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TaskUtilityTest.cls

@isTest
public class TaskUtilityTest
{
    @isTest static void testGetTaskPriority()
    {
        String priority=TaskUtility.getTaskPriority('AU');
        System.assertEquals('Normal', priority);
    }
    @isTest static void testTaskHighPriority()
    {
        String priority=TaskUtility.getTaskPriority('US');
        System.assertEquals('High', priority);
    }
    @isTest static void testTaskPriorityInvalid()
    {
         String priority=TaskUtility.getTaskPriority('idfdf');
        System.assertEquals(null, priority);
    }
}