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Overview

NuGet.Services.Testing.Entities is a small, focused test-support library that solves a specific pain point: Entity Framework 6’s IDbSet<T> and async LINQ operators (ToListAsync, FirstOrDefaultAsync, etc.) cannot be faked with a plain in-memory list out of the box. EF’s async extension methods require the underlying IQueryProvider to implement IDbAsyncQueryProvider, which a standard List<T> does not satisfy. This library ships three building blocks that wire everything up correctly via Moq, and a high-level convenience extension that configures an entire IValidationEntitiesContext mock in one call.
This project is a test infrastructure library only — it must never be referenced from production code. It targets net472 and is intended for use inside xUnit / MSTest unit test projects within the NuGetGallery solution.

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Role in the System

The NuGetGallery solution separates package validation concerns into NuGet.Services.Validation, which defines the EF entity model (IValidationEntitiesContext, PackageValidation, PackageValidationSet, certificate chain entities, etc.). Every service that queries that context needs a way to write fast, isolated unit tests without a real SQL Server connection. NuGet.Services.Testing.Entities sits between those two concerns: 
Production code                    Test code
──────────────────                 ────────────────────────────────
NuGet.Services.Validation          NuGet.Services.Testing.Entities
  IValidationEntitiesContext   <─────  IValidationEntitiesContextExtensions
  IDbSet<PackageValidation>    <─────  IDbSetMockExtensions
  (async LINQ queries)         <─────  TestDbAsyncQueryProvider / Enumerator
Any test project that validates business logic against the EF validation context can reference this library instead of duplicating the async-mock boilerplate.

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Key Files and Classes

FileClass / TypePurpose
TestDbAsyncQueryProvider.csTestDbAsyncQueryProvider<TEntity>Implements IDbAsyncQueryProvider by wrapping a real IQueryProvider; satisfies EF’s requirement for async LINQ (ToListAsync, etc.) in tests
TestDbAsyncQueryProvider.csTestDbAsyncEnumerable<T>Extends EnumerableQuery<T> and implements IDbAsyncEnumerable<T>; acts as the async-iterable wrapper around an in-memory sequence
TestDbAsyncQueryProvider.csTestDbAsyncEnumerator<T>Adapts a synchronous IEnumerator<T> to IDbAsyncEnumerator<T> by returning Task.FromResult from MoveNextAsync
IDbSetMockExtensions.csIDbSetMockExtensions (static)Extension methods on Mock<TDbSet> and Mock<TContext> that configure all IQueryable, async-enumerable, Add, and Remove mock behaviors against a given in-memory collection
IValidationEntitiesContextExtensions.csIValidationEntitiesContextExtensions (static)Single Mock() extension on Mock<IValidationEntitiesContext> that bulk-configures all 11 IDbSet properties of the validation context in one call

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Dependencies

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NuGet Package References

PackageRole
MoqMocking framework used to create Mock<IDbSet<T>> and Mock<IValidationEntitiesContext> instances; version is inherited from the solution-level Directory.Packages.props

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Internal Project References

ProjectRole
NuGet.Services.ValidationProvides IValidationEntitiesContext and all entity types (PackageValidation, PackageValidationSet, ValidatorStatus, PackageSigningState, PackageSignature, TrustedTimestamp, EndCertificate, EndCertificateValidation, PackageRevalidation, ParentCertificate, CertificateChainLink) that the mock extensions are typed against
There is no direct reference to the EntityFramework NuGet package. The library relies only on the System.Data.Entity and System.Data.Entity.Infrastructure namespaces that are available via the .NET Framework 4.7.2 target and the EF6 assemblies pulled in transitively by NuGet.Services.Validation.

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Usage Pattern

Quick context mock

Call .Mock(...) with only the entity collections you care about. All other IDbSet properties are still configured as empty sets, so queries against them do not throw.
var ctx = new Mock<IValidationEntitiesContext>();
ctx.Mock(
    packageValidations: new List<PackageValidation>
    {
        new PackageValidation { Key = 1 }
    });

// Async LINQ works correctly
var result = await ctx.Object.PackageValidations
    .Where(v => v.Key == 1)
    .ToListAsync();

Generic DbSet mock

Use SetupDbSet directly when working with custom IDbSet types outside the validation context.
var dbSetMock = new Mock<IDbSet<MyEntity>>();
dbSetMock.SetupDbSet(new[] { new MyEntity() });

// Add / Remove callbacks are wired too
dbSetMock.Object.Add(new MyEntity());

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Notable Patterns and Implementation Details

Async shim pattern — TestDbAsyncQueryProvider and TestDbAsyncEnumerator are a direct adaptation of the Microsoft MSDN guidance for testing EF6 async queries. The source comment in TestDbAsyncQueryProvider.cs acknowledges this origin explicitly. The approach wraps synchronous in-memory LINQ with Task.FromResult(...) calls, which is safe in unit tests because there is no real I/O.
Mutable in-memory collection — IDbSetMockExtensions.SetupDbSet captures the seed data as an IQueryable<TEntity> local variable and re-assigns it inside the Add and Remove Moq callbacks using Concat / Where. This means the mock DbSet supports mutations during a test, but the mutations are not thread-safe and the collection reference is rebuilt on every add/remove.
EF6 only — not compatible with EF Core — SetupDbSet requires TDbSet : IDbSet<TEntity>. EF Core uses DbSet<T> directly and does not implement IDbSet<T>, so this library cannot be used with EF Core contexts. It is strictly an EF 6 / net472 utility.
Namespace placement — IDbSetMockExtensions is declared in the System.Data.Entity namespace (not NuGet.Services.Testing.Entities), so consuming test projects pick up the extension methods automatically whenever they have a using System.Data.Entity; directive — no extra using statement is required.

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File Inventory

FileLinesDescription
NuGet.Services.Testing.Entities.csproj17Project file; targets net472, references Moq and NuGet.Services.Validation
README.md21Brief description and usage example
TestDbAsyncQueryProvider.cs109Core async shim: TestDbAsyncQueryProvider<T>, TestDbAsyncEnumerable<T>, TestDbAsyncEnumerator<T>
IDbSetMockExtensions.cs64Generic SetupDbSet extensions for any Mock<IDbSet<TEntity>>
IValidationEntitiesContextExtensions.cs50Validation-context-specific Mock() convenience extension wiring all 11 entity sets