.net – Unit test fails, tested code works!

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I have a simple unit test which tests that a validation function picks up a specific validation issue. The validation item returns a simple object with Item & Message properties. I've written a unit test for this function but this always fails even though I know the function works as expected.

<TestMethod()> Public Sub ContractNote_ValidateForManualInputTest_TradeOrderValueComparison()

    'Can't get this test to work even though validation works!
    Dim CN As ContractNote = New ContractNote
    Dim Trade As New TradeOrder

    Trade.TradeValue = 100

    With CN
        .CNTradeDate = Date.Today
        .CNTradePrice = 1
        .CNTradeUnits = 1
        .CNTradeValue = 1
        .FundManagerReference = "_zzz_"
        .SkandiaCompanyOrderID = "xxx"
        .ParentTradeOrder = Trade
    End With

    Dim ActualItems As System.Collections.Generic.List(Of ValidationItem) =       CN.ValidateForManualInput  

    If actualitems.Count > 0 Then             
        Dim item As ValidationItem = New ValidationItem("Value", "Must match trade value")
        CollectionAssert.Contains(ActualItems, item, "")
    End If

    Assert.AreNotEqual(0, ActualItems.Count)

End Sub

I've implemented IComparable on ValidationItem (I have a separate unit test which confirms this works). Am I Using CollectionAssert correctly?

Best Solution

The MSDN doc for CollectionAssert.Contains(collection,element,message) says:

Verifies that the specified collection contains the specified element. The assertion fails if the element is not found in the collection. Displays a message if the assertion fails.

Assuming CN.ValidateForManualInput returns a List of ValidationItems in ActualItems, let me call those items "A", "B" and "C" for a moment.

Next you create a new ValidationItem, constructing it with "Value" and "Must match trade value". Let me call this new ValidationItem "D" for a moment.

I think that your problem may be that your call to CollectionAssert.Contains() effectively says:

Assert that D is in the list that has only 3 items in it, A, B and C.

But it isn't, so the test fails.

What if, instead of CollectionInsert.Contains(), you loop over all the items in ActualItems and check each with something like:

Assert (ActualItems[ii].message is Not "Must match trade value")

(That may not be exact VB syntax. I usually write C#.)

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How should I unit test multithreaded code

Look, there's no easy way to do this. I'm working on a project that is inherently multithreaded. Events come in from the operating system and I have to process them concurrently.

The simplest way to deal with testing complex, multithreaded application code is this: If it's too complex to test, you're doing it wrong. If you have a single instance that has multiple threads acting upon it, and you can't test situations where these threads step all over each other, then your design needs to be redone. It's both as simple and as complex as this.

There are many ways to program for multithreading that avoids threads running through instances at the same time. The simplest is to make all your objects immutable. Of course, that's not usually possible. So you have to identify those places in your design where threads interact with the same instance and reduce the number of those places. By doing this, you isolate a few classes where multithreading actually occurs, reducing the overall complexity of testing your system.

But you have to realize that even by doing this, you still can't test every situation where two threads step on each other. To do that, you'd have to run two threads concurrently in the same test, then control exactly what lines they are executing at any given moment. The best you can do is simulate this situation. But this might require you to code specifically for testing, and that's at best a half step towards a true solution.

Probably the best way to test code for threading issues is through static analysis of the code. If your threaded code doesn't follow a finite set of thread safe patterns, then you might have a problem. I believe Code Analysis in VS does contain some knowledge of threading, but probably not much.

Look, as things stand currently (and probably will stand for a good time to come), the best way to test multithreaded apps is to reduce the complexity of threaded code as much as possible. Minimize areas where threads interact, test as best as possible, and use code analysis to identify danger areas.

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Best Solution

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