Entity Framework unity testing challenges - mocking DbSet / EntityState

EntityFramework_UnitTesting_Challenges.cs

// class `Service`
public void Add()
{ 
  // this is the code I want to test
  var entry = await _dbContext.MyDbSetObject.AddAsync(data, cancellationToken);

  if (entry.State != EntityState.Added)
  {
    // log error & return
  }

  await _dbContext.SaveChangesAsync(cancellationToken);
}

// testing using Moq framework
[Fact]
public void add_should_not_save_changes_with_invalid_entity_state()
{
  // Setup
  var entity = new MyDbSetObject();
  var state = EntityState.Unchanged;
   
  var stateManager = new Mock<IStateManager>();
  stateManager
    .Setup(manager => manager.CreateEntityFinder(It.IsAny<MyDbSetObject>()))
    .Returns(Mock.Of<IEntityFinder>());

  // known issue on EF6 / NET6 https://github.com/dotnet/efcore/issues/27110
  var internalEntityEntry = new InternalEntityEntry(
    stateManager.Object,
    new RuntimeEntityType(
        name: "T",
        type: typeof(T),
        sharedClrType: false,
        model: null,
        baseType: null,
        discriminatorProperty: null,
        ChangeTrackingStrategy.Snapshot,
        indexerPropertyInfo: null,
        propertyBag: false),
    entity);
  
  var entry = new Mock<EntityEntry<MyDbSetObject>>(internalEntityEntry);
  entry.SetupGet(e => e.Entity)
    .Returns(entity);
  entry.Setup(entityEntry => entityEntry.State)
    .Returns(state);
  
  var dbSet = new Mock<DbSet<MyDbSetObject>>();
  dbSet
    .Setup(dbSet => dbSet.AddAsync(entity, It.IsAny<CancellationToken>()))
    .ReturnsAsync(entry.Object);
  
  var builder = new DbContextOptionsBuilder<DatabaseContext>();
  var dbContext = new Mock<DatabaseContext>(MockBehavior.Loose, builder.Options);
  dbContext
    .Setup(context => context.MyDbSetObject)
    .Returns(dbSet.Object);
  
  // ACT
  var target = new Service(dbContext.Object);
  target.Add(entity);
  
  // Assert
  dbSet.Verify(moqDbSet => moqDbSet.AddAsync(It.IsAny<MyDbSetObject>(), It.IsAny<CancellationToken>()),   
               Times.Once);
  dbContext.Verify(context => context.SaveChangesAsync(It.IsAny<CancellationToken>()), 
               Times.Never);
}