azure/policy-emulator-testing

Policy Emulator Testing Patterns

This skill describes how to write tests for gateway emulator policy handlers in the Azure API Management policy toolkit.

Test File — test/Test.Testing/Emulator/Policies/{PolicyName}Tests.cs

File Template

// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.

namespace Test.Emulator.Emulator.Policies;

[TestClass]
public class {PolicyName}Tests
{
    // Inner document class implementing IDocument
    class Simple{PolicyName} : IDocument
    {
        public void Inbound(IInboundContext context)
        {
            context.{PolicyName}(new {PolicyName}Config
            {
                // config properties
            });
        }
        public void Outbound(IOutboundContext context) { }
        public void Backend(IBackendContext context) { }
        public void OnError(IOnErrorContext context) { }
    }

    [TestMethod]
    public void Should{ExpectedBehavior}()
    {
        // Arrange
        var test = new Simple{PolicyName}().AsTestDocument();

        // Act
        test.RunInbound();

        // Assert (using FluentAssertions)
        test.Context.{assertion};
    }
}

Key Conventions

• Namespace: Test.Emulator.Emulator.Policies (matches existing test convention)
• Class name: {PolicyName}Tests
• Framework: MSTest ([TestClass], [TestMethod])
• Assertions: FluentAssertions
• Test document creation: new SimpleDocument().AsTestDocument() extension method (or new TestDocument(new SimpleDocument()) — both are equivalent)
• Inner document classes implement IDocument with all four section methods. Unused sections have empty bodies.
• Section execution: test.RunInbound(), test.RunOutbound(), test.RunBackend(), test.RunOnError()

Required Test Coverage

Each policy must have tests covering:

1. Basic Execution

Create a document with the policy call, run through TestDocument, assert context state changes:

[TestMethod]
public void ShouldModifyContextState()
{
    var test = new SimpleSetStatus().AsTestDocument();

    test.RunInbound();

    test.Context.Response.StatusCode.Should().Be(200);
    test.Context.Response.StatusReason.Should().Be("OK");
}

2. Callback Override

Verify that SetupInbound() (or appropriate section) .{PolicyName}().WithCallback(...) correctly overrides default behavior:

[TestMethod]
public void ShouldExecuteCallback()
{
    var test = new Simple{PolicyName}().AsTestDocument();

    test.SetupInbound()
        .{PolicyName}()
        .WithCallback((context, config) =>
        {
            context.Variables["test"] = "value";
        });

    test.RunInbound();

    test.Context.Variables.Should().ContainKey("test")
        .WhoseValue.Should().Be("value");
}

3. Predicate-Based Mock

For policies called multiple times with different configs in the same section:

[TestMethod]
public void ShouldSelectCorrectCallback()
{
    var test = new Multi{PolicyName}().AsTestDocument();

    test.SetupInbound()
        .{PolicyName}((ctx, config) => config.SomeProperty == "A")
        .WithCallback((ctx, cfg) => { /* handle A */ });

    test.SetupInbound()
        .{PolicyName}((ctx, config) => config.SomeProperty == "B")
        .WithCallback((ctx, cfg) => { /* handle B */ });

    test.RunInbound();
    // Assert...
}

4. Pre-configured Context

When the handler depends on existing context state:

[TestMethod]
public void ShouldHandleExistingHeaders()
{
    var test = new Simple{PolicyName}().AsTestDocument();
    test.Context.Request.Headers["Content-Type"] = ["application/json"];

    test.RunInbound();

    test.Context.Request.Headers.Should().ContainKey("Content-Type");
}

5. Error/Exception Scenarios

Not all policies support .WithError(). This API is specific to certain mock providers (e.g., MockAuthenticationManagedIdentityProvider). For policies without a dedicated error API, simulate errors via callbacks:

[TestMethod]
public void ShouldSimulateError()
{
    var test = new Simple{PolicyName}().AsTestDocument();

    test.SetupInbound()
        .{PolicyName}()
        .WithCallback((context, config) =>
        {
            context.Response.StatusCode = 500;
            context.Response.StatusReason = "Internal Server Error";
            throw new FinishSectionProcessingException();
        });

    test.RunInbound();

    test.Context.Response.StatusCode.Should().Be(500);
}

For authentication policies that have .WithError():

[TestMethod]
public void ShouldThrowOnError()
{
    var test = new SimpleAuthenticationManagedIdentity().AsTestDocument();

    test.SetupInbound()
        .AuthenticationManagedIdentity()
        .WithError("InternalServerError");

    var ex = Assert.ThrowsException<PolicyException>(() => test.RunInbound());
    ex.Policy.Should().Be("AuthenticationManagedIdentity");
}

6. Multi-Section Tests

If the policy is available in multiple sections, add one test per section:

[TestMethod]
public void ShouldWorkInOutboundSection()
{
    var test = new Outbound{PolicyName}().AsTestDocument();

    test.RunOutbound();

    test.Context.{assertion};
}

Mock Setup Patterns

Token Provider Hook (Authentication policies)

test.SetupInbound()
    .AuthenticationManagedIdentity()
    .WithTokenProviderHook((resource, clientId) => $"{resource}{clientId}/token");

Return Value (Authentication, Cache)

test.SetupInbound()
    .AuthenticationManagedIdentity()
    .ReturnsToken("mock-token");

Cache Store Setup

test.SetupCacheStore()
    .WithExternalCacheSetup()
    .WithExternalCacheValue("key", "test");

test.SetupCacheStore().WithInternalCacheValue("key", "test");

Response Example Store (MockResponse)

var example = new ResponseExample(200, "{ \"ok\": true }", "application/json");
test.SetupResponseExampleStore().Add(test.Context, example);

Test Infrastructure

Tests rely on shared infrastructure that you do not need to modify:

• TestDocument (src/Testing/TestDocument.cs) — Wraps an IDocument and executes sections through proxies. Catches FinishSectionProcessingException gracefully.
• .AsTestDocument() extension method — Creates TestDocument from IDocument.
• SetupInbound()/SetupOutbound()/etc. — Returns MockPoliciesProvider<TSection> for fluent mock configuration.
• GatewayContext (src/Testing/GatewayContext.cs) — Contains mock request/response, variables, and emulator stores.
• Usings.cs (test/Test.Testing/Usings.cs) — Global usings for FluentAssertions and Microsoft.VisualStudio.TestTools.UnitTesting.

Build and Test Commands

# Run all emulator tests
dotnet test --project test/Test.Testing

# Run tests for a specific policy
dotnet test --project test/Test.Testing --filter "FullyQualifiedName~{PolicyName}Tests"