function isConstantcase( value ) {
	return (
		isString( value ) &&
		value === constantcase( value )
	);
}
Tests if a value is a constantcase string.

@param {*} value - value to test
@returns {boolean} boolean indicating whether a value is a constantcase string

@example
var bool = isConstantcase( 'BEEP_BOOP' );
// returns true

bool = isConstantcase( 'beep_boop' );
// returns false

bool = isConstantcase( 'BEEP-BOOP' );
// returns true

bool = isConstantcase( 'beep boop' );
// returns false

bool = isConstantcase( 'beep' );
// returns false

bool = isConstantcase( '' );
// returns true

bool = isConstantcase( null );
// returns false