Debug: Moshi JSON Library

A live debugging round on an unfamiliar codebase: you are given a deliberately broken version of the Java JSON library Moshi and must use its test suite to locate and fix the planted bugs while narrating your reasoning. The Task This is a debugging exercise on a codebase you have not seen before. You are given a version of the Java library Moshi that has bugs hidden inside on purpose. You must use the included tests and your debugging skills to find and fix these bugs. This round checks whether you can: Work with code you have not seen before. Understand unfamiliar, non-trivial code quickly. Use tooling to localize errors. Explain your steps clearly as you work. Interview Details Time: ~45-60 minutes Setup: Download the code, work on your own machine, and share your screen. Language: Java Process: The interviewer watches you work; think out loud and explain your reasoning. About Moshi Moshi is a JSON library for Android and Java by Square. It parses JSON and is meant to replace Gson with better performance and Kotlin support. Key features: Type-Safe Parsing: Safely converts JSON into Java/Kotlin objects. Streaming API: Uses very little memory when reading large JSON files. Custom Adapters: Add your own rules for specific types. Annotation Support: @Json matches fields, @JsonQualifier handles special cases. Null Safety: Strict about null values and missing data. Code Example: Moshi moshi = new Moshi.Builder().build(); JsonAdapter<User> adapter = moshi.adapter(User.class); // Convert JSON string into a Java object User user = adapter.fromJson("{\"name\":\"John\",\"age\":30}"); // Convert Java object back into a JSON string String json = adapter.toJson(user); You do not need prior Moshi knowledge. The code ships with many tests that reveal what is wrong. How to Start The bugged codebase is distributed as a downloadable archive (a Google Drive link is provided at the start of the session). Download the code and go to the debug-moshi folder. Build the project: ./gradlew build Run the tests: ./gradlew test Look at which tests fail and start investigating. Tips for Debugging Run all tests to see exactly what is broken: ./gradlew test Focus on one failure at a time to make the output easier to read: ./gradlew test --tests "ClassName.testMethodName" Read the test to see what behavior it expects. Follow the code from input to the point of failure. Use the debugger — set breakpoints in the parsing logic (e.g. Right-click the test → Debug in IntelliJ IDEA, or Debug As → JUnit Test in Eclipse). Search by keyword to find the code responsible for handling the data.