AutoFixtureParameterSource.cs

            ...
            if (allEntitiesAttribute != null)
            {
                var dbContext = new MyDbContext();

                return ((IObjectContextAdapter)dbContext)
                 .ObjectContext
                 .MetadataWorkspace
                 .GetItems<EntityType>(DataSpace.OSpace)
                 .Select(e => Type.GetType(e.FullName))
                 .Except(allEntitiesAttribute.Except)
                 .Select(entityType => new[] { specimenContext.Resolve(entityType) })
                 .ToArray();
            }
            ...