Analyze and document the C# library

Copilot can propose an explanation, but the code and observed behavior are the authority. #codebase performs retrieval; it does not guarantee every source file was inspected or every claim is correct.

Lab briefing

[!NOTE] Source references must name real types, registrations and working directories.

Concepts · First task · Evidence checklist · Reset

Learning objectives

• Trace behavior through the console, application core and infrastructure.
• Explain physical book copies, loans and patrons accurately.
• Produce run instructions that work from a stated directory.

Before you start

Complete C# setup, then prepare 02-csharp. The bundled fixture is AccelerateDevGHCopilot. No remote clone or new GitHub repository is required.

Concepts and use cases

Exercise scenario

A teammate has delivered a small library console app without sufficient onboarding documentation. Write a README that distinguishes implemented features, limitations, and proposed work.

Task 1 - Establish the source and baseline

1. Open the prepared root. Inspect all four project files.

2. Run:

   dotnet build src/Library.Console/Library.Console.csproj -m:1 -p:UseSharedCompilation=false
   dotnet test tests/UnitTests/UnitTests.csproj -m:1 -p:UseSharedCompilation=false
   

3. Record the commands, tests, errors and warnings. Do not copy a transcript from a different run.

4. Read src/Library.Console/appSettings.json. The console uses its working directory to locate this file and the Json directory.

Task 2 - Ask for a source-grounded trace

Trace returning a loan from ConsoleApp through ILoanService and the JSON repository.
Cite the files and relevant methods. Explain how Book, BookItem, Loan, and Patron
relate. List unverified assumptions and existing error-handling limitations.
Do not edit or publish anything.

Verify each relationship manually. A book title is not a physical BookItem. A Loan relates a physical copy to a patron and carries its own dates.

---
config:
  theme: base
  look: classic
  themeVariables:
    darkMode: false
    background: "#ffffff"
    primaryColor: "#f5f5f5"
    primaryTextColor: "#111111"
    primaryBorderColor: "#555555"
    secondaryColor: "#e0e0e0"
    secondaryTextColor: "#111111"
    secondaryBorderColor: "#666666"
    tertiaryColor: "#bdbdbd"
    tertiaryTextColor: "#111111"
    tertiaryBorderColor: "#444444"
    lineColor: "#444444"
    textColor: "#111111"
    mainBkg: "#f5f5f5"
    nodeBorder: "#555555"
    clusterBkg: "#ffffff"
    clusterBorder: "#999999"
    edgeLabelBackground: "#ffffff"
    actorBkg: "#e0e0e0"
    actorBorder: "#555555"
    actorTextColor: "#111111"
    actorLineColor: "#777777"
    signalColor: "#333333"
    signalTextColor: "#111111"
    labelBoxBkgColor: "#f5f5f5"
    labelBoxBorderColor: "#777777"
    labelTextColor: "#111111"
    loopTextColor: "#111111"
    activationBkgColor: "#bdbdbd"
    activationBorderColor: "#555555"
    noteBkgColor: "#f5f5f5"
    noteTextColor: "#111111"
    noteBorderColor: "#777777"
    attributeBackgroundColorOdd: "#f5f5f5"
    attributeBackgroundColorEven: "#e0e0e0"
---
classDiagram
    accTitle: C# library dependency boundaries
    accDescr: The console depends on service contracts, application services depend on repository contracts, and JSON infrastructure implements storage behavior.
    class ConsoleApp
    class LoanService
    class ILoanRepository
    class JsonLoanRepository
    class JsonData
    ConsoleApp --> LoanService : invokes through service contract
    LoanService --> ILoanRepository : depends on
    JsonLoanRepository ..|> ILoanRepository : implements
    JsonLoanRepository --> JsonData : loads and persists

Legend. Rectangles are code types. Solid arrows are dependencies/calls; the dashed realization arrow denotes interface implementation.

Explanation. The diagram describes dependency roles, not proof that every failure branch is tested. Confirm the actual DI registrations and methods in this fixture rather than assuming a generic “clean architecture” template.

Task 3 - Plan and write a useful README

1. In Plan, outline setup, execution directory, architecture, data files, tests, implemented flows, limitations and reset.

2. Require source references for each claim.

3. In Agent, write only the README. Do not “improve” production code during a documentation task.

4. Document this console launch from the copied project:

   cd src/Library.Console
   dotnet run --no-build
   

5. Explain that return/renew operations can modify JSON in the copy; use synthetic records and inspect changes before reset.

Verify your work

• All run commands include their working directory.
• Implemented behavior is separated from future feature ideas.
• The diagram matches actual types and DI registrations.
• Test scope is described without a fabricated coverage percentage.
• Only documentation changed in the exercise diff.

Troubleshooting

If Copilot describes classes it never read, attach and inspect those files. If the console cannot find settings, fix the documented working directory. If the README says all edge cases are covered, ask for the specific test proving each.

Independent practice

Write a troubleshooting entry for a missing JSON file using the real loader behavior. Do not promise graceful recovery when the code throws or merely logs a failure.

Reset

Save the documentation evidence, restore only the exercise README and any JSON records modified by manual exploration, then close the disposable workspace.

Official references

• Context engineering
• Planning
• C# test support