<p>I've used NUnit for years and I wanted to try XUnit.  So I installed XUnit and ran the executable that allowed you to run XUnit via TD.net.  </p>

<p>I can't seem to run more than one test at a time. With NUnit + TD.net, I could click on the filename in the solution and run all the tests in the file.  I can't seem to do that with XUnit + TD.net. </p>

<p>Is this something I can do?</p>

Short Answer: Copy the following into a .reg file on your computer, updating the path to where your Xunit dll resides, and then import it into your registry.
Windows Registry Editor Version 5.00
[HKEY_LOCAL_MACHINE\SOFTWARE\MutantDesign\TestDriven.NET\TestRunners\xunit] @="4"
  "AssemblyPath"="C:\_Files\Programs\Programming\XUnit\xunit-1.1.0\xunit.runner.tdnet.dll"
  "TypeName"="Xunit.Runner.TdNet.TdNetRunner"
Long Answer:
I've run into this problem a couple of times, both on 32 and 64 bit versions of windows. TestDriven.net uses the registry to store a list of test frameworks avaialable. XUnit comes with an installer xunit.installer (run as admin) which is supposed to make the correct registry entries.
Usually I can get TD.net to work with XUnit for awhile, then I loose support. Today I was trying to get it to work on Windows 7 beta for the first time and couldn't get it to work at all.
After some searching I found the registry key that the information about the test framework should be entered in.
HKEY_LOCAL_MACHINE\SOFTWARE\MutantDesign\TestDriven.NET\TestRunners
Now on 64bit systems, there is also a key under the Wow6432Node, which is where it looks like the Xunit installer was setting the registry key.
Anyway, I exported the the the xunit registry key from HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\MutantDesign\TestDriven.NET\TestRunners\xunit and, edited it, removing the Wow6432Node and then imported it. After restarting visual studio, everything works. I'll keep the registry file around in case it breaks again.