Topic 12. Working with files, data serialization with kotlinx.serialization, and unit testing

Goal: learn to define a file format, validate external data, serialize models, and prove the behavior of storage with isolated unit tests.

Lecture contents

1. Files, text, and bytes — The path and the working directory · Text, bytes, and closing resources · Example 1. An event log
2. Safe writing and CSV format — I/O errors and safe replacement · CSV: a format has a contract
3. JSON serialization — Adding kotlinx.serialization and tests · JSON and serializable models · Dates and a custom serializer
4. Unit testing — A unit test as an executable contract · Running, reports, and coverage

Practice and review

• Practice — 3 worked examples with complete code and execution results
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links