Tests string formatting with String::format().
@dataProvider providerFormat
string $string: The string to run through String::format().
string $args: The arguments to pass into String::format().
string $expected: The expected result from calling the function.
string $message: The message to display as output to the test.
function testFormat($string, $args, $expected, $message) {
$result = String::format($string, $args);
$this
->assertEquals($expected, $result, $message);
}