[User Story] Expand basic tests for HelloWorld.sayHello method

[jody]

As a maintainer,
I want the basic tests for the sayHello method in HelloWorld to be more robust,
so that I can have greater confidence when I use them for regression testing after I make updates to the code.

The existing tests for sayHello are limited, each uses only exactly length 5 strings of lower case letters from the first 128 characters of UTF-8.

It would be beneficial to have tests that check more cases, such as very long strings and strings with characters outside of the 26 lower-case letters.

References:
https://en.wikipedia.org/wiki/UTF-8

Acceptance Criteria

• HelloWorldTest provides minimum of 10 tests for unique non-null and non-empty strings.
• HelloWorldTest provides a test for a string of at least one-quarter the maximum possible length string in Java.
• HelloWorldTest provides tests for a strings using non-printing ASCII compatible characters.
• HelloWorldTest provides tests for a strings using multi-byte UTF-8 characters.