Project · Interview practice

Stock decision review harness

Twelve independent boundary and contract checks around pure checked stock decisions, without external storage.

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All C# source files below are loaded together in the playground. Files written by a run live in its virtual directory.

Interview.csproj

<Project Sdk="Microsoft.NET.Sdk"><PropertyGroup><OutputType>Exe</OutputType><TargetFramework>net9.0</TargetFramework><LangVersion>13.0</LangVersion><ImplicitUsings>enable</ImplicitUsings><Nullable>enable</Nullable></PropertyGroup></Project>

Program.cs

Console.WriteLine(ReviewChecks.Run()+" stock review checks passed");

Domain/StockRules.cs

public sealed record StockInput(int Available,int Quantity,long PriceCents);
public sealed record StockDecision(string Status,long Total);
public static class StockRules {
    public static StockDecision Decide(StockInput value) {
        if(value.Available<0 || value.Quantity<=0 || value.PriceCents<0) return new("invalid",0);
        if(value.Quantity>value.Available) return new("insufficient",0);
        return new("accepted",checked(value.Quantity*value.PriceCents));
    }
}

Checks/ReviewChecks.cs

public static class ReviewChecks {
    public static int Run() {
        int count=0; void Check(bool ok,string name){if(!ok)throw new InvalidOperationException(name);count++;}
        Check(StockRules.Decide(new(4,2,150))==new StockDecision("accepted",300),"ordinary");
        Check(StockRules.Decide(new(4,4,150)).Total==600,"exact stock");
        Check(StockRules.Decide(new(4,5,150)).Status=="insufficient","over stock");
        Check(StockRules.Decide(new(4,0,150)).Status=="invalid","zero");
        Check(StockRules.Decide(new(4,-1,150)).Status=="invalid","negative quantity");
        Check(StockRules.Decide(new(-1,1,150)).Status=="invalid","negative stock");
        Check(StockRules.Decide(new(4,1,-1)).Status=="invalid","negative price");
        Check(StockRules.Decide(new(1,1,0))==new StockDecision("accepted",0),"free valid");
        Check(StockRules.Decide(new(2,2,int.MaxValue)).Total==4294967294L,"wide multiply");
        bool overflow=false;try{StockRules.Decide(new(2,2,long.MaxValue));}catch(OverflowException){overflow=true;} Check(overflow,"overflow");
        var input=new StockInput(3,2,10);_ = StockRules.Decide(input);Check(input==new StockInput(3,2,10),"input unchanged");
        Check(StockRules.Decide(new(-1,0,-1)).Status=="invalid","precedence");return count;
    }
}