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Testing your application can give you faster feedback cycles and guard you against unwanted changes. Testing is currently supported in Typescript with jest and compatible with any testing framework that supports assertions for all other languages. We generate all files necessary to start testing when you run cdktn init so that you can start writing tests right away.

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Add Testing to Your Application

If you would like to add testing to an existing project, refer the following resources according to your chosen language:
  • TypeScript: Follow TypeScript’s Getting Started guide for testing with Jest. Then, add these lines in a setup file: 
    const cdktn = require("cdktn");
cdktn.Testing.setupJest();
  • Python: Follow the Get Started guide for pytest. The assertions for CDKTN are available in the cdktn package under Testing.
  • Java: Follow the Using JUnit documentation. The assertions for CDKTN specific are available in the cdktn package under Testing.
  • C#: Follow the Getting Started with xUnit.net guide. The assertions for CDKTN are available in the cdktn package under Testing.
  • Go: Follow the Add a Test guide in the Go documentation. The assertions for CDKTN specific are available in the cdktn package under Testing.

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Write Assertions

The following Typescript example uses Testing.synth to test a part of the application. Given the desired scope to test, a JSON string representing the synthesized HCL-JSON is returned. Then the custom assertions under Testing in the cdktn package can be used to verify the code acts as intended. Testing.synth can test the Stack that extends the TerraformStack. The other examples use Testing.synthScope to test a part of the application. This creates a scope to test a subset of the application and returns a JSON string representing the synthesized HCL-JSON. Then it uses custom matchers to verify the code acts as intended. Testing.synthScope can test the Constructs that extends the IConstruct.
CDK Terrain v0.20 introduces support for a Testing.synthHcl function. However, that is not compatible with other assertions, like toHaveResourceWithProperties etc. and should not be used.
Examples in
  • toHaveResource: Checks if a certain resource exists
  • toHaveResourceWithProperties: Checks if a certain resource exists with all properties passed
  • toHaveDataSource: Checks if a certain data source exists
  • toHaveDataSourceWithProperties: Checks if a certain data source exists with all properties passed
  • toHaveProvider: Checks if a certain provider exists
  • toHaveProviderWithProperties: Checks if a certain provider exists with all properties passed
import { Testing } from "cdktn";
import { Image } from "../.gen/providers/docker/image";
import { Container } from "../.gen/providers/docker/container";
import MyApplicationsAbstraction from "../app"; // Could be a class extending from Construct

describe("Unit testing using assertions", () => {
  it("should contain a container", () => {
    const app = Testing.app();
    const stack = new MyApplicationsAbstraction(app, "my-app", {});
    const synthesized = Testing.synth(stack);

    expect(synthesized).toHaveResource(Container);
  });

  it("should use an ubuntu image", () => {
    const app = Testing.app();
    const stack = new MyApplicationsAbstraction(app, "my-app", {});
    const synthesized = Testing.synth(stack);

    expect(synthesized).toHaveResourceWithProperties(Image, {
      name: "ubuntu:latest",
    });
  });
});

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Snapshot Testing

Snapshot tests are useful when you want to make sure your infrastructure does not change unexpectedly. Snapshot Testing is only supported in Typescript with Jest. Refer to the Jest docs for details. 
import { Testing } from "cdktn";
import { Image } from "../.gen/providers/docker/image";
import { Container } from "../.gen/providers/docker/container";
import MyApplicationsAbstraction from "../app"; // Could be a class extending from Construct

describe("Unit testing using snapshots", () => {
  it("Tests a custom abstraction", () => {
    expect(
      Testing.synthScope((stack) => {
        const app = new MyApplicationsAbstraction(scope, "my-app", {});
        app.addEndpoint("127.0.0.1"); // This could be a method your class exposes
      }),
    ).toMatchInlineSnapshot(); // There is also .toMatchSnapshot() to write the snapshot to a file
  });
});

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Integration with Terraform

You can produce invalid Terraform configuration if you are using escape hatches in your CDK Terrain application. You may use an escape hatch when setting up a remote backend or when overriding resource attributes To test this, you can assert that terraform validate or terraform plan run successfully on all or part of your application before running cdktn plan or cdktn deploy. Currently only Typescript is capable of testing for successful plans, while all languages are capable of testing for validity of the Terraform produced. 
import { Testing } from "cdktn";

describe("Checking validity", () => {
  it("check if the produced terraform configuration is valid", () => {
    const app = Testing.app();
    const stack = new TerraformStack(app, "test");

    const myAbstraction = new MyApplicationsAbstraction(stack, "my-app", {});
    myAbstraction.addEndpoint("127.0.0.1"); // This could be a method your class exposes

    // We need to do a full synth to validate the terraform configuration
    expect(Testing.fullSynth(stack)).toBeValidTerraform();
  });

  it("check if this can be planned", () => {
    const app = Testing.app();
    const stack = new TerraformStack(app, "test");

    const myAbstraction = new MyApplicationsAbstraction(stack, "my-app", {});
    myAbstraction.addEndpoint("127.0.0.1"); // This could be a method your class exposes

    // We need to do a full synth to plan the terraform configuration
    expect(Testing.fullSynth(stack)).toPlanSuccessfully();
  });
});

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Integration Testing

CDK Terrain does not currently offer many helpers for integration testing, but you can create them for your use cases. Here is a recent example: CDK Day 2021.