var result = WaitFor.For(() => 0)
                .Become(a => a == 5)
                .OnFailure(_ => 1, fail => fail is NotExpectedValue<int>)
                .OnFailure(_ => -2);
                
 //asynchronous option         
  var result = WaitFor.ForAsync(async () =>
     {
         await Task.Delay(10);
         return 0;
     })
     .Become(a => a == 5)
     .OnFailure(_ => 1, fail => fail is NotExpectedValue<int>)
     .OnFailure(_ => -2);                

Using the OnSuccess method, you can specify actions on the value in case of a successful result

var res = WaitFor.For(() => actual).Become(a => a == 3)
              .OnSuccess(x => $"New result {x}")
              .OnFailureThrowException();
// "New result 3"

Result On Failure can be in two cases:

• get not expected value
  • returns NotExpectedValue<T> type.
• due to some exceptions
  • returns ExceptionsHappened type.

We have methods that can help to handle these cases:

• WhenNotExpectedValue and DoWhenNotExpectedValue
• WhenWasExceptions and DoWhenWasExceptions

 var res = WaitFor.For(() => 3)
               .Become(a => a == 4)
               .WhenNotExpectedValue(x => x.ActuallyValue)
               .OnFailure(_ => 0);
Console.WriteLine(res) //3

 WaitFor.For(() => 3)
               .Become(a => a == 4)
               .DoWhenNotExpectedValue(x => Console.WriteLine(x))
               .OnFailure(_ => 0);
//  Console output :
//  Timeout after 30.6826992 second(s) and NUMBER OF ATTEMPTS 17 
//  Expected: (a) => a == 4, but parameter 'a': 3

var testClass = new SomeClass
{
    SomeNumber = 3,
    Child = new OtherClass
    {
       SomeNumber = 5
    }
};

_ = WaitFor.For(() => testClass)
     .Become(a => a.Child.SomeNumber == 1 && a.SomeNumber == 3)
     .DoWhenNotExpectedValue(x => Console.WriteLine(x));
/*  Console output :      
   Timeout after 30.6749663 second(s) and NUMBER OF ATTEMPTS 17 
   Expected: (a) => a.Child.SomeNumber(5) == 1 && a.SomeNumber(3) == 3
*/

If you use OnFailureThrowException , exception will be throw with next message

await WaitFor.ForAsync(Expected)
              .Become(a => a.Child.SomeNumber == 1 && a.SomeNumber == 3)
              .OnFailureThrowException();

You can use the predefined algorithm like LogarithmStep and ParabolaStep which calculate delay steps

var res = WaitFor.For(() => actual,
                  w => w.SetLogarithmStep(Time.FromSeconds).Build())
                 .Become(a => a == 3)
                 .OnFailureThrowException();

Also, you can use your custom algorithm for delayed steps

var res = WaitFor.For(() => actual, 
                      b => b.SetTimeBetweenStep(retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)))
                     .Build())
                     .Become(a => a == 5);

For additional information look in Tests Cases