public class ApproveInvoiceTests {
    private Invoice _invoice;
    private CommandResult _result;

    public ApproveInvoiceTests(TestContext context) {
        var invoice = new Invoice("John Doe", 30m);

        context.Save(invoice);

        var message = new ApproveInvoice(invoice.Id);

        _result = context.Send(invoice);

        _invoice = context.Reload(invoice);
    }

    public void ShouldApproveInvoice() {
        _invoice.Status.ShouldEqual(InvoiceStatus.Approved);
    }

    public void ShouldRaiseApprovedEvent() {
        _result.Events.OfType<InvoiceApproved>().Count().ShouldEqual(1);
    }
}