AndreGoepel.Marten.Testing

Shared Testcontainers/PostgreSQL Marten integration-test fixture for the AndreGoepel .NET ecosystem — one MartenFixture, one pinned Postgres digest, instead of every repo carrying its own copy.

Why

Two sibling repos (marten-configuration, marten-identity) each carried a near-identical MartenFixture + IntegrationCollection: same PostgreSqlContainer lifecycle, same pinned image digest, same DocumentStore.For(...) / ResetAsync shape. Keeping the digest in lockstep across repos by hand is exactly the kind of thing that silently drifts. Three more host apps (finance-app, app-foundation, andregoepel-dev) have no integration fixture at all and mock IDocumentStore/IDocumentSession/IQuerySession with NSubstitute instead — andregoepel-dev even hand-built a reflection proxy just to simulate a DB outage. This package gives every consumer a real Postgres to test against instead.

Usage

Reference the package from a test project and use the fixture directly if you don't need any extra store configuration:

[CollectionDefinition(Name)]
public sealed class IntegrationCollection : ICollectionFixture<MartenFixture>
{
    public const string Name = "Integration";
}

Define this IntegrationCollection yourself in your test project rather than referencing one from this package. xunit collection fixtures are scoped per test assembly, so a collection defined here can't be shared as one physical container across multiple consuming assemblies anyway — each test project pays its own container start-up cost regardless of which assembly declares the [CollectionDefinition]. The package does still ship its own IntegrationCollection (bound to the base MartenFixture) as a working example / copy-paste starting point, not as something to reference across assembly boundaries.

[Collection(IntegrationCollection.Name)]
public sealed class MyStoreTests(MartenFixture fixture) : IAsyncLifetime
{
    private CancellationToken Ct => TestContext.Current.CancellationToken;

    public async ValueTask InitializeAsync() => await fixture.ResetAsync(Ct);

    public ValueTask DisposeAsync() => ValueTask.CompletedTask;

    [Fact]
    public async Task SaveAsync_ThenLoadAsync_RoundTrips()
    {
        await using var session = fixture.Store.LightweightSession();
        // ...
    }
}

ResetAsync wipes documents between tests without dropping the schema, so it belongs in InitializeAsync, not DisposeAsync — rebuilding the schema per test is the slow part this design avoids.

Extending the fixture

Some consumers need more than a vanilla store — marten-identity's fixture calls opts.InitializeIdentity() and resolves an ISettingsStore once the store is built; a future consumer might need projections or its own settings documents.

Design choice: inheritance with protected virtual hooks (template method), not composition via constructor-injected delegates. xunit's ICollectionFixture<T> / IClassFixture<T> construct the fixture type themselves and require a public parameterless constructor — a delegate-based composition design would have nowhere natural to receive the delegates without reintroducing a parameterless-constructor problem one layer up (a static factory, an ambient/service-locator pattern, ...). Subclassing sidesteps that entirely: the subclass's own parameterless constructor is what xunit calls, and MartenFixture exposes two protected virtual seams for it to override:

• ConfigureStore(StoreOptions options) — additional store configuration, run after the connection string is set and before AutoCreateSchemaObjects is applied. No-op by default.
• OnStoreInitializedAsync() — runs once Store is built; use it to resolve derived services (e.g. a settings store via DI) that need a live store. No-op by default.

ResetAsync is also virtual so a subclass can extend the cleanup (e.g. also clearing event data) while still calling the base document wipe.

This is why MartenFixture is public and unsealed, deviating from the ecosystem's "classes are internal sealed by default" rule — same kind of deliberate, documented exception as MartenSettingsStore in AndreGoepel.Marten.Configuration. Being an open extension point is the entire point of this type.

Example — the shape marten-identity's fixture would take on this package (not applied in this repo; migrating marten-identity itself is a follow-up):

public sealed class IdentityMartenFixture : MartenFixture
{
    public ISettingsStore SettingsStore { get; private set; } = null!;

    protected override void ConfigureStore(StoreOptions options) =>
        options.InitializeIdentity();

    protected override async ValueTask OnStoreInitializedAsync()
    {
        var services = new ServiceCollection();
        services.AddSingleton(Store);
        services.AddMartenConfiguration();
        SettingsStore = services.BuildServiceProvider().GetRequiredService<ISettingsStore>();
    }

    public override async Task ResetAsync(CancellationToken cancellationToken = default)
    {
        await base.ResetAsync(cancellationToken);
        await Store.Advanced.Clean.DeleteAllEventDataAsync(cancellationToken);
    }
}

[CollectionDefinition(Name)]
public sealed class IntegrationCollection : ICollectionFixture<IdentityMartenFixture>
{
    public const string Name = "Integration";
}

Postgres version

The pinned image digest lives in MartenFixture.PostgresImage (currently postgres:16-alpine@...). Bump it in one place to move every consumer to a new Postgres version at once — that lockstep bump is the reason this package exists instead of two hand-copied fixtures.

Requirements

Docker (or a compatible container runtime) must be available wherever tests run — locally and in CI. GitHub-hosted ubuntu-latest runners have Docker preinstalled.