Testing types in TypeScript is crucial for SDK and API developers to ensure predictable type inferences. Tools like `tsc`, `dtslint`, `tsd`, and `Vitest` can help catch errors early and guarantee type behavior.
Private fields in TypeScript can be declared with either "private" or "#". The private keyword only enforces privacy at design time through the TypeScript compiler, while the "#" syntax creates Private Elements that are also protected from outside access at runtime. Private Elements provide stronger encapsulation because their fields remain completely hidden from anything outside the class.
Mutation testing evaluates the quality of your test suite by introducing small changes (mutations) to your code and checking if your tests can detect them. This tutorial will guide you through understanding mutation testing, setting up Stryker for TypeScript, and using it to enhance your test suite and code quality.