In Kotlin development, effective dependency management is crucial for maintaining clean and scalable code, often achieved through Dependency Injection (DI), a design pattern that promotes modularity by decoupling class behavior from dependency creation. Dagger is a powerful DI framework used in Kotlin applications to simplify object lifecycle and dependency management. This guide illustrates how DI can be applied in a subscription-based SaaS product, emphasizing contract testing to ensure components meet expected interactions through injected dependencies. It provides a step-by-step tutorial on setting up a project with Dagger, implementing a subscription system with billing and subscription services, and automating contract testing using CircleCI. The guide also includes instructions for configuring the project's environment, defining data models, designing business logic for subscription management, and setting up a CI pipeline on CircleCI to automate testing, ensuring consistency and reliability. This approach enhances code modularity and testability, offering a foundation for integrating additional services or features in the future.