User Mode Monitor

The User Mode Monitor allows tests to obtain more context about the execution of the 'process under test' in order to obtain more context for investigating test failures, or for enabling better verification from existing tests. The current User Mode Monitor implementation provides a basic implementation, with more customization and configuration coming in subsequent releases.


The User Mode Monitor (UMM) uses low-level Windows API's to be notified of all 'debugger' events that originate from a given process - thread start and stop, module load, crashes, and handled exceptions to name just a few. Upon receiving a debugger event the UMM code can take one of several actions, including logging comments, logging errors (in order to fail a test), or even taking a minidump of the Process Under Test.

Enabling the User Mode Monitor

To enable the UMM for a given test case, you need to provide two pieces of configuration:

  1. The test must be marked with the 'ProcessUnderTest' metadata value. This allows the UMM to identify the process that is being tested.
  2. The Te.exe command line should include '/userModeMonitor' to turn on the UMM functionality.

The following points should be taken into account when using the UMM code;

  1. If there are multiple instances of the named Process Under Test running, then the instance that is discovered first will be used.
  2. The user that is executing the test automation must have sufficient permission to receive debugger events from the Process Under Test.
  3. The UMM code will 'attach' to the Process Under Test after the all setup fixtures have executed, and 'detach' before cleanup fixtures are executed. This allows a test's setup fixtures to start the Process Under Test, and perform any necessary initialization to prepare for the test.

Supported User Mode Monitor 'Actions'

The User Mode Monitor has a set of 'Actions' that it can take when a given debugger event occurs in the monitored process. In the current implementation, a given event will only invoke it's default action; there is currently no configuration support.

Action Description
LogComment Adds a comment to the log, with contextual information from the event.
LogError Logs an error to the log, which will fail the current test.
Minidump Writes out a minidump and saves it to the Log.
Ignore Does nothing.

Supported User Mode Monitor 'Events'

The User Mode Monitor surfaces 'events' that can apply one of the 'actions' that are listed, above. The following table shows the current list of reported events, along with the default Action that will be performed when the event is received.

Event Default Action (second chance default action)
Create thread Ignore
Exit thread Ignore
Create process Ignore
Exit process LogError
Load module LogComment
Unload module Ignore
System error Ignore
Initial breakpoint LogError
Initial module load Ignore
Debuggee output LogComment
Access violation LogError (LogError)
Assertion failure LogError (LogError)
Application hang LogError (LogError)
Break instruction exception LogError
Break instruction exception continue Ignore
C++ EH exception LogError (LogError)
CLR exception LogError (LogError)
CLR notification exception LogError (Ignore)
Control-LogError exception LogError
Control-LogError exception continue Ignore
Control-C exception LogError
Control-C exception continue Ignore
Data misaligned LogError (LogError)
Debugger command exception Ignore
Guard page violation LogError (LogError)
Illegal instruction LogError (LogError)
In-page I/O error LogError (LogError)
Integer divide-by-zero LogError (LogError)
Integer overflow LogError (LogError)
Invalid handle LogError
Invalid handle continue LogError
Invalid lock sequence LogError (LogError)
Invalid system call LogError (LogError)
Port disconnected LogError (LogError)
Service hang LogError (LogError)
Single step exception LogError
Single step exception continue Ignore
Stack buffer overflow LogError (LogError)
Stack overflow LogError (LogError)
Verifier stop LogError (LogError)
Visual C++ exception Ignore (Ignore)
Wake debugger LogError (LogError)
WOW64 breakpoint LogError (Ignore)
WOW64 single step exception LogError (Ignore)
Other exception LogError (LogError)


In order to illustrate the use of the UMM functionality, let's take a look at a (slightly contrived) example of a test that automates 'MSPaint':

namespace UserModeMonitorExample
    using System;
    using System.Diagnostics;
    using System.Threading;
    using Microsoft.VisualStudio.TestTools.UnitTesting;
    using WEX.Logging.Interop;
    using WEX.TestExecution;

    public class BasicExample
        public void TestInitialize()
            Process[] runningPaintInstances = Process.GetProcessesByName("mspaint.exe");

            Verify.IsTrue(runningPaintInstances.Length == 0, "There are no running instances of mspaint.exe");

            this.mspaintUnderTest = Process.Start("mspaint.exe");

        public void TestCleanup()
            // Close the 'mspaint under test' - if it's already gone, this will throw, but that's no big deal.

        [TestProperty("ProcessUnderTest", "mspaint.exe")]
        [TestProperty("Description", "Shows how a test can be failed if the UI is closed from underneath the test.")]
        public void SimpleInteraction()
            Log.Comment("If the 'user mode monitor' is enabled and mspaint.exe is closed,");
            Log.Comment("then this test will be failed.");
            Log.Comment("Sleeping for 5 seconds");


        private Process mspaintUnderTest;

Here's a quick breakdown of the structure of the test:

  • The 'SimpleInteraction' test represents a test that interacts with a UI based application - in this case it's "MSPaint.exe". Notice, that the "ProcessUnderTest" metadata has been applied to call out that this test is testing the "mspaint.exe" process.
  • The test has a setup fixture that makes sure that there's no pre-existing instances running, and launches a single instance to test.
  • The test also has a cleanup fixture that closes the instance that was launched in the setup fixture.

The 'test' is very straight forward, let's look at possible outcomes:

  1. The test runs without problems. This is the best possible outcome.
  2. Without UMM enabled, a user closes the MSPaint instance during execution. In this case, the test will pass, but the cleanup will fail with an 'InvalidOperationException'.
  3. With UMM enabled, a user closes the MSPaint instance during execution. In this case, the UMM code will log an error showing that the process closed failing the test. The cleanup fails as in case (2).

With UMM enabled, the errant behavior is reported immediately, and directly affects the test result. This is a much better testing pattern since errors are reported as early as possible and extra context is provided to help with debugging or understanding test failures.

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