Unit testing a sql string

I am putting in unit tests for a brown field win forms app. I have complete freedom of choice on what kinda unit test framework I have

The problem I have is there is masses of SQL string statement in the code. Think something like this

SELECT *
FROM Sale 
INNER JOIN SaleItem ON Sale.ID = SaleItem.SaleID
WHERE ID = 5

I want to run this sql agenst some object or a thing, that is NOT a DB and get a item.
It has to be smart enough to actually filter So it the Sale object was like the following table, it would only return the one with the ID 5.

ID DateDispatched CustomerID
1  1/1/1          5   
2  2/2/2          6   
5  3/3/3          7 

I have thought of running sql command on datasets and XML, and relised that wont work. I guess LINQ has spoiled me over that last few years cus I cant work out how to do this. And im afraid there is so much logic building up massive SQL statement, I have to put some tests on them.

Would be more than willing to hear about other options like moving the SQL to stored procedure in the DB, if you can recommend a good unit testing framework.

Now I don't like SQL being built in the app and would love to change it to entity framework, but its a 10 year old application and that's just not a option.