public void Validate_WhenCalled_AssertShouldBeUnknownValueWasCalledOnObjectValidatorWithAccountNumber()
        {
            string accountNumber            = _fixture.Create <string>().ToUpper();
            ICreateBudgetAccountCommand sut = CreateSut(accountNumber);

            sut.Validate(_validatorMockContext.ValidatorMock.Object, _accountingRepositoryMock.Object, _commonRepositoryMock.Object);

            _validatorMockContext.ObjectValidatorMock.Verify(m => m.ShouldBeUnknownValue(
                                                                 It.Is <string>(value => string.CompareOrdinal(value, accountNumber) == 0),
                                                                 It.IsNotNull <Func <string, Task <bool> > >(),
                                                                 It.Is <Type>(type => type == sut.GetType()),
                                                                 It.Is <string>(field => string.CompareOrdinal(field, "AccountNumber") == 0),
                                                                 It.Is <bool>(allowNull => allowNull == false)),
                                                             Times.Once);
        }