[SalesForce] the Username and Password when I CLONE a sandbox

If this only errors in the 1 box it's most likely that the user actually exists out side of the test class in that specific org. Test this by printing the user to the debug log with system.debug and then querying to see if it exists.

Regardless of the reason, the issue is self explanatory. Here is some sample logic I've used in the past.

public static User newUser() {
    Id profileId = [
        SELECT Id
        FROM Profile
        WHERE Name = 'System Administrator'
    ].Id;

    String uniqueEmail = String.valueOf(Math.round(Math.random()*1000)) +
        string.valueOf(System.now().format('ddMMYYYhhmmss')) +
        '@' + URL.getSalesforceBaseUrl().getHost();

    User result = new User(
        FirstName = 'Grumple',
        LastName = 'Frillskin',
        Alias = 'gfrilly',
        Email = uniqueEmail,
        UserName = uniqueEmail,
        EmailEncodingKey='UTF-8',
        LanguageLocaleKey='en_US',
        LocaleSidKey='en_US',
        TimezoneSidKey='America/Los_Angeles',
        ProfileId = profileId
    );

    return result;
}

Notes:

• Avoid generic terms such as "Test" or "Sample"
• Use the org url so that the chance of the user existing outside this org is minimal
• Use random number + time to make the username as unique as possible
• FirstName, LastName, Email, and Alias do not need to be unique\
• Using the host url does run the risk of duplicates in the event of a refresh (as you will not be on the same host and someone else on your new host may be using similar logic) consider adding the org ID as well.