[Fact]
public void FunctionalTest()
{
    // arrange
    var expectedCustomer = new Customer("fist@sea.com");
    var expectedReportBody = "the report body";

    Func<IEnumerable<Customer>> getCustomersForCustomerReport  = 
        () => new[] {expectedCustomer};

    Func<Customer, Report> createCustomerReport = 
        customer => new Report(expectedCustomer.Email, expectedReportBody);

    var actualToAddress = "";
    var actualBody = "";

    Action<string, string> sendEmail = (toAddress, body) =>
    {
        actualToAddress = toAddress;
        actualBody = body;
    };

    // act
    Functional.RunCustomerReportBatch(getCustomersForCustomerReport, createCustomerReport, sendEmail);

    // assert
    Assert.Equal(expectedCustomer.Email, actualToAddress);
    Assert.Equal(expectedReportBody, actualBody);
}