Updated source code is here (2012-Jan-28: I forgot to include the Verify Exception in the original source 
)
If you’ve ever used the likes of GTEST for C++ unit testing, you will be familiar with the ASSERT and VERIFY semantics:
- ASSERT – bail out of a test as soon as a condition is false (ie: NULL Pointer)
- VERIFY – acknowledge that a condition is false but continue with the test anyway and get as far as you can. The test still technically failed but more information was gleamed.
Verify is ideal for functional / UI / UAT Automation because it lets the test get as far as it can and elicit as much information as possible before the test completes and a summary of failures are reported: it’s more useful for a developer to know that 5 numeric fields on a form are invalid instead of just one. A colleague pointed out recently that various UI Automation tools tend to implement similar semantics using ‘LogFail’ or similar statements – however, as a developer/tester I find the ‘Verify’ semantics more fitting but they are not part of MsTest.
In this rather long post, I will put Verify into MsTest by wrapping Assert.AreEqual with Verify.AreEqual (for all samples here, this is just an ordinary VS2010 Unit Test). I will provide nothing but a bare-bones implementation here (and I’ve just noticed the code prettifier I use has messed up some of the snippets on this post… please see the source code above for the complete code).
When you do this:
Assert.AreEqual(1,0)
The unit test fails immediately. We want to do this:
Verify.AreEqual(1, 0)
Where the failure is ‘noted’ but the test continues: but when the test completes, if there were verification failures in the test, we need to throw an exception so that the unit testing framework designates the verification failures as a test failure. How to do this in MsTest? There’s a few hurdles to cross!
Syntax
All Assert methods are static. Like so:
Assert.AreEqual(...)
Assertions have no state – a failure is propagated to the test host immediately so static methods are a good fit. Verification failures on the other hand will ‘accumulate’ so we need to preserve state. For this post I have chosen to go the ‘instance’ route so here is a simple Verify class:
public class Verify
{
public Verify()
{
Exceptions = new List();
}
public void AreEqual(int left, int right)
{
...
}
public readonly List Exceptions;
}
However: you can implement Verify methods using thread local storage and static methods but I am trying to keep this long post shorter!
The key is the implementation of the Verify methods: all an Assertion does is throw an exception when a condition is false so all we have to do is sink & record that exception by wrapping it with our Verify calls:
public class Verify
{
....
public void AreEqual(int left, int right)
{
try
{
Assert.AreEqual(left, right);
}
catch(UnitTestAssertException ex)
{
Exceptions.Add(ex);
}
}
}
If the assertion fails; we essentially ‘note’ the failure but continue. Putting it all together, we might have a test like this:
protected Verify Verify;
[TestInitialize]
public void Init()
{
this.Verify = new Verify();
}
[TestMethod]
public void Pointless()
{
Verify.AreEqual(1,2);
Verify.AreEqual(3,3);
Verify.AreEqual(3,4);
}
NOTE: Even though Verification violations occurred, as far as the Unit Testing framework is concerned the test technically passed – no exceptions were thrown by the Unit Test! So we need to check for verification violations in the Cleanup method and then throw our own Exception if Verifications were logged during the test.
When executing that test, we have two Verification errors. But what to do with them? If we are running Pointless with Associated Automation within MTM, we want the test to fail; MTM has no concept of a Warning or a Partial Failure. The test either passes or fails so from MTM’s perspective unit tests should exhibit the same behavior. The Verifications are only useful for troubleshooting, logging and triage so they need to appear in the final log / TRX. If we are running the tests within Visual Studio as a Unit Test, we still need the test to fail for the same reason as above to integrate with the toolchain. How to do this? The easiest place to look for any logged verification failures is in the [TestCleanup] method. If you throw an exception in TestCleanup, the exception/failure is still associated with the Unit Test that has just run (ie: the method containing the Verify methods):
[TestCleanup]
public void Cleanup()
{
if(Verify.Exceptions.Count > 0)
{
throw Verify.Exceptions.First();
}
}
The unfortunate side effect of this is that the exception/stack trace in the Test Results / TRX file looks like it came from Cleanup method and not the test itself. Clicking through takes you to the common Cleanup method which is kind of annoying:
But we can fix that.
CHECKPOINT:We can accumulate verification failures during a unit test and throw an exception in TestCleanup if any verification failures occured. The exception we manually throw could contain a description of every verification encountered so far (for this post: I am dealing with only the first exception and I am keeping message formatting as simple as possible).
But what if the Unit Test contains ASSERTIONS *AND* Verifications? Like so:
[TestMethod]
public void Pointless()
{
Verify.AreEqual(1,2);
Assert.AreEqual(3,3);
Verify.AreEqual(3,4);
}
I have decided that the Assertion gets ‘priority’ – it is that exception/assertion we want to propagate ‘out’ to the unit testing framework. We can determine if a ‘real’ Assertion or Exception was thrown in the Unit Test by looking at the CurrentTestOutcome property:
public TestContext TestContext { get; set; }
[TestCleanup]
public void Cleanup()
{
if(TestContext.CurrentTestOutcome == UnitTestOutcome.Passed)
{
// If we only have Verify failures, as far as MsTest is concerned, the test will pass! So we need to spoof a failure...
if(Verify.Exceptions.Count() > 0)
{
throw Verify.Exceptions.First();
}
}
}
Easy! So we can comfortably mix assertions and verifications in a single functional test and it will “just work” as far as the tool chain is concerned; if a real assertion happens, that one gets propagated. In C++/GTEST, an ASSERT is used to validate a pointer (little need to go on if its NULL…!) and VERIFY is then used for individual properties. In a functional test, an ASSERT might look for a key component of a page; and the VERIFY calls for fields for example. It depends if it fits what you are trying to do. Use your judgement. This will not be suitable in all circumstances.
Fixing the Stack
As stated, if we throw an exception from TestCleanup, the stack trace looks like this:
That’s not good enough! It shows the Cleanup method itself, not the actual line of code where the Verify call was made. Thanks to the .Net designers, this is easy to fix though If you examine System.Exception, you can override two key properties: Message and StackTrace (and there’s a section for each in the TRX file) Yes – as you can override the stack trace text, you can ‘inject’ a stack trace into an exception and fool anything that interprets that exception about its source – such as the TRX viewer. And it’s easy to get the stack trace. Just do this:
string stack = Environment.GetStackTrace();
Trivial! But we will be getting the stack trace in our Verify method… we need to ‘unwind’ a bit. To ‘pop’ a few lines we just do this:
List t = new List(Environment.StackTrace.Split(delims, StringSplitOptions.None));
// 'Pop' a few lines
t.RemoveRange(0, 2);
// Reconstruct
string stack = String.Join("\r\n", t);
With this, we can ‘inject’ a stack trace into our exception. The only way I could find to do this is to create a custom exception class (gives us more flexibility…) and override its virtual StackTrace property. So it makes sense for our new exception to wrap the original exception and delegate every other call to it (where possible):
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Microsoft.VisualStudio.TestTools.UnitTesting;
namespace HaveCompTest
{
// Might as well derive from the unit test exception baseclasses... and you should probably use InnerException : - )
public class MyVerifyWrapperException : UnitTestAssertException
{
// Pass in the original assertion exception
public MyVerifyWrapperException(UnitTestAssertException utex, string spoofedStackTrace)
{
OriginalException = utex;
SpoofedStackTrace = spoofedStackTrace;
}
public override System.Collections.IDictionary Data { get { return this.OriginalException.Data; }}
public override string Message { get { return OriginalException.Message; }}
public override string Source { get { return OriginalException.Source; }}
public override string StackTrace { get { return SpoofedStackTrace; } }
public readonly System.Exception OriginalException;
public readonly string SpoofedStackTrace;
}
}
Getting there! So now when we wrap our original Assert.AreEqual call with our Verify.AreEqual call, we can create our new exception type with the StackTrace we want:
try
{
Assert.AreEqual(left, right);
}
catch(UnitTestAssertException ex)
{
string[] delims = new string[] { "\r\n" };
List t = new List(Environment.StackTrace.Split(delims, StringSplitOptions.None));
// Choose how many lines to strip...
t.RemoveRange(0, 3);
string stack = String.Join("\r\n", t);
// The stack trace now looks like it was thrown directly within the test method itself instead of here.
MyVerifyWrapperException e = new MyVerifyWrapperException(ex, stack);
_Exceptions.Add(e);
}
KOOL! So now when we throw our verify exception in [TestCleanup] like so, in the TRX viewer we see this:
Clicking through takes us straight to the location of the Verify failure.
DONE!
Putting it all together
The source code for a simple skeleton class can be found here (just add it to an ordinary MsTest Unit Test).
Tips
You’ll need to wrap all the Assert.XXX calls… a delegate is your friend when doing this… () => { Assert.AreEquals(…) }
The error message says ‘Assert.’ in TRX. Modify the ErrorMessage in MyVerifyWrapperException to say Verify…
You might want a clickthrough to all Verifications in the Stack Trace view…
If mixed Assertion / Verification failures occur within a test, you might still want the Verifications to show up in TRX…
Use Thread Local Storage to implement static Verify syntax so they are similar to Assert…
