.charAt(0) && name.charAt(0) <= 'z', "name must start with a lowercase latin letter: '%s'", name); for (int i = 1; i < name.length(); i++) { char ch = name.charAt(i); checkArgument('a' <= ch && ch <= 'z' || '0' <= ch && ch <= '9' || ch == '_', "name must contain only lowercase latin letters, digits or underscores: '%s'", name); } return name; } private  NameValidationUtils(); static String checkValidName(String name);  }### Answer:
@Test public void testCheckValidColumnName() { checkValidName("abc01_def2"); assertThrows(() -> checkValidName(null)); assertThrows(() -> checkValidName("")); assertThrows(() -> checkValidName("Abc")); assertThrows(() -> checkValidName("0abc")); assertThrows(() -> checkValidName("_abc")); assertThrows(() -> checkValidName("aBc")); assertThrows(() -> checkValidName("ab-c")); }