AWS CodeBuild is a fully managed build service that compiles source code, runs tests, and produces packages that are ready to deploy. It can be used to build, test, and deploy your code for Lambda functions as part of a continuous integration and delivery (CI/CD) pipeline.

Here's an example of how you could set up a CI/CD pipeline using AWS CodeBuild for a Lambda function:

1. Set up a source control system (e.g. Git) to track your code changes.

2. Create a build project in AWS CodeBuild. You will need to specify the source provider (e.g. GitHub), the location of the source code (e.g. a specific branch), and the build environment (e.g. runtime and version of Node.js). You can also specify build commands and test commands to be run during the build process.

3. Set up an AWS CodePipeline pipeline that triggers a new build every time there is a change to the source code. You can set up the pipeline to automatically deploy the built package to Lambda whenever the build succeeds.

4. Modify your code and commit the changes to the source control system. This will trigger a new build in AWS CodePipeline, which will pass the built package to Lambda for deployment.

By following this process, you can automate the build, test, and deployment of your Lambda functions, ensuring that your code is always up-to-date and tested.