Microsoft.Testing.Extensions.Hosting

Microsoft.Testing.Extensions.Hosting

Microsoft.Testing.Extensions.Hosting runs Microsoft.Testing.Platform inside an application-owned Microsoft.Extensions.Hosting host.

The host remains the composition root and owns its service provider, configuration, logging, OpenTelemetry providers, lifetime, and disposal. The extension starts and stops the host around the test run but never disposes it.

Install the package

dotnet add package Microsoft.Testing.Extensions.Hosting
dotnet add package Microsoft.Extensions.Hosting
dotnet add package MSTest

Generated entry point

MSTest.Sdk and other MTP projects can generate the hosting glue instead of maintaining a custom Program.cs:

<PropertyGroup>
  <TestingPlatformHostFactory>Contoso.Tests.TestHost.CreateHost</TestingPlatformHostFactory>
  <TestingPlatformOpenTelemetryMode>HostOwned</TestingPlatformOpenTelemetryMode>
</PropertyGroup>

The configured method has this V1 contract:

public static Task<IHost> CreateHost();

It returns one fresh, unstarted host. It does not receive MTP command-line arguments. Generated code owns and disposes the host (preferring IAsyncDisposable when implemented), invokes the existing RunTestingPlatformAsync bridge, and preserves the generated AddSelfRegisteredExtensions(builder, args) registration exactly once. Help and info options supplied on the process command line or through response files do not invoke the factory.

TestingPlatformOpenTelemetryMode=HostOwned requires Microsoft.Testing.Extensions.OpenTelemetry. It activates only the MTP diagnostics producer; the host remains the sole owner of providers, exporters, resource identity, and disposal.

The factory must configure a host that never writes startup, shutdown, logging, or exporter output to standard output. MTP reserves stdout for machine-readable modes such as --list-tests json, server JSON-RPC, and the dotnet test protocol. Remove default console logging providers and use OTLP, files, or another non-stdout sink.

Help or info activated only through configuration is resolved while the MTP application is built, after the factory-created host supplies its configuration snapshot. In that uncommon case the factory is invoked, but the host contract still requires construction to be side-effect-free until StartAsync.

Manual usage

using System.Reflection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Microsoft.Testing.Extensions;

HostApplicationBuilder builder = Host.CreateApplicationBuilder();
builder.Logging.ClearProviders();

using IHost host = builder.Build();
return await host.RunTestingPlatformAsync(args, testApplication =>
{
    testApplication.AddMSTest(() => [Assembly.GetExecutingAssembly()]);
});

The process command line belongs to MTP in this composition. Configure the host through code, environment variables, or application configuration rather than passing the same argument array to both parsers.

RunTestingPlatformAsync:

1. Creates an MTP application builder.
2. Imports a read-only snapshot of the host's IConfiguration.
3. Forwards MTP diagnostic logs to the host-owned ILoggerFactory.
4. Applies each caller-owned ITestingPlatformBuilderConfigurator registered in the host service provider.
5. Invokes the caller's MTP registration callback, which therefore has final configuration precedence.
6. Starts the host before building MTP, so host-owned observability providers can subscribe first.
7. Links the caller token and IHostApplicationLifetime.ApplicationStopping to MTP's cooperative cancellation path.
8. Runs MTP and returns its exit code.
9. Stops the host in a finally block.

Ownership and limitations

• The caller owns and disposes the IHost.
• Builder configurators are borrowed from host.Services; the Hosting extension never disposes them separately.
• The extension does not create a second Microsoft.Extensions dependency-injection container.
• Imported configuration has snapshot semantics and does not propagate reloads after the MTP application is built.
• Composition is process-local. Live services do not cross into separately launched test host or controller processes.
• Process-restart extensions (for example retry, crash dump, or hang dump scenarios) execute the generated entry point in each process. Until MTP exposes a role-aware pre-build hook, the factory can therefore be invoked in both the controller and child process; factories used with those extensions must avoid exclusive global resources such as fixed ports.
• The cancellation token controls host startup and active MTP execution. Cancellation during StartAsync follows the host contract and can throw OperationCanceledException; once MTP is running, cancellation uses MTP's cooperative path and returns the test-session-aborted exit code (3) after cleanup.
• When the host provides IHostApplicationLifetime, ApplicationStopping is linked to the same MTP cancellation source. Caller cancellation, host stopping, Ctrl+C, --timeout, controller cancellation, and test framework stop policies are peer signals; the first signal starts the same idempotent MTP shutdown path. MTP cancellation does not call StopApplication; the helper stops the host after MTP cleanup completes.
• In controller mode, cancellation uses MTP's existing controller control channel to request cooperative cancellation in the active test host process. Existing bounded termination remains the fallback for a non-cooperative child.
• Cancellation registrations are removed when execution completes. The lifetime bridge disconnects before the helper's own StopAsync, and shutdown uses an uncancelled token so graceful cleanup is still attempted without re-entering MTP cancellation.
• Exceptions from host startup, MTP construction/execution, and host shutdown are surfaced to the caller. When an operation and its cleanup both fail, the operation remains the primary exception and the cleanup exception is attached to its Data dictionary. If that dictionary cannot be updated, an AggregateException exposes the operation exception first and the cleanup exception second.

See the runnable ASP.NET Core and Aspire ServiceDefaults samples under samples/public/MTPHostIntegration.

Documentation

For comprehensive documentation, see https://aka.ms/testingplatform.

Feedback & contributing

Microsoft.Testing.Platform is an open source project. Provide feedback or report issues in the microsoft/testfx GitHub repository.