Retry on exception in a try catch block

Question

I'm trying to replicate a scenario where the code should rerun a certain number of times if an exception is caught.

using System;
using System.Threading;

public class Program
{
    public static void Main()
    {
        MyClass myClass = new MyClass();
        Console.WriteLine(myClass.MyMethod(5));
    }
}

public class MyClass
{
    public Test(){}

    public string MyMethod(int tryCount) {          
        while(tryCount > 0)
        {
            // some logic that returns the switchType
            // in this case i'm just manually setting it to 1       
            int switchType = 1;

            try {
                switch(switchType)
                {
                    case 1:
                        return "it worked!!!";
                    case 2:
                        break;
                }
            } catch (Exception e){
                if (--tryCount == 0) throw new Exception("Failed");
            }
        }

        return null;
    }
}

How do I force it to go the catch block, so that I can test my re-try logic is working?

Not really, since in my case, for the sake of testing, I want to force an exception. — blankface, May 08 '20 at 06:14
It's probably in the code that produces `switchType` than you want to catch, no? — vc 74, May 08 '20 at 06:19
There is no way, simple `switch` with `int`s will throw exception... therefore there is no way, or reason to test it. If you had something that could throw exception (eg. `someClass.DoSomething()`).. then you could mock that part (eg. `someClassMock.Setup(mock => mock.DoSomething()).throws(new Exception())`) — Šimon Kocúrek, May 08 '20 at 06:20
@vc74 That makes sense, I'll flesh it out to trigger an exception. Besides that is my retry logic sound? — blankface, May 08 '20 at 06:22

score 1 · Accepted Answer · answered May 08 '20 at 06:27

The shortest answer to your question is "just throw a new exception".

But you probably want to be able to test Happy Path too.

Here's what I'd do:

using System;
using System.Threading;

public class Program
{
    public static void Main()
    {
        // what happens when no problem
        MyClass.happyPath = true;
        MyClass myClass = new MyClass();
        Console.WriteLine(myClass.MyMethod(5));

        // does the retry work?
        MyClass.happyPath = false;
        MyClass myClass = new MyClass();
        Console.WriteLine(myClass.MyMethod(5));
    }
}

public class MyClass
{

    public static boolean happyPath = true; 

    public Test(){}

    public string MyMethod(int tryCount) {          
        while(tryCount > 0)
        {
            // some logic that returns the switchType
            // in this case i'm just manually setting it to 1       
            int switchType = 1;

            try {
                switch(switchType)
                {
                    case 1:

                        if (!happyPath) {
                           throw new Exception ("Oops, it didn't work!");
                        }
                        return "it worked!!!";
            case 2:
                        break;
                }
            } catch (Exception e){
                if (--tryCount == 0) throw new Exception("Failed");
            }
        }

        return null;
    }

}

The throw that you add inside the break statement should be caught by your catch which allows you to check out your retry logic. Suggest you add some logging.

This is exactly what I was looking for. Thanks. On another note, does my re-try logic look sound to you? — blankface, May 08 '20 at 06:31

score 0 · Answer 2 · answered May 08 '20 at 06:24

0

You can throw exception from your code manually while testing.

throw new Exception("Your custom message");

answered May 08 '20 at 06:24

Vidya Sangle

29
5

Retry on exception in a try catch block

2 Answers2