MockAsyncEnumerable 3.0.0.3872

A simple implementation for transforming synchronous collections into async enumerables, enabling seamless testing of EF Core queries, paginated grids, and LINQ operations, or any action or dynamic aggregated query using EF Core (Microsoft.EntityFrameworkCore) through Expressions (System.Linq.Expressions) with IAsyncEnumerable<T>.

This library was born from the necessity to implement paged grid results in projects where data was provided by stored procedures or in-memory collections, while still needing to support async EF Core APIs like ToListAsync(), FirstOrDefaultAsync(), etc.

Root namespace: RzR.Extensions.EntityMock (with sub-namespaces .Abstractions, .Extensions, .Faults, .Helpers).

Features

• Convert IEnumerable<T>, IQueryable<T>, and arrays to IAsyncEnumerable<T> / IQueryable<T>;
• Public APIs return the IMockAsyncEnumerable<T> abstraction (combines IAsyncEnumerable<T> + IQueryable<T>);
• Builder pattern for fluent async enumerable construction;
• Factory methods for quick creation (Empty, Single, Create);
• Fault injection on the builder: artificial latency, throw-at-index, and time-based cancellation — useful for testing retry, timeout and cancellation logic;
• Full support for LINQ async operations (Where, Select, OrderBy, etc.);
• Comprehensive null guards and error handling;
• Proper cancellation token support (linked tokens for combined caller / internal cancellation);
• Optimized disposal patterns (IAsyncDisposable);
• Multi-target: netstandard2.0, netstandard2.1, net5.0–net9.0.

Installation

In case you wish to use it in your project, u can install the package from <a href="https://www.nuget.org/packages/MockAsyncEnumerable" target="_blank">nuget.org</a> or specify what version you want:

Install-Package MockAsyncEnumerable

Or specify a version:

Install-Package MockAsyncEnumerable -Version x.x.x.x

Examples

Using Extension Methods

using RzR.Extensions.EntityMock.Extensions;
using Microsoft.EntityFrameworkCore;

// Convert a list to async enumerable
var users = new List<User>
{
    new User { Id = 1, Name = "Alice" },
    new User { Id = 2, Name = "Bob" }
};

var asyncUsers = users.ToMockAsyncEnumerable();
var result = await asyncUsers.Where(u => u.Id > 1).ToListAsync();

Using Factory Methods

using RzR.Extensions.EntityMock;
using Microsoft.EntityFrameworkCore;

// Create empty async enumerable
var empty = AsyncEnumerableFactory.Empty<User>();

// Create from single item
var single = AsyncEnumerableFactory.Single(new User { Id = 1, Name = "Alice" });

// Create from multiple items
var multiple = AsyncEnumerableFactory.Create(
    new User { Id = 1, Name = "Alice" },
    new User { Id = 2, Name = "Bob" }
);

var users = await multiple.ToListAsync();

Using Builder Pattern

using RzR.Extensions.EntityMock;
using Microsoft.EntityFrameworkCore;

// Build an async enumerable fluently
var users = AsyncEnumerableFactory.Builder<User>()
    .Add(new User { Id = 1, Name = "Alice" })
    .Add(new User { Id = 2, Name = "Bob" })
    .AddRange(moreUsers)
    .Build();

var result = await users.ToListAsync();

Fault Injection (latency, exceptions, cancellation)

The builder can inject realistic failure modes so tests can exercise retry, timeout and cancellation paths in production code without changing it:

using RzR.Extensions.EntityMock;
using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore;

var slow = AsyncEnumerableFactory.Builder<User>()
    .AddRange(users)
    .WithDelay(TimeSpan.FromMilliseconds(50)) // per-item latency
    .ThrowAfter(3, _ => new DbUpdateException("forced")) // throw at index 3
    .CancelAfter(TimeSpan.FromSeconds(1)) // internal cancel
    .Build();

// Caller-supplied cancellation token is honored alongside the internal one.
await foreach (var u in slow.WithCancellation(ct)) { /* ... */ }

Available builder fault APIs:

Using EnumerableInvoker (deprecated)

!!! EnumerableInvoker is marked [Obsolete] and will be removed in the next major version. Prefer AsyncEnumerableFactory, the ToMockAsyncEnumerable() extension methods, or AsyncEnumerableBuilder<T>.

using RzR.Extensions.EntityMock;
using Microsoft.EntityFrameworkCore;

var data = new List<User>
{
    new User { Id = 1, Name = "Alice" },
    new User { Id = 2, Name = "Bob" }
};

#pragma warning disable CS0618
var asyncEnumerable = EnumerableInvoker.Invoke(data);
#pragma warning restore CS0618

var result = await asyncEnumerable.FirstOrDefaultAsync(u => u.Name == "Alice");

API Reference

All factory / builder / extension methods now return IMockAsyncEnumerable<T> (defined in RzR.Extensions.EntityMock.Abstractions), which extends both IAsyncEnumerable<T> and IQueryable<T>.

Abstraction (RzR.Extensions.EntityMock.Abstractions)

Extension Methods (RzR.Extensions.EntityMock.Extensions)

Factory Methods (AsyncEnumerableFactory)

Builder Pattern (AsyncEnumerableBuilder<T>)

Classic Approach (EnumerableInvoker) — deprecated