Fluent AssertJ-like Library For Testing AWS CDK Stack
2 min readJun 5, 2023
AWS CDK testing framework
AWS offers a framework to verify that your stack is well-formed and that it matches your expectations. This framework can be found here.
Here is an example of the stack containing a specific role:
template.hasResourceProperties("AWS::IAM::Role", Match.objectEquals(
Collections.singletonMap("AssumeRolePolicyDocument", Map.of(
"Version", "2012-10-17",
"Statement", Collections.singletonList(Map.of(
"Action", "sts:AssumeRole",
"Effect", "Allow",
"Principal", Collections.singletonMap(
"Service", Collections.singletonMap(
"Fn::Join", Arrays.asList(
"",
Arrays.asList("states.", Match.anyValue(), ".amazonaws.com")
)
)
)
))
))
));AWS CDK testing fluent library
While working on a small open-source project, I was maintaining a CDK stack containing some resources. I noticed that the tests written using the AWS framework were verbose and presented challenges in terms of readability and maintainability. In response, I decided to create a small library to make it easier to read, write and maintain tests.
To illustrate, an equivalent representation to the aforementioned example can be found below: as follows”
CDKStackAssert.assertThat(template)
.containsRoleWithManagedPolicyArn(managedPolicyArn)
.hasAssumeRolePolicyDocument("states.amazonaws.com", null, "Allow", "2012-10-17", "sts:AssumeRole");How to use it
- The library is available on Maven Central. To use it, add the following dependency to your project:
<dependency>
<groupId>cloud.pianola</groupId>
<artifactId>cdk-fluent-assertions</artifactId>
<version>1.0.1</version>
<scope>test</scope>
</dependency>- Create a class
TemplateSupportin your testing packages. This class will be used to load the template and create theCDKStackAssertobject.
public abstract class TemplateSupport {
public static final String ENV = "test";
public static final String TEST_CDK_BUCKET = "test-cdk-bucket";
public static final String QUALIFIER = "test";
static Template template;
private static final String STACK_NAME = "example-lambda-function-test-stack";
@TempDir
private static Path TEMP_DIR;
@BeforeAll
static void initAll() throws IOException {
final Path lambdaCodePath = TestLambdaUtils.getTestLambdaCodePath(TEMP_DIR);
final Map<String, String> tags = createTags(ENV, TAG_VALUE_COST_CENTRE);
final App app = new App();
final ExampleLambdaStack stack = StackUtils.createStack(app, STACK_NAME, lambdaCodePath.toString(), QUALIFIER, TEST_CDK_BUCKET, ENV);
tags.entrySet().stream()
.filter(tag -> Objects.nonNull(tag.getValue()))
.forEach(tag -> Tags.of(app).add(tag.getKey(), tag.getValue()));
template = Template.fromStack(stack);
}
@AfterAll
static void cleanup() {
template = null;
}
}- Extend the
TemplateSupportclass in your test classes and use theCDKStackAssertobject to verify your stack.
class LambdaTest extends TemplateSupport {
public static final String TEST = "test";
@Test
void should_have_lambda_function() {
CDKStackAssert.assertThat(template)
.containsFunction("example-lambda-function")
.hasHandler("org.springframework.cloud.function.adapter.aws.FunctionInvoker::handleRequest")
.hasCode("test-cdk-bucket", "(.*).zip")
.hasRole("examplelambdafunctionrole(.*)")
.hasDependency("examplelambdafunctionrole(.*)")
.hasDependency("examplelambdafunctionroleDefaultPolicy(.*)")
.hasTag("COST_CENTRE", TAG_VALUE_COST_CENTRE)
.hasTag("ENV", TEST)
.hasEnvironmentVariable("ENV", TEST)
.hasEnvironmentVariable("SPRING_PROFILES_ACTIVE", TEST)
.hasDescription("Lambda example")
.hasMemorySize(512)
.hasRuntime("provided.al2")
.hasTimeout(3);
}
}