At the moment the easiest way is to just Exec it.
<Target Name="RunSpecs">
<PropertyGroup>
<MSpecCommand>
lib\machine\specifications\Machine.Specifications.ConsoleRunner.exe $(AdditionalSettings) path\to\your\project\bin\Debug\Your.Project.Specs.dll path\to\your\other\project\bin\Debug\Your.Other.Project.dll
</MSpecCommand>
</PropertyGroup>
<Message Importance="high" Text="Running Specs with this command: $(MSpecCommand)"/>
<Exec Command="$(MSpecCommand)" />
</Target>
Edit: Notice Additional Settings, you can call into the target like this:
<MSBuild Projects="yourmsbuild.msbuild" Targets="RunSpecs" Properties="AdditionalSettings=-s -t -i "web" --html Specs\Specs.html"/>
If you pass --teamcity as an argument it outputs teamcity specific log data so TeamCity will track your tests.
Machine.Specifications
Copyright (C) 2007, 2008
Usage: mspec-runner.exe [options] <assemblies>
Options:
-i, --include Executes all specifications in contexts with these comma delimited tags. Ex. -i "foo,bar,foo_bar"
-x, --exclude Exclude specifications in contexts with these comma delimited tags. Ex. -x "foo,bar,foo_bar"
-t, --timeinfo Shows time-related information in HTML output
-s, --silent Suppress console output
--teamcity Reporting for TeamCity CI integration.
--html <PATH> Outputs an HTML file(s) to path, one-per-assembly w/ index.html (if directory, otherwise all are in
one file)
-h, --help Shows this help message