Unable to mock Table object returned from IDynamoDBContext.GetTargetTable

[IIFE]

Unable to mock Table object returned from IDynamoDBContext.GetTargetTable

I am injecting IDynamoDBContext in a constructor, and then calling GetTargetTable to get the Table object representing the table for an entity. I then use that Table object to carry out some operations on DynamoDB, or to extract metadata about the table (i.e table name, hash key name, etc).

The problem is I cannot find a way to mock the return value of GetTargetTable as the Table class doesn't appear to be mockable.

Expected Behavior

I would expect GetTargetTable to return an interface that defines the operations which can be carried out on an entity's table, rather than the concrete Table implementation.

Current Behavior

GetTargetTable returns concrete class rather than an abstraction (i.e interface)

Possible Solution

Create an interface abstract over the Table class and have GetTargetTabke return the interface.

Steps to Reproduce (for bugs)

Following class shows an example of the issue:

public class EntityBase
{
	public string Id { get; set; }
}
	
public class DynamoDBRepository<TEntity>
	where TEntity : EntityBase
{
	private IDynamoDBContext DbContext { get; }

	private Table Table { get; }

	private ITableMetadata TableMetadata { get; }

	public DynamoDBRepository(IDynamoDBContext dbContext)
	{			
		DbContext = dbContext ?? throw new ArgumentNullException(nameof(dbContext));
			
		Table = DbContext.GetTargetTable<TEntity>()
			?? throw new InvalidOperationException($"Unable to retrieve table information for {typeof(TEntity).FullName} from {nameof(IDynamoDBContext)}");

		TableMetadata = new TableMetadata(Table.TableName, Table.HashKeys?.FirstOrDefault(), Table.RangeKeys?.FirstOrDefault());
	}

	public async Task UpdateAsync(TEntity entity)
	{			
		ExpectedState state = new ExpectedState();
		state.AddExpected(TableMetadata.IdName, ScanOperator.Equal, entity.Id);

                // Cannot mock this.
		await Table.UpdateItemAsync(DbContext.ToDocument(entity), new UpdateItemOperationConfig{ ExpectedState = state});
	}
}

Context

Unable to unit tests services that consume IDynamoDBContext and rely on the instance returned by GetTargetTable to carry out certain operations.

Your Environment

• AWSSDK.Core version used: 2.1

[klaytaybai]

Thanks for the feedback.

[mbp]

Basically the same as #632 which is added to feature request backlog 2.5 years ago. Wouldn't count on it to happen...

[klaytaybai]

We do have some other issues around this topic too, but it is unlikely to happen until a next major version.

[kwbauer]

Or add a public parameterless constructor. That way mocking frameworks can construct the object and we can mock the properties and methods we need to.

The main problem is that most of these objects have no public constructors at all. Sure, they aren't needed for the library but it makes our code which uses your library not testable.

Adding the public constructors is a good compromise that is fairly easy to do for a minor revision as it is not a breaking change.

[nicollaas94]

Is there a feature-request list where we can vote on this one?
creating wrappers for testing our services is becoming annoying and far from ideal

[AdamLewisGMSL]

Adding my voice to this. Currently have a whole tranche of code I can't test because I can't mock the types in the DynamoDb package. This is one of them.

[Darren-Kelly]

I also just ran into the same issue when trying to add unit tests. I cannot mock the Table class.

[brenocg1]

Hello,

Any update regarding this?

[dcorrea777]

I also have the same problem, I can't seem to mock some classes to do my unit tests.

The problem is that the maintainers say: "we accept PRS" but there are several open PRs that are even more than a year old.

[96malhar]

Hello, we have been working on the V4 of the AWS SDK for .NET. We have added the ability to mock various DynamoDB operations by adding interfaces in both the Data Model mode and Document Model mode in DynamoDB.

Refer to this PR - #3450

Specifically for the IDynamoDBContext.GetTargetTable methods, it now returns an ITable interface which is implemented the by the Table class. The interface can be mocked to simulate table operations in unit tests.

This feature is available in the AWSSDK.DynamoDBv2 Version 4.0.0-preview.2

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