NBuilder and DbContext invalid cast issue - nunit

Question

I am really new to NBuilder, but it looks awesome so I thought I would have a go.
I have a DatabaseContext which just inherits from DbContext like this:
public class DatabaseContext : DbContext
Now, I have created a service that queries the DatabaseContext like this:
public async Task<List<Strategy>> Handle(StrategyList query, CancellationToken cancellationToken)
{
return _databaseContext.Strategies.ToList();
}
And now I want to make a test.
I set this Context up like this:
public class StrategyListContext
{
public readonly DatabaseContext DatabaseContext;
private StrategyListContext()
{
DatabaseContext = CreateDatabaseContext();
}
private DatabaseContext CreateDatabaseContext()
{
var dbContext = Substitute.For<DatabaseContext>();
var items = Builder<Strategy>.CreateListOfSize(10).Build();
dbContext.Strategies.ToList().Returns(items);
return dbContext;
}
public static StrategyListContext GivenServices() => new StrategyListContext();
public StrategyListHandler WhenCreateHandler() => new StrategyListHandler(DatabaseContext);
}
The most important part is the CreateDatabaseContext method.
It is like this:
private DatabaseContext CreateDatabaseContext()
{
var dbContext = Substitute.For<DatabaseContext>();
var items = Builder<Strategy>.CreateListOfSize(10).Build();
dbContext.Strategies.ToList().Returns(items);
return dbContext;
}
But when I run the test, I get this error:
System.InvalidCastException : Unable to cast object of type 'Castle.Proxies.ObjectProxy' to type 'Microsoft.EntityFrameworkCore.Metadata.Internal.Model'.
Does anyone know what I can do to get this working?
So I found this question:
How do I mock DbContext using NSubstitute and then add/remove data
And I have changed my method to this:
private DatabaseContext CreateDatabaseContext()
{
var dbContext = Substitute.For<DatabaseContext>();
var items = Builder<Strategy>.CreateListOfSize(10).Build().AsQueryable();
var dbSet = Substitute.For<DbSet<Strategy>, IQueryable<Strategy>>();
((IQueryable<Strategy>)dbSet).Provider.Returns(items.Provider);
((IQueryable<Strategy>)dbSet).Expression.Returns(items.Expression);
((IQueryable<Strategy>)dbSet).ElementType.Returns(items.ElementType);
((IQueryable<Strategy>)dbSet).GetEnumerator().Returns(items.GetEnumerator());
dbContext.Set<Strategy>().Returns(dbSet);
return dbContext;
}
But I still get the same error....

Answer 1

The second solution was soooo close, it was simply this:
private static DatabaseContext CreateDatabaseContext()
{
var dbContext = Substitute.For<DatabaseContext>();
var items = Builder<Hall>.CreateListOfSize(10).Build().AsQueryable();
var dbSet = Substitute.For<DbSet<Hall>, IQueryable<Hall>>();
((IQueryable<Hall>)dbSet).Provider.Returns(items.Provider);
((IQueryable<Hall>)dbSet).Expression.Returns(items.Expression);
((IQueryable<Hall>)dbSet).ElementType.Returns(items.ElementType);
((IQueryable<Hall>)dbSet).GetEnumerator().Returns(items.GetEnumerator());
dbContext.Halls = dbSet;
return dbContext;
}
NB: the line that states: dbContext.Halls = dbSet instead of dbContext.Set<Strategy>().Returns(dbSet);