File
This field can a contain single testable file or multiple testable files. You can choose to input each file or you can choose to use a pattern that matches testable files. In order to match multiple files using patterns, you will need to put the pattern in Ant Pattern format. Each file/pattern must be on its own line.
Output file
When NUnit executes, the output will be stored in this file. Even when specifying multiple files to test, all of the output it put into a single file.
Project configuration
If you've specified a Visual Studio or NUnit project then you can specify the configuration you want to test against. For example, Debug, Release, etc...
Text Fixture
If you want to test a certain fixture, enter it here. If you leave this input empty it will test every fixture.
.NET Framework
Select the .NET framework to run the tests under.
Fail action if any tests fail
If any tests fail the build will be stopped and marked as failed. This option isn't applied to tests that have any errors. If a test errors then the build is stopped and marked as errored regardless of this option.
Using
The Using drop down is populated with any property collector whose namespace matches the pattern defined by the NUnit Action. The pattern for this action is ^NUnit.*
If you create a property collector for this action, make sure you select the Path Finder PlugIn type and give it a name that will match the pattern above in blue. Example names listed here, search the table's Plugin column for "NUnit".
For more in-depth explanations on property collectors see Managing Property Collectors.
Alternatively, you can select the Custom option from the Using drop down list and specify a path in the resulting input field that will be displayed. Please read Why it's a good idea to use a property collector before using this option.