What are some best practices for testing and handling edge cases when working with strings in PHP?

When working with strings in PHP, it's important to test and handle edge cases to ensure the code behaves as expected in all scenarios. This includes testing for empty strings, strings with special characters, and strings with different character encodings. One best practice is to use functions like `strlen()` and `mb_strlen()` to accurately determine the length of a string, especially when dealing with multibyte characters.

// Example of testing and handling edge cases with strings in PHP

$string = "Hello, World!";

// Check if the string is empty
if (empty($string)) {
    echo "String is empty";
}

// Check the length of the string using mb_strlen for multibyte characters
$length = mb_strlen($string, 'UTF-8');
echo "String length: $length";

// Check if the string contains a specific character
if (strpos($string, '!') !== false) {
    echo "String contains an exclamation mark";
}