In memory raven db helper code with addition of index to cover all docs to allow for a purge of the db between tests.

InMemoryDocumentStore

public class InMemoryDocumentStore : IDocumentStoreConnection
{
    public InMemoryDocumentStore()
    {
        Store = new EmbeddableDocumentStore()
        {
            RunInMemory = true
        };
        Store.RegisterListener(new NoStaleQueries());
        Store.Initialize();
        new RavenIndex().AddIndexes(this);


        // Required for in memory tests only!
        Store.DatabaseCommands.PutIndex("AllDocumentsById", new IndexDefinition
                                                {
                                                    Name = "AllDocumentsById",
                                                    Map =
                                                        "from doc in docs let DocId = doc[\"@metadata\"][\"@id\"] select new {DocId};"
                                                });
    }
    public DocumentStore Store { get; set; }
}

public interface IDocumentStoreConnection
{
    DocumentStore Store { get; set; }
}

public class NoStaleQueries : IDocumentQueryListener
{
    public void BeforeQueryExecuted(IDocumentQueryCustomization queryCustomization)
    {
        queryCustomization.WaitForNonStaleResults();
    }
}