Testing TypeScript Types: Ensuring Type Safety in Your Code

The article discusses the importance of testing TypeScript types to ensure type safety in code. It begins by explaining the context of migrating from a REST API to a GraphQL API and the challenges that arise when dealing with different types. The author introduces the concept of type assertions and how they can be used to inform the compiler that two types are equivalent. However, the author raises concerns about the future maintainability of type assertions, as changes to the types could break the code. To address this issue, the author presents an early solution that involves converting the types into unions of string literals and visually asserting their equivalence. The article then introduces a helper type and an assert function to turn the type assertion into a type-safe assertion. By using this approach, developers can ensure that it is always safe to cast one type to another. The article concludes by emphasizing the importance of testing TypeScript types to maintain code integrity and prevent potential bugs.