Toxon.StepFunctionTesting 0.3.0

Toxon.StepFunctionTesting

Test AWS Step Functions state logic from .NET by running states through TestState with mocks.

Install

dotnet add package Toxon.StepFunctionTesting

What this library does

• Runs Step Function state transitions from a JSON definition
• Supports mock sequences for task outcomes (ThenReturn, ThenFail)
• Handles retries/catches via AWS Step Functions behavior
• Returns typed results (Success, Failed, CaughtError, Retriable)

Prerequisites

• .NET 8+ test project
• AWS credentials available at runtime (for states:TestState)
• IAM permission for states:TestState

This library calls the AWS Step Functions TestState API, so tests are not fully offline.

Quick start

using Amazon.StepFunctions;
using Toxon.StepFunctionTesting.Framework;

var definition = """
{
 "StartAt": "Work",
 "States": {
 "Work": {
 "Type": "Task",
 "Resource": "arn:aws:states:::lambda:invoke",
 "End": true
 }
 }
}
""";

var runner = new StepFunctionRunner(
 new AmazonStepFunctionsClient(),
 definition,
 new StepFunctionRunnerOptions { RequireMocks = true });

var mocks = new Dictionary<string, IMockProvider>
{
 ["Work"] = new MockSequence()
 .ThenReturn("{\"ok\":true}")
};

var result = await runner.RunAsync("{}", mocks);

if (result is StepFunctionStateResult.Success success)
{
 Console.WriteLine(success.Output);
}

Common mocking patterns

var mocks = new Dictionary<string, IMockProvider>
{
 ["Fetch"] = new MockSequence()
 .ThenFail("RetryableError")
 .ThenReturn("{\"value\":123}"),

 ["Validate"] = new MockSequence()
 .ThenFail("ValidationError", "missing required field")
};

Notes and limitations

• If RequireMocks is true, ALL task states must have mocks.
• SkipWaitStates is recommended for test speed, but will not evaluate any expression for wait duration or any assignments/state transformation on Wait states
• Parallel states are handled by running branches and combining outputs.
• Map states are supported for INLINE maps but not for DISTRIBUTED, however both can be mocked.

CI usage (GitHub Actions)

If you run tests in CI, ensure AWS credentials are available (for example via GitHub OIDC) and the assumed role includes states:TestState.