determine of part of string is uppercase, based on requirements

$testcase = 'AKLWC139';

if (ctype_upper($testcase)) {
echo "The string $testcase consists of all uppercase letters.
\n";
} else {
echo "The string $testcase does not consist of all uppercase
letters.\n";
}

?>

This is some code that will check a string and validate if it consists
of all uppercase letters. I am not too familiar with syntax of PHP as
I am learning, ... can someone please show me a way to make this, so
it dives a little deeper into checking, and instead checks to see if
part of the string contains two or more consecutive uppercase
letters? Like

'akwSKWsm' would return positive,.... but 'aKwskWsm' would not.

I don't know how this would work, but it seems approachable. Can
someone pls. help me?

Thank you in advance for assistance. Have a very good day.