Test Durable activity dispatch

TestOrchestrationContext supports a focused unit-test boundary for .NET isolated Durable orchestrators: it records and dispatches CallActivityAsync calls. Use it when orchestration logic primarily chooses an activity name, input, options, and expected result type.

Dispatch to a real activity

Provide an async handler that maps recorded calls to real activity instances or explicit test results:

[Fact]
public async Task Orchestrator_dispatches_to_real_activity_and_records_call()
{
    var activity = new GreetingActivity("Hello");
    var context = new TestOrchestrationContext(async call =>
    {
        Assert.Equal(nameof(GreetingActivity), call.ActivityName);
        Assert.Equal(typeof(string), call.ResultType);
        return await activity.RunAsync(Assert.IsType<string>(call.Input));
    });

    var result = await GreetingOrchestrator.RunAsync(context);

    Assert.Equal("Hello, Ada!", result);
    var call = Assert.Single(context.ActivityCalls);
    Assert.Equal(nameof(GreetingActivity), call.ActivityName);
    Assert.Equal("Ada", call.Input);
    Assert.Null(call.Options);
}

ActivityCalls preserves scheduling order and exposes the task name, input, result type, and options. The handler must return a value compatible with the generic result type; null for a non-nullable value type and incompatible results fail with InvalidOperationException.

Supported and unsupported behavior

Only CallActivityAsync is emulated. Runtime-dependent context members fail explicitly:

[Fact]
public void Runtime_dependent_members_are_not_supported()
{
    var context = new TestOrchestrationContext(_ => Task.FromResult<object?>(null));

    Assert.Throws<NotSupportedException>(() => _ = context.InstanceId);
    Assert.Throws<NotSupportedException>(() => context.GetInput<string>());
    Assert.Throws<NotSupportedException>(() => context.NewGuid());
}

The test context does not emulate:

  • Durable history or deterministic replay.
  • Timers or orchestration time.
  • External events.
  • Sub-orchestrators or child-instance lifecycle.
  • Entity calls, suspension, termination, purge, or instance management.
  • Runtime-generated instance IDs or deterministic GUIDs.

Those behaviors require the real Durable runtime or a dedicated runtime-level harness. Do not use this helper to claim replay safety or production scheduling correctness.

Troubleshooting dispatch

  • An unexpected activity should make the handler throw with the recorded activity name.
  • A null result for a value type or a mismatched result type produces an explicit dispatch error.
  • If orchestrator code reads runtime-dependent members, NotSupportedException identifies that the scenario has crossed this helper's boundary.

See DurableFunctionTests for handler validation and result-type failure coverage.

See the Azure Functions API reference for TestOrchestrationContext and RecordedActivityCall.

Edit this page