如何模拟 NpgsqlTransaction 和 NpgsqlConnection？

Question

I am currently trying to write unittest for method such as this

    public bool SaveSchema(Schema newSchema, NpgsqlTransaction transaction)

and the properties being parsed the method is a Schema, and a NpgsqlTransaction transaction. The schema can easily be generated, as it code I have full access to but the transaction is a bit of a different story.

I cannot seem to figure out a good way of mocking this?

I tried writing wrapper for it, but NpgsqlTransaction don't have a public constructor, so it is not possible to make one, or I end up writing the entire thing twice

here is my attempt - isn't there no better way of mocking the NpgsqlTransaction?

   public class NpgsqlConnectionAdapter : INpgsqlConnectionAdapter
    {
        private readonly NpgsqlConnection npgsqlConnection;

        public NpgsqlConnectionAdapter()
        {
            npgsqlConnection = new();
        }

        public NpgsqlTransaction BeginTransaction()
        {
            return npgsqlConnection.BeginTransaction();
        }

        public void Commit()
        {

        }

    }

    public class NpgsqlTransactionAdapter : INpgsqlTransactionAdapter
    {

        private readonly NpgsqlTransaction npgsqlTransaction;

        public void Commit()
        {
            npgsqlTransaction.Commit();
        }

    }

    public interface INpgsqlConnectionAdapter
    {

    }

    public interface INpgsqlTransactionAdapter
    {

    }

Answer 1

Mocking your database is a huge effort and probably worthless in the end. You will find that you spent more time on mocking extremely complicated things and you gain nothing, because you still don't know if your actual statements would really work on a real database.

The way to go here is to write your database layer as technology agnostic as possible. For example, you should use IDbConnection and IDbTransaction in your code and only have single point where you actually decide that it's a NpgsqlConnection with a specific connection string in production.

That way for your unit tests you only need to change a single line, and tell it to (for example) use an Sqlite in-memory database instead. Now you can unit test with a real database, but one that is self-contained to this test only.