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# Integration Tests | ||
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This document describes the purpose of integration tests as well as acting as a guide | ||
on what type of changes require integrations tests and how you should write integration tests. | ||
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- [What are CDK Integration Tests](#what-are-cdk-integration-tests) | ||
- [When are integration tests required](#when-are-integration-tests-required) | ||
- [How to write Integration Tests](#how-to-write-integration-tests) | ||
- [Creating a test](#creating-a-test) | ||
- [New L2 Constructs](#new-l2-constructs) | ||
- [Existing L2 Constructs](#existing-l2-constructs) | ||
- [Assertions](#assertions) | ||
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## What are CDK Integration Tests | ||
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All Construct libraries in the CDK code base have integration tests that serve to - | ||
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1. Acts as a regression detector. It does this by running `cdk synth` on the integration test and comparing it against | ||
the `*.expected.json` file. This highlights how a change affects the synthesized stacks. | ||
2. Allows for a way to verify if the stacks are still valid CloudFormation templates, as part of an intrusive change. | ||
This is done by running `yarn integ` which will run `cdk deploy` across all of the integration tests in that package. | ||
If you are developing a new integration test or for some other reason want to work on a single integration test | ||
over and over again without running through all the integration tests you can do so using | ||
`yarn integ integ.test-name.js` .Remember to set up AWS credentials before doing this. | ||
3. (Optionally) Acts as a way to validate that constructs set up the CloudFormation resources as expected. | ||
A successful CloudFormation deployment does not mean that the resources are set up correctly. | ||
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## When are Integration Tests Required | ||
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The following list contains common scenarios where we _know_ that integration tests are required. | ||
This is not an exhaustive list and we will, by default, require integration tests for all | ||
new features unless there is a good reason why one is not needed. | ||
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**1. Adding a new feature that is using previously unused CloudFormation resource types** | ||
For example, adding a new L2 construct for an L1 resource. There should be a new integration test | ||
to test that the new L2 successfully creates the resources in AWS. | ||
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**2. Adding a new feature that is using previously unused (or untested) CloudFormation properties** | ||
For example, there is an existing L2 construct for a CloudFormation resource and you are adding | ||
support for a new property. This could be either a new property that has been added to CloudFormation | ||
or an existing property that the CDK did not have coverage for. You should either update and existing | ||
integration test to cover this new property or create a new test. | ||
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Sometimes the CloudFormation documentation is incorrect or unclear on the correct way to configure | ||
a property. This can lead to introducing new features that don't actually work. Creating | ||
an integration test for the new feature can ensure that it works and avoid unnecessary bugs. | ||
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**3. Involves configuring resource types across services (i.e. integrations)** | ||
For example, you are adding functionality that allows for service x to integrate with service y. | ||
A good example of this is the [aws-stepfunctions-tasks](./packages/@aws-cdk/aws-stepfunctions-tasks) or | ||
[aws-apigatewayv2-integrations](./packages/@aws-cdk/aws-apigatewayv2-integrations) modules. Both of these | ||
have L2 constructs that provide functionality to integrate services. | ||
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Sometimes these integrations involve configuring/formatting json/vtl or some other type of data. | ||
For these types of features it is important to create an integration test that not only validates | ||
that the infrastructure deploys successfully, but that the intended functionality works. This could | ||
mean deploying the integration test and then manually making an HTTP request or invoking a Lambda function. | ||
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**4. Adding a new supported version (e.g. a new [AuroraMysqlEngineVersion](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_rds.AuroraMysqlEngineVersion.html))** | ||
Sometimes new versions introduce new CloudFormation properties or new required configuration. | ||
For example Aurora MySQL version 8 introduced a new parameter and was not compatible with the | ||
existing parameter (see [#19145](https://github.com/aws/aws-cdk/pull/19145)). | ||
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**5. Adding any functionality via a [Custom Resource](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.custom_resources-readme.html)** | ||
Custom resources involve non-standard functionality and are at a higher risk of introducing bugs. | ||
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## How to write Integration Tests | ||
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This section will detail how to write integration tests, how they are executed and how to ensure | ||
you have good test coverage. | ||
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### Creating a Test | ||
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An integration tests is any file located in the `test/` directory that has a name that starts with `integ.` | ||
(e.g. `integ.*.ts`). | ||
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To create a new integration test, first create a new file, for example `integ.my-new-construct.ts`. | ||
The contents of this file should be a CDK app. For example, a very simple integration test for a | ||
Lambda Function would look like this: | ||
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_integ.lambda.ts_ | ||
```ts | ||
import * as iam from '@aws-cdk/aws-iam'; | ||
import * as cdk from '@aws-cdk/core'; | ||
import * as lambda from '../lib'; | ||
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const app = new cdk.App(); | ||
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const stack = new cdk.Stack(app, 'aws-cdk-lambda-1'); | ||
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const fn = new lambda.Function(stack, 'MyLambda', { | ||
code: new lambda.InlineCode('foo'), | ||
handler: 'index.handler', | ||
runtime: lambda.Runtime.NODEJS_10_X, | ||
}); | ||
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app.synth(); | ||
``` | ||
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To run the test you would run: | ||
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*Note - filename must be `*.js`* | ||
``` | ||
npm run cdk-integ integ.lambda.js | ||
``` | ||
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This will: | ||
1. Synthesize the CDK app | ||
2. `cdk deploy` to your AWS account | ||
3. `cdk destroy` to delete the stack | ||
4. Save a snapshot of the synthed CloudFormation template to `integ.lambda.expected.json` | ||
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Now when you run `npm test` it will synth the integ app and compare the result with the snapshot. | ||
If the snapshot has changed the same process must be followed to update the snapshot. | ||
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### New L2 Constructs | ||
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When creating a new L2 construct (or new construct library) it is important to ensure you have a good | ||
coverage base from which future contributions can build on. | ||
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Some general rules to follow are: | ||
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- **1 test with all default values** | ||
One test for each L2 that only populates the required properties. For a Lambda Function this would look like: | ||
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```ts | ||
new lambda.Function(this, 'Handler', { | ||
code, | ||
handler, | ||
runtime, | ||
}); | ||
``` | ||
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- **1 test with all values provided** | ||
One test for each L2 that populates non-default properties. Some of this will come down to judgement, but this should | ||
be based on major functionality. For example, when testing a Lambda Function there are 37 (*at the time of this writing) different | ||
input parameters. Some of these can be tested together and don't represent large pieces of functionality, | ||
while others do. | ||
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For example, the test for a Lambda Function might look like this. For most of these properties we are probably fine | ||
testing them together and just testing one of their values. For example we don't gain much by testing a bunch of | ||
different `memorySize` settings, as long as we test that we can `set` the memorySize then we should be good. | ||
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```ts | ||
new lambda.Function(this, 'Handler', { | ||
code, | ||
handler, | ||
runtime, | ||
architecture, | ||
description, | ||
environment, | ||
environmentEncryption, | ||
functionName, | ||
initialPolicy, | ||
insightsVersion, | ||
layers, | ||
maxEventAge, | ||
memorySize, | ||
reservedConcurrentExecutions, | ||
retryAttempts, | ||
role, | ||
timeout, | ||
tracing, | ||
}); | ||
``` | ||
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Other parameters might represent larger pieces of functionality and might create other resources for us or configure | ||
integrations with other services. For these it might make sense to split them out into separate tests so it is easier | ||
to reason about them. | ||
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A couple of examples would be | ||
(you could also mix in different configurations of the above parameters with each of these): | ||
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_testing filesystems_ | ||
```ts | ||
new lambda.Function(this, 'Handler', { | ||
filesystem, | ||
}); | ||
``` | ||
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_testing event sources_ | ||
```ts | ||
new lambda.Function(this, 'Handler', { | ||
events, | ||
}); | ||
``` | ||
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_testing VPCs_ | ||
```ts | ||
new lambda.Function(this, 'Handler', { | ||
securityGroups, | ||
vpc, | ||
vpcSubnets, | ||
}); | ||
``` | ||
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### Existing L2 Constructs | ||
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Updating an existing L2 Construct could consist of: | ||
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1. **Adding coverage for a new (or previously uncovered) CloudFormation property.** | ||
In this case you would want to either add this new property to an existing integration test or create a new | ||
integration test. A new integration test is preferred for larger update (e.g. adding VPC connectivity, etc). | ||
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2. **Updating functionality for an existing property.** | ||
In this case you should first check if you are already covered by an existing integration test. If not, then you would follow the | ||
same process as adding new coverage. | ||
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3. **Changing functionality that affects asset bundling** | ||
Some constructs deal with asset bundling (i.e. `aws-lambda-nodejs`, `aws-lambda-python`, etc). There are some updates that may not | ||
touch any CloudFormation property, but instead change the way that code is bundled. While these types of changes may not require | ||
a change to an integration test, you need to make sure that the integration tests and assertions are rerun. | ||
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An example of this would be making a change to the way `aws-lambda-nodejs` bundles Lambda code. A couple of things could go wrong that would | ||
only be caught by rerunning the integration tests. | ||
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1. The bundling commands are only running when performing a real synth (not part of unit tests). Running the integration test confirms | ||
that the actual bundling was not broken. | ||
2. When deploying Lambda Functions, CloudFormation will only update the Function configuration with the new code, | ||
but it will not validate that the Lambda function can be invoked. Because of this, it is important to rerun the integration test | ||
to deploy the Lambda Function _and_ then rerun the assertions to ensure that the function can still be invoked. | ||
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### Assertions | ||
...Coming soon... |
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