Moq and throwing a SqlException

If you need test cases for the Number or Message properties of the exception, you could use a builder (which uses reflection) like this:

using System;
using System.Data.SqlClient;  // .NetCore using Microsoft.Data.SqlClient;
using System.Linq;
using System.Reflection;

public class SqlExceptionBuilder
{
    private int errorNumber;
    private string errorMessage;

    public SqlException Build()
    {
        SqlError error = this.CreateError();
        SqlErrorCollection errorCollection = this.CreateErrorCollection(error);
        SqlException exception = this.CreateException(errorCollection);

        return exception;
    }

    public SqlExceptionBuilder WithErrorNumber(int number)
    {
        this.errorNumber = number;
        return this;
    }

    public SqlExceptionBuilder WithErrorMessage(string message)
    {
        this.errorMessage = message;
        return this;
    }

    private SqlError CreateError()
    {
        // Create instance via reflection...
        var ctors = typeof(SqlError).GetConstructors(BindingFlags.NonPublic | BindingFlags.Instance);
        var firstSqlErrorCtor = ctors.FirstOrDefault(
            ctor =>
            ctor.GetParameters().Count() == 7); // .NetCore should be 8 not 7
        SqlError error = firstSqlErrorCtor.Invoke(
            new object[] 
            { 
                this.errorNumber, 
                new byte(), 
                new byte(), 
                string.Empty, 
                string.Empty, 
                string.Empty, 
                new int() 
            //,new Exception()  // for .NetCore 
            }) as SqlError;

        return error;
    }
 
    private SqlErrorCollection CreateErrorCollection(SqlError error)
    {
        // Create instance via reflection...
        var sqlErrorCollectionCtor = typeof(SqlErrorCollection).GetConstructors(BindingFlags.NonPublic | BindingFlags.Instance)[0];
        SqlErrorCollection errorCollection = sqlErrorCollectionCtor.Invoke(new object[] { }) as SqlErrorCollection;

        // Add error...
        typeof(SqlErrorCollection).GetMethod("Add", BindingFlags.NonPublic | BindingFlags.Instance).Invoke(errorCollection, new object[] { error });

        return errorCollection;
    }

    private SqlException CreateException(SqlErrorCollection errorCollection)
    {
        // Create instance via reflection...
        var ctor = typeof(SqlException).GetConstructors(BindingFlags.NonPublic | BindingFlags.Instance)[0];
        SqlException sqlException = ctor.Invoke(
            new object[] 
            { 
                // With message and error collection...
                this.errorMessage, 
                errorCollection,
                null,
                Guid.NewGuid() 
            }) as SqlException;

        return sqlException;
    }
}

Then you could have a repository mock (for instance) throw an exception like this (this example uses the Moq library):

using Moq;

var sqlException = 
    new SqlExceptionBuilder().WithErrorNumber(50000)
        .WithErrorMessage("Database exception occured...")
        .Build();
var repoStub = new Mock<IRepository<Product>>(); // Or whatever...
repoStub.Setup(stub => stub.GetById(1))
    .Throws(sqlException);