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Testing programmatically

The Simulator target (sim)

In addition to cloud services as backends, the Wing SDK is shipped with built-in support for a simulator backend for each resource. The simulator provides a fully-functional implementation for the cloud resources you use in your application.

For example, the simulated implementation of cloud.Queue is simply an in-memory array of items.

Compiling your program

So now, we return to the root of the project and compile our app and target the cloud simulator using the following command:

cd ../../../../
wing compile -t sim hello.w

Compilation output

This would create a new file at target/hello.wsim which is the simulated version of your entire cloud application.

Now that we have an hello.wsim file, we can either interact with through the Wing Console or load it into a Simulator class which is shipped as part of the Wing SDK and use it programmatically.

This means that, for example, you can interact with your simulated Wing application directly from the Node.js CLI.


If you are using the Wing CLI through a global installation, you'll need to install the Wing SDK library locally using:

npm i @winglang/sdk

Starting Node.js

Start Node.js (with experimental await support):

node --experimental-repl-await

Start the simulator

Now, we import the Wing SDK library:

const sdk = require("@winglang/sdk"); // import the wing sdk library
const simulator = new sdk.testing.Simulator({ simfile : "./target/hello.wsim"}); // create an instance of the Simulator
await simulator.start(); // start the simulator

Now that our app is running, lets trigger a message on the queue

Trigger a message to the queue

For example, we can list all the resources in the app:

 const queue = simulator.getResource("root/cloud.Queue"); // retrieve the queue resource
await queue.push("Wing")

Viewing generated file

const bucket = simulator.getResource("root/cloud.Bucket"); // retrieve the bucket resource
await bucket.list() // will show available files
await bucket.get("wing.txt") // will show the file content

The result of the last two function calls will be

[ 'wing.txt' ]
'Hello, Wing'

Congratulations! 🚀

You've just tested your cloud application through the Simulator class