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Testing infrastructure code ensures that your configurations are correct before they are deployed. tfts provides a Testing utility class to help you synthesize stacks and assert on the generated Terraform JSON.

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The Testing Class

The Testing class is the primary entry point for writing tests in tfts. It provides methods for creating test applications, synthesizing stacks, and performing assertions.

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Testing.app()

Creates a new App instance configured for testing. 
import { Testing } from "tfts";

const app = Testing.app();

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Testing.synth()

Synthesizes a stack into a JSON object that can be used for assertions. 
import { Testing, Stack } from "tfts";

const app = Testing.app();
const stack = new Stack(app, "my-stack");
// ... add resources to stack

const json = Testing.synth(stack);

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Testing.synthScope()

A helper method that creates a temporary scope, executes a callback to define resources, and returns the synthesized JSON. 
const json = Testing.synthScope((scope) => {
  new MyConstruct(scope, "my-construct");
});

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Testing.synthToJson()

Synthesizes a stack and returns the result as a formatted JSON string. 
const jsonString = Testing.synthToJson(stack);

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Testing.renderConstructTree()

Returns a visual representation of the construct tree, which is useful for debugging complex hierarchies. 
console.log(Testing.renderConstructTree(stack));

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Assertions

tfts provides several assertion methods to verify the contents of the synthesized Terraform JSON.

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Testing.toHaveResource()

Asserts that the JSON contains a resource of a specific type. You can optionally provide properties to match. 
Testing.toHaveResource(json, "aws_instance", {
  instance_type: "t3.micro"
});

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Testing.toHaveResourceWithProperties()

Similar to toHaveResource, but specifically emphasizes checking for a set of properties. 
Testing.toHaveResourceWithProperties(json, "aws_s3_bucket", {
  bucket: "my-test-bucket",
  force_destroy: true
});

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Testing.toHaveDataSource()

Asserts that the JSON contains a data source of a specific type. 
Testing.toHaveDataSource(json, "aws_ami", {
  most_recent: true
});

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Testing.toHaveProvider()

Asserts that the JSON contains a provider configuration. 
Testing.toHaveProvider(json, "aws", {
  region: "us-east-1"
});

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Example Test File

Here is a complete example of a test file using bun:test. 
import { describe, expect, it } from "bun:test";
import { Testing, Stack } from "tfts";
import { Instance } from "./.gen/providers/aws/instance";

describe("MyStack", () => {
  it("should contain an EC2 instance with correct type", () => {
    const app = Testing.app();
    const stack = new Stack(app, "test-stack");

    new Instance(stack, "web-server", {
      ami: "ami-0c55b159cbfafe1f0",
      instanceType: "t2.micro",
    });

    const json = Testing.synth(stack);

    expect(() => {
      Testing.toHaveResource(json, "aws_instance", {
        instance_type: "t2.micro",
      });
    }).not.toThrow();
  });
});