public function testTooltip()
{
$tooltip = new Tooltip(['formatter' => new JsExpression('function(){ return \'<b>\' + this.series.name + \'</b><br/>\' + this.x + \': +\' + this.y; }')]);
$this->assertEquals('{"formatter":function(){ return \'<b>\' + this.series.name + \'</b><br/>\' + this.x + \': +\' + this.y; }}', $tooltip->toJson());
$tooltip = new Tooltip();
$tooltip->setPointFormat('{series.name}: <b>{point.y}</b><br/>');
$tooltip->setValueSuffix(' cm');
$tooltip->setShared(true);
$this->assertEquals('{"pointFormat":"{series.name}: <b>{point.y}</b><br/>","valueSuffix":" cm","shared":true}', $tooltip->toJson());
}