What is the output of that code snippet?
Console.Write(new Derived("Test"));

public abstract record Base(string Key)
{
    public override string ToString() => Key;
}

public sealed record DerivedRecord(string Key) : Base(Key);
Probably "Test"?

We Are .NET

A C# gotcha: when a base record overrides ToString(), the derived record compiler-generates its own ToString() that ignores the base implementation, producing output like 'DerivedRecord { Key = Test }' instead of just 'Test'. The fix, introduced in C# 10, is to mark the base record's ToString() override as sealed, preventing the compiler from regenerating it in derived records.

records ToString and inheritence