Assert in Try..Catch block is caught

Question

Just came across some interesting behavior - Assert being caught by Catch block.

List<Decimal> consArray = new List<decimal>();
try
{
    Decimal d;
    Assert.IsTrue(Decimal.TryParse(item.Value, out d));
    consArray.Add(d);
}
catch (Exception e)
{
     Console.WriteLine(item.Value);
     Console.WriteLine(e);
}

Assert throws AssertFailedException and its caught by catch . Always thought that if Assert fails then test is failed and consecutive execution is aborted. But in that case - test moves along. If nothing wrong happens later - I get green test! In theory - is it right behavior?

Edited: I understand that maybe it is .NET restriction and how asserts are made in MsTest. Assert throws exception. Since catch - catches everything it catches assert exception. But is it right in theory or MsTest specific?

Answer 1

As already answered, this is correct behavior. You can change your code to get Your expected behavior by catching the AssertFailedException and re-throwing it.

        List<Decimal> consArray = new List<decimal>();
        try
        {
            Decimal d;
            Assert.IsTrue(Decimal.TryParse(item.Value, out d));
            consArray.Add(d);
        }
        catch (AssertFailedException)
        {
            throw;
        }

        catch (Exception e)
        {
            Console.WriteLine(item.Value);
            Console.WriteLine(e);
        }

Answer 2

Your code is working as expected. When an Assert fails it throws an AssertFailedException which inherits from Exception . So you can add a try-catch and catch it.

In your case, add a throw at the end of the catch and re-throw the exception.

Answer 3

NUnit will do the exact same thing. As should any other test framework I think, but I only know MStest and NUnit in C#.

I'd expect that your test code would not contain Decimal.TryParse , but your business logic would do that, which you'd test with an object and a method call.

Something like:

var sut = new Sut();
var d = sut.DoSomethingThatReturnsTheDecimal(item.Value);

Assert.AreEqual(0.123, d, string.Format("passed value can not be parsed to decimal ({0})", item.Value);

In order to stay a bit closer to your implementation:

List<Decimal> consArray = new List<decimal>();

Decimal d = Decimal.MinValue;

// You don't need to try-catch a Decimal.TryParse
// Decimal.TryParse(item.Value, out d));

try
{
    d = Decimal.Parse(item.Value)
}
catch
{
    // Handle exception
}

Assert.AreEqual(0.123, d);

// Does the list add anything at all? In this sample it seems a bit redundant
consArray.Add(d);

Anyway, to answer your question. The try-catch is supposed to catch your AssertFailedException .

PS: Catching the AsserFailedException and re-throwing it will also work, but it feels a bit strange to me. I'd strive to leave the Assert s outside any try-catch blocks. But that might be just my opinion which you didn't ask for :).