title	Unit testing Durable Functions and Durable Task SDKs
description	Learn how to unit test orchestrator, activity, and client functions for Azure Durable Functions and standalone Durable Task SDKs.
author	cgillum
ms.topic	how-to
ms.date	02/19/2026
ms.author	azfuncdf
ms.service	azure-functions
ms.subservice	durable
zone_pivot_groups	azure-durable-approach

Unit testing

Unit tests verify business logic and protect against regressions. Durable orchestrations coordinate multiple activities and can grow complex quickly. Adding unit tests helps you catch errors early.

::: zone pivot="durable-functions"

With Durable Functions, you test orchestrators, activities, and client (trigger) functions by mocking the framework-provided context objects and calling your functions directly. This approach isolates your business logic from the Azure Functions runtime.

::: zone-end

::: zone pivot="durable-task-sdks"

The standalone Durable Task SDKs provide built-in test infrastructure that runs orchestrations in-memory without external dependencies. You register orchestrators and activities with a test worker, schedule orchestrations through a test client, and assert on the results. No mocking is required for C# and JavaScript. Python uses an executor-based approach with mock history events.

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Prerequisites

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C#

xUnit — test framework
Moq — mocking framework
Familiarity with the .NET isolated worker model

Python

Python unittest — test framework
unittest.mock — mocking library
Familiarity with the Python v2 programming model

JavaScript

JavaScript unit testing for Durable Functions isn't covered in this article.

::: zone-end

::: zone pivot="durable-task-sdks"

C#

xUnit — test framework
The Microsoft.DurableTask.InProcessTestHost NuGet package

Python

pytest — test framework (or unittest)
The durabletask PyPI package

JavaScript

Jest — test framework
The @microsoft/durabletask-js npm package

::: zone-end

Test orchestrator functions

Orchestrator functions coordinate activities, timers, and external events. They typically contain the most business logic and benefit the most from unit testing.

::: zone pivot="durable-functions"

Mock the orchestration context to control the return values of activity calls. Then call your orchestrator directly and verify the output.

C#

Consider this orchestrator that calls an activity three times:

[Function(nameof(HelloCitiesOrchestration))]
public static async Task<List<string>> HelloCities(
    [OrchestrationTrigger] TaskOrchestrationContext context)
{
    var outputs = new List<string>
    {
        await context.CallActivityAsync<string>(nameof(SayHello), "Tokyo"),
        await context.CallActivityAsync<string>(nameof(SayHello), "Seattle"),
        await context.CallActivityAsync<string>(nameof(SayHello), "London")
    };

    return outputs;
}

Use Moq to mock TaskOrchestrationContext and set up expected return values for each activity call:

[Fact]
public async Task HelloCities_ReturnsExpectedGreetings()
{
    var contextMock = new Mock<TaskOrchestrationContext>();

    contextMock.Setup(x => x.CallActivityAsync<string>(
        It.Is<TaskName>(n => n.Name == nameof(SayHello)),
        It.Is<string>(n => n == "Tokyo"),
        It.IsAny<TaskOptions>())).ReturnsAsync("Hello Tokyo!");

    contextMock.Setup(x => x.CallActivityAsync<string>(
        It.Is<TaskName>(n => n.Name == nameof(SayHello)),
        It.Is<string>(n => n == "Seattle"),
        It.IsAny<TaskOptions>())).ReturnsAsync("Hello Seattle!");

    contextMock.Setup(x => x.CallActivityAsync<string>(
        It.Is<TaskName>(n => n.Name == nameof(SayHello)),
        It.Is<string>(n => n == "London"),
        It.IsAny<TaskOptions>())).ReturnsAsync("Hello London!");

    var result = await HelloCitiesOrchestration.HelloCities(contextMock.Object);

    Assert.Equal(3, result.Count);
    Assert.Equal("Hello Tokyo!", result[0]);
    Assert.Equal("Hello Seattle!", result[1]);
    Assert.Equal("Hello London!", result[2]);
}

Python

Consider this orchestrator that chains three activity calls:

import azure.durable_functions as df

def my_orchestrator(context: df.DurableOrchestrationContext):
    result1 = yield context.call_activity("say_hello", "Tokyo")
    result2 = yield context.call_activity("say_hello", "Seattle")
    result3 = yield context.call_activity("say_hello", "London")
    return [result1, result2, result3]

Mock the context and use orchestrator_generator_wrapper to process the generator. This utility simulates the Durable Functions replay mechanism:

import unittest
from unittest.mock import Mock, call
from azure.durable_functions.testing import orchestrator_generator_wrapper

from function_app import my_orchestrator


def mock_activity(activity_name, input_value):
    mock_task = Mock()
    mock_task.result = f"Hello {input_value}!"
    return mock_task


class TestOrchestrator(unittest.TestCase):
    def test_chaining_orchestrator(self):
        func_call = my_orchestrator.build().get_user_function().orchestrator_function

        context = Mock()
        context.call_activity = Mock(side_effect=mock_activity)

        user_orchestrator = func_call(context)
        values = list(orchestrator_generator_wrapper(user_orchestrator))

        expected_calls = [
            call("say_hello", "Tokyo"),
            call("say_hello", "Seattle"),
            call("say_hello", "London"),
        ]
        self.assertEqual(context.call_activity.call_args_list, expected_calls)
        self.assertEqual(values[-1], ["Hello Tokyo!", "Hello Seattle!", "Hello London!"])

JavaScript

JavaScript unit testing for Durable Functions isn't covered in this article.

::: zone-end

::: zone pivot="durable-task-sdks"

C#

Use DurableTaskTestHost to run orchestrations in-memory. Register your production orchestrator and activity classes, schedule an orchestration, and assert on the result.

Given these production classes:

class HelloCitiesOrchestrator : TaskOrchestrator<string, List<string>>
{
    public override async Task<List<string>> RunAsync(
        TaskOrchestrationContext context, string input)
    {
        var outputs = new List<string>
        {
            await context.CallActivityAsync<string>(nameof(SayHelloActivity), "Tokyo"),
            await context.CallActivityAsync<string>(nameof(SayHelloActivity), "Seattle"),
            await context.CallActivityAsync<string>(nameof(SayHelloActivity), "London")
        };
        return outputs;
    }
}

class SayHelloActivity : TaskActivity<string, string>
{
    public override Task<string> RunAsync(TaskActivityContext context, string name)
    {
        return Task.FromResult($"Hello {name}!");
    }
}

[Fact]
public async Task HelloCities_ReturnsExpectedGreetings()
{
    await using var host = await DurableTaskTestHost.StartAsync(tasks =>
    {
        tasks.AddOrchestrator<HelloCitiesOrchestrator>();
        tasks.AddActivity<SayHelloActivity>();
    });

    string instanceId = await host.Client.ScheduleNewOrchestrationInstanceAsync(
        nameof(HelloCitiesOrchestrator));
    OrchestrationMetadata result = await host.Client.WaitForInstanceCompletionAsync(
        instanceId, getInputsAndOutputs: true);

    Assert.Equal(OrchestrationRuntimeStatus.Completed, result.RuntimeStatus);

    var output = result.ReadOutputAs<List<string>>();
    Assert.Equal(3, output.Count);
    Assert.Equal("Hello Tokyo!", output[0]);
    Assert.Equal("Hello Seattle!", output[1]);
    Assert.Equal("Hello London!", output[2]);
}

DurableTaskTestHost runs a complete in-memory orchestration engine. No external services or sidecar processes are required.

Python

The Python Durable Task SDK doesn't yet provide a built-in test harness like C# and JavaScript. Use standard mocking to test orchestrator logic. Mock the OrchestrationContext and drive the generator by sending simulated activity results back for each yield:

from unittest.mock import Mock, call
from durabletask import task


def hello(ctx: task.ActivityContext, name: str) -> str:
    return f"Hello {name}!"


def hello_cities(ctx: task.OrchestrationContext, _):
    result1 = yield ctx.call_activity(hello, input="Tokyo")
    result2 = yield ctx.call_activity(hello, input="Seattle")
    result3 = yield ctx.call_activity(hello, input="London")
    return [result1, result2, result3]


def test_hello_cities():
    ctx = Mock(spec=task.OrchestrationContext)

    # Each call_activity returns a mock task; collect them to send results back
    mock_tasks = []
    def fake_call_activity(activity, *, input):
        t = Mock()
        t._input = input
        mock_tasks.append(t)
        return t

    ctx.call_activity = Mock(side_effect=fake_call_activity)

    # Start the generator
    gen = hello_cities(ctx, None)
    yielded = next(gen)  # first yield: call_activity(hello, input="Tokyo")

    # Send simulated results back for each yield
    try:
        yielded = gen.send("Hello Tokyo!")
        yielded = gen.send("Hello Seattle!")
        gen.send("Hello London!")
    except StopIteration as e:
        result = e.value

    # Verify the orchestrator called the right activities
    assert ctx.call_activity.call_count == 3
    assert result == ["Hello Tokyo!", "Hello Seattle!", "Hello London!"]

This approach tests the orchestrator's control flow without depending on SDK internals.

JavaScript

Use TestOrchestrationWorker and TestOrchestrationClient to run orchestrations in-memory:

const {
    InMemoryOrchestrationBackend,
    TestOrchestrationClient,
    TestOrchestrationWorker,
    OrchestrationStatus,
} = require("@microsoft/durabletask-js");

test("helloCities returns expected greetings", async () => {
    const backend = new InMemoryOrchestrationBackend();
    const client = new TestOrchestrationClient(backend);
    const worker = new TestOrchestrationWorker(backend);

    const sayHello = async (_, name) => `Hello ${name}!`;

    const helloCities = async function* (ctx) {
        const outputs = [];
        outputs.push(yield ctx.callActivity(sayHello, "Tokyo"));
        outputs.push(yield ctx.callActivity(sayHello, "Seattle"));
        outputs.push(yield ctx.callActivity(sayHello, "London"));
        return outputs;
    };

    worker.addOrchestrator(helloCities);
    worker.addActivity(sayHello);
    await worker.start();

    const id = await client.scheduleNewOrchestration(helloCities);
    const state = await client.waitForOrchestrationCompletion(id, true, 10);

    expect(state.runtimeStatus).toEqual(OrchestrationStatus.COMPLETED);
    expect(JSON.parse(state.serializedOutput)).toEqual([
        "Hello Tokyo!",
        "Hello Seattle!",
        "Hello London!",
    ]);

    await worker.stop();
});

The test infrastructure runs the full orchestration engine in-process. No sidecar or external services are required.

::: zone-end

Test activity functions

Activity functions contain the actual work — calling APIs, processing data, or interacting with external systems. They're the simplest function type to test because they have no framework-specific replay behavior.

::: zone pivot="durable-functions"

C#

Activity functions in Azure Functions receive an input and optionally a FunctionContext. Test them like any other function:

[Function(nameof(SayHello))]
public static string SayHello(
    [ActivityTrigger] string name, FunctionContext executionContext)
{
    return $"Hello {name}!";
}

[Fact]
public void SayHello_ReturnsExpectedGreeting()
{
    var result = HelloCitiesOrchestration.SayHello("Tokyo", Mock.Of<FunctionContext>());
    Assert.Equal("Hello Tokyo!", result);
}

Python

Activity functions in Azure Functions are regular Python functions. Test them directly. For more information, see Azure Functions Python unit testing.

def say_hello(name: str) -> str:
    return f"Hello {name}!"

def test_say_hello():
    result = say_hello("Tokyo")
    assert result == "Hello Tokyo!"

JavaScript

JavaScript unit testing for Durable Functions isn't covered in this article.

::: zone-end

::: zone pivot="durable-task-sdks"

Activity functions receive a context object and an input. The context provides metadata like the orchestration ID and task ID, but most tests don't need it.

C#

Using the SayHelloActivity class from the orchestrator example, call RunAsync directly with a mock context:

[Fact]
public async Task SayHello_ReturnsExpectedGreeting()
{
    var activity = new SayHelloActivity();
    var contextMock = new Mock<TaskActivityContext>();

    var result = await activity.RunAsync(contextMock.Object, "Tokyo");

    Assert.Equal("Hello Tokyo!", result);
}

When you use DurableTaskTestHost, activities also run as part of the orchestration test. You don't need separate activity tests unless the activity has complex logic.

Python

Test the activity function directly — no special setup is required:

from durabletask import task


def hello(ctx: task.ActivityContext, name: str) -> str:
    return f"Hello {name}!"


def test_hello():
    result = hello(None, "Tokyo")
    assert result == "Hello Tokyo!"

JavaScript

Test the activity function directly:

const sayHello = async (_, name) => `Hello ${name}!`;

test("sayHello returns expected greeting", async () => {
    const result = await sayHello(undefined, "Tokyo");
    expect(result).toBe("Hello Tokyo!");
});

::: zone-end

::: zone pivot="durable-functions"

Test client functions

Client functions (also called trigger functions) start orchestrations and manage instances. They use the durable client binding to interact with the orchestration engine.

C#

Consider this HTTP trigger that starts an orchestration:

[Function("HelloCitiesOrchestration_HttpStart")]
public static async Task<HttpResponseData> HttpStart(
    [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post")] HttpRequestData req,
    [DurableClient] DurableTaskClient client,
    FunctionContext executionContext)
{
    string instanceId = await client.ScheduleNewOrchestrationInstanceAsync(
        nameof(HelloCitiesOrchestration));
    return await client.CreateCheckStatusResponseAsync(req, instanceId);
}

Mock DurableTaskClient to return a known instance ID:

[Fact]
public async Task HttpStart_ReturnsAccepted()
{
    var durableClientMock = new Mock<DurableTaskClient>("testClient");
    var functionContextMock = new Mock<FunctionContext>();
    var instanceId = "test-instance-id";

    durableClientMock
        .Setup(x => x.ScheduleNewOrchestrationInstanceAsync(
            It.IsAny<TaskName>(),
            It.IsAny<object>(),
            It.IsAny<StartOrchestrationOptions>(),
            It.IsAny<CancellationToken>()))
        .ReturnsAsync(instanceId);

    var mockRequest = CreateMockHttpRequest(functionContextMock.Object);

    var responseMock = new Mock<HttpResponseData>(functionContextMock.Object);
    responseMock.SetupGet(r => r.StatusCode).Returns(HttpStatusCode.Accepted);

    durableClientMock
        .Setup(x => x.CreateCheckStatusResponseAsync(
            It.IsAny<HttpRequestData>(),
            It.IsAny<string>(),
            It.IsAny<CancellationToken>()))
        .ReturnsAsync(responseMock.Object);

    var result = await HelloCitiesOrchestration.HttpStart(
        mockRequest, durableClientMock.Object, functionContextMock.Object);

    Assert.Equal(HttpStatusCode.Accepted, result.StatusCode);
}

Python

Consider this HTTP trigger that starts an orchestration:

@app.route(route="start")
@app.durable_client_input(client_name="client")
async def http_start(req: func.HttpRequest, client):
    instance_id = await client.start_new("my_orchestrator")
    return client.create_check_status_response(req, instance_id)

Mock the durable client:

import asyncio
import unittest
import azure.functions as func
from unittest.mock import AsyncMock, Mock

from function_app import http_start


class TestClientFunction(unittest.TestCase):
    def test_http_start(self):
        func_call = http_start.build().get_user_function().client_function

        req = func.HttpRequest(
            method="GET",
            body=b"{}",
            url="/api/start",
        )

        client = Mock()
        client.start_new = AsyncMock(return_value="test-instance-id")
        client.create_check_status_response = Mock(return_value="check_status_response")

        result = asyncio.run(func_call(req, client))

        client.start_new.assert_called_once_with("my_orchestrator")
        client.create_check_status_response.assert_called_once_with(req, "test-instance-id")

JavaScript

JavaScript unit testing for Durable Functions isn't covered in this article.

::: zone-end

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