/** @param never $value */
function assertNever(mixed $value): never
{
    throw new LogicException();
}

assertNever(123); // this should return error because 123 is not subtype of never

function testMissingCheck(int|string $value): void
{
    if (is_string($value)) {
        echo 'STRING';
    } else {
        assertNever($value); // this should return error, because int is not a subtype of never
    }
}