Testing utilities and assertions for CDK libraries

> This API may emit warnings. Backward compatibility is not guaranteed.

Replacement recommended

This library has been deprecated. We recommend you use the @aws-cdk/assertions module instead.

This library contains helpers for writing unit tests and integration tests for CDK libraries

Unit tests

Write your unit tests like this:

const stack = new Stack();

new MyConstruct(stack, 'MyConstruct', {
    ...
});

expect(stack).to(someExpectation(...));

Here are the expectations you can use:

Verify (parts of) a template

Check that the synthesized stack template looks like the given template, or is a superset of it. These functions match logical IDs and all properties of a resource.

matchTemplate(template, matchStyle)
exactlyMatchTemplate(template)
beASupersetOfTemplate(template)

Example:

expect(stack).to(beASupersetOfTemplate({
    Resources: {
        HostedZone674DD2B7: {
            Type: "AWS::Route53::HostedZone",
            Properties: {
                Name: "test.private.",
                VPCs: [{
                    VPCId: { Ref: 'VPC06C5F037' },
                    VPCRegion: { Ref: 'AWS::Region' }
                }]
            }
        }
    }
}));

Check existence of a resource

If you only care that a resource of a particular type exists (regardless of its logical identifier), and that some of its properties are set to specific values:

haveResource(type, subsetOfProperties)
haveResourceLike(type, subsetOfProperties)

Example:

expect(stack).to(haveResource('AWS::CertificateManager::Certificate', {
    DomainName: 'test.example.com',
    // Note: some properties omitted here

    ShouldNotExist: ABSENT
}));

The object you give to haveResource/haveResourceLike like can contain the following values:

• Literal values: the given property in the resource must match the given value exactly.
• ABSENT: a magic value to assert that a particular key in an object is not set (or set to undefined).
• special matchers for inexact matching. You can use these to match values based on more lenient conditions than the default (such as an array containing at least one element, ignoring the rest, or an inexact string match).

The following matchers exist:

• objectLike(O) - the value has to be an object matching at least the keys in O (but may contain more). The nested values must match exactly.
• deepObjectLike(O) - as objectLike, but nested objects are also treated as partial specifications.
• exactValue(X) - must match exactly the given value. Use this to escape from deepObjectLike's leniency back to exact value matching.
• arrayWith(E, [F, ...]) - value must be an array containing the given elements (or matchers) in any order.
• stringLike(S) - value must be a string matching S. S may contain * as wildcard to match any number of characters. Multiline strings are supported.
• anything() - matches any value.
• notMatching(M) - any value that does NOT match the given matcher (or exact value) given.
• encodedJson(M) - value must be a string which, when decoded as JSON, matches the given matcher or exact value.

Slightly more complex example with array matchers:

expect(stack).to(haveResourceLike('AWS::IAM::Policy', {
  PolicyDocument: {
    Statement: arrayWith(objectLike({
      Action: ['s3:GetObject'],
      Resource: ['arn:my:arn'],
    }})
  }
}));

Capturing values from a match

Special Capture matchers exist to capture values encountered during a match. These can be used for two typical purposes:

• Apply additional assertions to the values found during a matching operation.
• Use the value found during a matching operation in a new matching operation.

Capture matchers take an inner matcher as an argument, and will only capture the value if the inner matcher succeeds in matching the given value.

Here's an example which asserts that a policy for RoleA contains two statements with different ARNs (without caring what those ARNs might be), and that a policy for RoleB also has a statement for one of those ARNs (again, without caring what the ARN might be):

const arn1 = Capture.aString();
const arn2 = Capture.aString();

expect(stack).to(haveResourceLike('AWS::IAM::Policy', {
  Roles: ['RoleA'],
  PolicyDocument: {
    Statement: [
      objectLike({
        Resource: [arn1.capture()],
      }),
      objectLike({
        Resource: [arn2.capture()],
      }),
    ],
  },
}));

// Don't care about the values as long as they are not the same
expect(arn1.capturedValue).not.toEqual(arn2.capturedValue);

expect(stack).to(haveResourceLike('AWS::IAM::Policy', {
  Roles: ['RoleB'],
  PolicyDocument: {
    Statement: [
      objectLike({
        // This ARN must be the same as ARN1 above.
        Resource: [arn1.capturedValue]
      }),
    ],
  },
}));

NOTE: Capture look somewhat like bindings in other pattern matching libraries you might be used to, but they are far simpler and very deterministic. In particular, they don't do unification: if the same Capture is either used multiple times in the same structure expression or matches multiple times, no restarting of the match is done to make them all match the same value: the last value encountered by the Capture (as determined by the behavior of the matchers around it) is stored into it and will be the one available after the match has completed.

Check number of resources

If you want to assert that n number of resources of a particular type exist, with or without specific properties:

countResources(type, count)
countResourcesLike(type, count, props)

Example:

expect(stack).to(countResources('AWS::ApiGateway::Method', 3));
expect(stack).to(countResourcesLike('AWS::ApiGateway::Method', 1, {
  HttpMethod: 'GET',
  ResourceId: {
    "Ref": "MyResource01234"
  }
}));

Check existence of an output

haveOutput assertion can be used to check that a stack contains specific output. Parameters to check against can be:

• outputName
• outputValue
• exportName

If outputValue is provided, at least one of outputName, exportName should be provided as well

Example

expect(synthStack).to(haveOutput({
  outputName: 'TestOutputName',
  exportName: 'TestOutputExportName',
  outputValue: {
    'Fn::GetAtt': [
      'TestResource',
      'Arn'
    ]
  }
}));