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azure-functions-test

Runs Azure Functions locally using Azure Functions Core Tools v4 (`func start`), Azurite storage emulation, and framework-native unit tests for handler code (.NET isolated worker model, Node.js v4, Python v2). Covers HTTP, queue, and timer trigger testing, admin-endpoint invocation for non-HTTP triggers, and binding verification via local.settings.json. Use when testing Azure Functions before deployment, reproducing trigger behaviour without live Azure services, or gating function handler logic in CI.

azure-functions-test

Overview

Azure Functions Core Tools v4 (func.exe) provides a local runtime that mirrors the Functions host on Azure. Per learn.microsoft.com/azure/azure-functions/functions-run-local, func start starts all triggers in the project directory and outputs the URL of every HTTP-triggered function. Azurite emulates Blob, Queue, and Table Storage locally so queue and timer triggers can be exercised without a live storage account.

Nearest neighbours and how this skill differs:

  • aws-sam-local-testing wraps SAM Local for Lambda/API Gateway. This skill is Azure-only and covers func start, Azurite, the .NET isolated worker model, and admin-endpoint invocation.
  • lambda-test-tools-net covers the .NET Lambda test runner. This skill covers the .NET isolated worker model (Microsoft.Azure.Functions.Worker).
  • serverless-integration-test-builder builds multi-function integration harnesses. This skill covers the per-function local invocation workflow.

When to use

  • Local unit + integration tests for Azure Function handlers before deploy.
  • Reproducing HTTP, queue, or timer trigger behaviour without deploying.
  • CI gating on function handler logic in .NET, Node.js, or Python.
  • Verifying binding configuration with Azurite instead of live Azure Storage.

Install

# macOS
brew tap azure/functions
brew install azure-functions-core-tools@4

# Ubuntu/Debian (see full APT steps at learn.microsoft.com/azure/azure-functions/functions-run-local#install-the-azure-functions-core-tools)
sudo apt-get install azure-functions-core-tools-4

# Windows: download the MSI from
# https://go.microsoft.com/fwlink/?linkid=2174087 (64-bit) per the Core Tools docs

Verify:

func --version   # must be 4.x

Install Azurite via npm, per learn.microsoft.com/azure/storage/common/storage-install-azurite:

npm install -g azurite

Project initialisation

# .NET isolated worker model (recommended; in-process support ends 2026-11-10
# per learn.microsoft.com/azure/azure-functions/dotnet-isolated-in-process-differences)
func init MyApp --worker-runtime dotnet-isolated

# Node.js (v4 programming model)
func init MyApp --worker-runtime javascript --model V4

# Python (v2 programming model)
func init MyApp --worker-runtime python --model V2

# Add a trigger template
func new --template "Http Trigger" --name HttpExample
func new --template "Azure Queue Storage Trigger" --name QueueExample
func new --template "Timer trigger" --name TimerExample

local.settings.json

Per learn.microsoft.com/azure/azure-functions/functions-develop-local, local.settings.json holds app settings used only when running locally. Set AzureWebJobsStorage to UseDevelopmentStorage=true to route storage triggers to Azurite:

{
  "IsEncrypted": false,
  "Values": {
    "FUNCTIONS_WORKER_RUNTIME": "dotnet-isolated",
    "AzureWebJobsStorage": "UseDevelopmentStorage=true"
  }
}

Never commit local.settings.json to source control; it may contain connection strings.

Start Azurite

Azurite emulates Blob (port 10000), Queue (port 10001), and Table (port 10002) per learn.microsoft.com/azure/storage/common/storage-install-azurite. Start it before func start:

azurite --silent --location ./azurite-data

For Docker:

docker run -p 10000:10000 -p 10001:10001 -p 10002:10002 \
    mcr.microsoft.com/azure-storage/azurite

Start the local Functions host

From the project root, per learn.microsoft.com/azure/azure-functions/functions-run-local#start-the-functions-runtime:

func start

Output includes HTTP trigger URLs, e.g.:

Http Function HttpExample: http://localhost:7071/api/HttpExample

By default, HTTP authorization is not enforced locally (all requests are treated as authLevel = "anonymous"). Pass --enableAuth to require authorization during local testing.

Testing triggers

HTTP trigger

# GET
curl http://localhost:7071/api/HttpExample?name=World

# POST
curl --request POST http://localhost:7071/api/HttpExample \
     --data '{"name":"World"}'

Non-HTTP triggers (admin endpoint)

Per learn.microsoft.com/azure/azure-functions/functions-manually-run-non-http, non-HTTP triggers can be fired via the admin endpoint. Authorization is bypassed locally:

# Queue trigger named QueueExample
curl --request POST \
     -H "Content-Type: application/json" \
     --data '{"input":"sample queue payload"}' \
     http://localhost:7071/admin/functions/QueueExample

# Timer trigger named TimerExample (empty input is valid)
curl --request POST \
     -H "Content-Type: application/json" \
     --data '{}' \
     http://localhost:7071/admin/functions/TimerExample

The endpoint returns HTTP 202 (Accepted) on success.

Unit-testing handlers

Testing handler code directly avoids the overhead of a running host. The approach differs by language.

.NET isolated worker model

The .NET isolated worker model runs function code in a separate worker process from the Functions host, per learn.microsoft.com/azure/azure-functions/dotnet-isolated-in-process-differences. The core packages are Microsoft.Azure.Functions.Worker and Microsoft.Azure.Functions.Worker.Sdk. HTTP triggers use HttpRequestData / HttpResponseData (not HttpRequest/IActionResult) unless ASP.NET Core integration is enabled.

Because handler classes can use dependency injection, extract service dependencies behind interfaces and substitute test doubles. The FunctionContext can be mocked with any standard mock library.

// Handler under test
public class HttpExample
{
    [Function("HttpExample")]
    public HttpResponseData Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req,
        FunctionContext context)
    {
        var response = req.CreateResponse(HttpStatusCode.OK);
        response.WriteString("Hello from Azure Functions");
        return response;
    }
}

// xUnit test - construct HttpRequestData via a mock FunctionContext
// (use Moq, NSubstitute, or similar for FunctionContext and HttpRequestData)
[Fact]
public async Task Run_ReturnsOk()
{
    var context = new Mock<FunctionContext>();
    var request = CreateMockHttpRequest(context.Object, HttpMethod.Get);

    var function = new HttpExample();
    var response = function.Run(request, context.Object);

    Assert.Equal(HttpStatusCode.OK, response.StatusCode);
}

Node.js (v4 programming model)

// handler.js
const { app } = require('@azure/functions');

app.http('HttpExample', {
  methods: ['GET', 'POST'],
  authLevel: 'anonymous',
  handler: async (request, context) => {
    const name = request.query.get('name') || 'World';
    return { body: `Hello, ${name}!` };
  },
});

// handler.test.js (Jest)
const { handler } = require('./handler');

test('returns greeting', async () => {
  const req = { query: new URLSearchParams('name=Test'), text: async () => '' };
  const ctx = { log: jest.fn() };
  const res = await handler(req, ctx);
  expect(res.body).toBe('Hello, Test!');
});

Python (v2 programming model)

# function_app.py
import azure.functions as func
app = func.FunctionApp()

@app.route(route="HttpExample")
def http_example(req: func.HttpRequest) -> func.HttpResponse:
    name = req.params.get('name', 'World')
    return func.HttpResponse(f"Hello, {name}!")

# test_function_app.py (pytest)
import azure.functions as func
from function_app import http_example

def test_http_example():
    req = func.HttpRequest(
        method='GET',
        url='/api/HttpExample',
        params={'name': 'Test'},
        body=b''
    )
    resp = http_example(req)
    assert resp.status_code == 200
    assert 'Test' in resp.get_body().decode()

CI integration

jobs:
  azure-functions-test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Install Core Tools
        run: |
          curl https://packages.microsoft.com/keys/microsoft.asc | gpg --dearmor > microsoft.gpg
          sudo mv microsoft.gpg /etc/apt/trusted.gpg.d/microsoft.gpg
          sudo sh -c 'echo "deb [arch=amd64] https://packages.microsoft.com/repos/microsoft-ubuntu-$(lsb_release -cs)-prod $(lsb_release -cs) main" > /etc/apt/sources.list.d/dotnetdev.list'
          sudo apt-get update && sudo apt-get install -y azure-functions-core-tools-4
      - name: Start Azurite
        run: npx azurite --silent &
      - name: Run unit tests
        run: dotnet test   # or: pytest / npm test

Anti-patterns

Anti-patternWhy it failsFix
Skip Azurite for queue/timer triggersQueue and storage triggers require AzureWebJobsStorage; without it func start errorsStart Azurite and set "AzureWebJobsStorage": "UseDevelopmentStorage=true" in local.settings.json
Use in-process model for new projectsSupport for in-process model ends 2026-11-10 per learn.microsoft.com/azure/azure-functions/dotnet-isolated-in-process-differencesUse --worker-runtime dotnet-isolated
Hard-code connection strings in codeSecrets leak to source controlUse local.settings.json Values array; it is git-ignored by default
Call admin endpoint without Content-Type: application/jsonHost rejects the requestAlways include Content-Type: application/json header and {"input":"..."} body
Commit local.settings.jsonContains secretsVerify .gitignore excludes it; use func settings to sync with Azure app settings
Use func host start for Core Tools v4Command removed in v4; it was v1.x syntax per Core Tools docsUse func start

Limitations

References