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Harden ListBooks() against external mutation by returning a defensive copy #1

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Merged
askrinnik merged 2 commits into from
May 14, 2026
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Harden ListBooks() against external mutation by returning a defensive copy #1

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d6ab7bb
Initial plan
Copilot May 14, 2026
1915587
fix(book-app-cs): return copy from ListBooks and test immutability
Copilot May 14, 2026
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2 changes: 1 addition & 1 deletion samples/book-app-project-cs/Services/BookCollection.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,7 @@ public Book AddBook(string title, string author, int year)
return book;
}

public List<Book> ListBooks() => _books;
public List<Book> ListBooks() => _books.ToList();

public Book? FindBookByTitle(string title)
{
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10 changes: 10 additions & 0 deletions samples/book-app-project-cs/Tests/BookCollectionTests.cs
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Expand Up @@ -68,6 +68,16 @@ public void RemoveBook_NonexistentBook_ShouldReturnFalse()
Assert.False(result);
}

[Fact]
public void ListBooks_ShouldReturnCopy_AndPreventExternalMutation()
{
_collection.AddBook("Dune", "Frank Herbert", 1965);
var books = _collection.ListBooks();
books.Clear();

Assert.Single(_collection.Books);
}

// --- FindByAuthor ---

[Fact]
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