C＃如何创建用于验证值在代码列表中的单元测试？

Question

I have an app which receives data, validates it, if no errors are found it saves to the database and if errors are found they get reported but nothing gets to the database.

For example I have the following:

CREATE TABLE dimension
(
    dimension_code VARCHAR(10) NOT NULL PRIMARY KEY
);

CREATE TABLE fact_table
(
    fact_id        INT IDENTITY(1,1) NOT NULL,
    dimension_code VARCHAR(10)       NOT NULL,
    CONSTRAINT FK_fact_table 
        FOREIGN KEY (dimension_code) 
        REFERENCES dimension (dimension_code)
);

INSERT INTO dimension VALUES ('A');
INSERT INTO dimension VALUES ('B');

My app allows a user to add a value to fact_table. The code (yet to be coded) is supposed to validate that the value the user is trying to add is actually in the dimension table. If not it will give a nice spelled out error. If it is then it inserts to the database and a success message is returned.

I am starting with Test Driven Development, so I thought of 2 unit tests:

1. If the value submitted is in the code list, no errors are reported.
2. If the value submitted is not in the code list, an error is reported.

I have the classes Dimension and Fact. The Dimension class is an Entity Framework class, to check the database values. Fact has a validate method which will have many validations including the one about to be written to check against the values in the dimension table. There is also a list of errors in the app (Error is a class).

I started my first unit test, to create an error if the value is not in the dimension table. But as I understand it, a unit test should not read from the database. So what should I do, do I create a fake list of values and compare it against that? If so, what is the purpose of the test, it will always pass because I am creating the list and the value, so the list would have A,B,C and the value would be D, because I hard coded it into the test. Or should I read from the database? Or will my unit test create a Fact instance, assign it an invalid value. Call validate on it. And Assert the error list count is now 1 larger than before? But this would read from the database, and my "invalid" value could become valid in the future, the test would fail but my code would still be ok. Am I not seeing things in the correct perspective?

Answer 1

Start with creation of the interface of your app. What would you like to have? I think it should be some AddFactValue(Fact fact) method? Then you write a tests which will check what will happen with database in case you run this method with different values. In this process you will find out if you have made something wrong and so on.

Then, I suppose, you want to add your validator. Create interface for it and inject it through constructor. It will allow you to write tests for validator only. So you do the same as with AddFactValue(...) . And so on...