Unit Tests

Testing your application can give you faster feedback cycles and guard you against unwanted changes. Currently, testing is only supported in Typescript with jest.

We generate all files necessary to run jest when you run cdktf init so that you can start writing tests right away. If you want to add jest to an existing project, please follow their guide. Then, you need to add these lines in a setup file:

const cdktf = require("cdktf");
cdktf.Testing.setupJest();

Write Assertions

The example below uses 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.

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

import { Testing } from "cdktf";
import { Image, Container } from "../.gen/providers/docker";
import MyApplicationsAbstraction from "../app"; // Could be a class extending from cdktf.Resource

describe("Unit testing using assertions", () => {
  it("should contain a container", () => {
    expect(
      Testing.synthScope((scope) => {
        new MyApplicationsAbstraction(scope, "my-app", {});
      })
    ).toHaveResource(Container);
  });

  it("should use an ubuntu image", () => {
    expect(
      Testing.synthScope((scope) => {
        new MyApplicationsAbstraction(scope, "my-app", {});
      })
    ).toHaveResourceWithProperties(Image, { name: "ubuntu:latest" });
  });
});

Snapshot Testing

Snapshot tests are useful when you want to make sure your infrastructure does not change unexpectedly. You can read more about them in the Jest docs.

import { Testing } from "cdktf";
import { Image, Container } from "../.gen/providers/docker";
import MyApplicationsAbstraction from "../app"; // Could be a class extending from cdktf.Resource

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
  });
});

Integration with Terraform

You can produce invalid Terraform configuration if you are using escape hatches in your CDK for Terraform 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 cdktf plan or cdktf deploy.

import { Testing } from "cdktf";

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();
  });
});

Integration Testing

CDK for Terraform 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.