Support standalone execution of integrations.

[thantos]

Integrations should be executable outside of resource closures in certain cases for the following use cases:

• Testing

• Using logic during synthesis

• Create standalone integration type

• Implement standalone for

  • Express Step Function - Executes the closure
  • Lambda - As part of feat: native typescript lambda function code #103

• Fail for all other uses

  • Step Function - Illogical, step function returns the execution name, not a result
  • Event Bus - Illogical, what does it mean to submit an event locally?
  • $AWS.* and $SFN.* integrations

• Support nested standalone integrations

• Mock integrations

Valid Use:

const sfn = new ExpressionStepFunction<undefined, string>(() => {
    return "hello";
});

const result = sfn();

expect(result).toeEqual({ output: "hello", status: "SUCCEEDED" });

Invalid Use:

const sfn = new StepFunction<undefined, string>(() => {
    return "hello";
});

const result = sfn(); // invalid - what does it mean to start a long running execution locally?

Nested Use

const sfn = new ExpressionStepFunction<undefined, string>(() => {
    return "hello";
});

const sfn2 = new ExpressionStepFunction<undefined, string>(() => {
    return `${sfn()} there`;
});

const result = sfn2();

expect(result).toeEqual({ output: "hello there", status: "SUCCEEDED" });

Invalid nested

const eb = new EventBus();
const sfn = new ExpressionStepFunction<undefined, string>(() => {
    eb();
});

const result = sfn(); // fails, eb() does not support standalone;

Mocked Nested

const eb = new EventBus();
const sfn = new ExpressionStepFunction<undefined, string>(() => {
    eb();
});
mockIntegration(eb, () => {});

const result = sfn(); // success! eb is mocked

[tvanhens]

This is a longer term goal but I believe we can offer a similar experience for non-express step functions. Even though they don't return synchronously, we can expose an integration for DescribeExecution. Users could then write async tests locally by polling for the result.

We could do similar things with queues and event buses.