@Test
public void testAddCustomer() {

    testBusiness.addCustomerToPhoneBook(sarah);
    int numEmployees = testBusiness.customerPhoneBook.size();
    assertEquals(1, numEmployees);
    testBusiness.addCustomerToPhoneBook(joe);
    testBusiness.addCustomerToPhoneBook(alma);
    testBusiness.addCustomerToPhoneBook(hannah);
    numEmployees = testBusiness.customerPhoneBook.size();
    assertEquals(4, numEmployees);
    testBusiness.addCustomerToPhoneBook(null);
    numEmployees = testBusiness.customerPhoneBook.size();
    assertEquals(4, numEmployees);
    testBusiness.addCustomerToPhoneBook(customerNoLastName);
    numEmployees = testBusiness.customerPhoneBook.size();
    assertEquals(4, numEmployees);
    testBusiness.addCustomerToPhoneBook(customerNoFirstName);
    numEmployees = testBusiness.customerPhoneBook.size();
    assertEquals(4, numEmployees);
    testBusiness.customerPhoneBook.clear();
}