public void TestCalculateCharge()
{
// Arrange
Client person; //declare reference variable
string name = "Fred";
int acctNo = 1;
string type = "r";
decimal kwh = 5;
decimal expectedCharge = 6.26m;
decimal actualCharge;
//Act
person = new Residential(name, acctNo, type); // create account with initial balance
actualCharge = person.CalculateBill(kwh);
//Assert
Assert.AreEqual(expectedCharge, actualCharge);
}