A MuleSoft developer must implement an API as a Mule application, run the application locally, and execute unit tests against the running application.

Anypoint Studio is MuleSoft's integrated development environment (IDE) specifically designed for developing, running, and testing Mule applications. It provides a graphical interface for building integration flows, includes an embedded Mule runtime for local execution and debugging, and integrates the MUnit testing framework for creating and running unit tests. This single tool fulfills all the requirements stated in the scenario: implementing the API logic, running it on a local machine, and executing unit tests against the local instance.

A. Anypoint CLI: The Anypoint Command Line Interface (CLI) is primarily used for automating CI/CD tasks, such as deploying applications and managing platform assets, not for the core development or unit testing of Mule flows.

B. API Designer: API Designer is a web-based tool used for designing and documenting API specifications (like RAML or OAS). It is used for the design phase, not for implementing the backend logic or running unit tests.

D. API Manager: API Manager is used for governing and securing deployed APIs by applying policies, managing access, and monitoring traffic. It operates on APIs that have already been implemented and deployed, not during the development phase.

1. MuleSoft Documentation, "Anypoint Studio": "Anypoint Studio is MuleSoft’s integrated development environment (IDE) for designing, building, and testing Mule applications. Studio provides tooling to create, test, and run Mule applications on-premises or in the cloud." (Reference: Anypoint Studio 7, Introduction to Anypoint Studio).

2. MuleSoft Documentation, "MUnit": "MUnit is a Mule application testing framework that allows you to easily build automated tests for your integrations and APIs. It is fully integrated with Anypoint Studio, providing a seamless experience for developers to create, run, and analyze tests." (Reference: MUnit 2.3, Introduction to MUnit).

3. MuleSoft Documentation, "API Designer": "API Designer is a web-based, graphical tool that you use to design, document, and test APIs. You can create an API specification in API Designer and then use the specification to create an API portal and to generate connectors." (Reference: Anypoint Platform, API Designer).

4. MuleSoft Documentation, "API Manager": "Use API Manager to manage your API from the cloud, controlling access and traffic by applying pre-built or custom policies. You can also use API Manager to create alerts to help you monitor your API’s performance." (Reference: Anypoint Platform, API Manager).