public function testToOptionArray()
{
$excludedCountries = $this->model->getRestrictedCountries();
$countries = [['value' => 'US', 'lable' => 'United States'], ['value' => 'countryCode', 'lable' => 'countryName']];
$this->countryCollectionMock->expects($this->once())->method('addFieldToFilter')->with('country_id', ['nin' => $excludedCountries])->willReturnSelf();
$this->countryCollectionMock->expects($this->once())->method('loadData')->willReturnSelf();
$this->countryCollectionMock->expects($this->once())->method('toOptionArray')->willReturn($countries);
$header = ['value' => '', 'label' => new \Magento\Framework\Phrase('--Please Select--')];
array_unshift($countries, $header);
$this->assertEquals($countries, $this->model->toOptionArray());
}