Here is a code snippet for typing "nunit" and have it give a template using NUnitLite:

<?xml version="1.0" encoding="utf-8"?>
<CodeSnippets xmlns="http://schemas.microsoft.com/VisualStudio/2005/CodeSnippet">
<CodeSnippet Format="1.0.0">
<Header>
<Title>nunit</Title>
<Description>nunit - assemblies and namespaces</Description>
<Shortcut>nunit</Shortcut>
<SnippetTypes>
<SnippetType>Expansion</SnippetType>
</SnippetTypes>
</Header>
<Snippet>
<References>
<Reference>
<Assembly>nuget:NUnitLite</Assembly>
</Reference>
</References>
<Imports>
<Import>
<Namespace>NUnit.Framework</Namespace>
<Namespace>NUnit.Options</Namespace>
<Namespace>NUnitLite</Namespace>
</Import>
</Imports>
<Declarations>
<Literal>
<ID>TestName</ID>
<Default>WhenXShould</Default>
</Literal>
</Declarations>
<Code Language="csharp"><![CDATA[void Main()
{
new AutoRun().Execute(new[]{"--noheader","--noresult"});
}

[TestFixture]
public class TestHarness
{
// Write your tests here
[TestCase("scenario", 0)]
public void $TestName$(string scenario, int expectedValue)
{
// setup

// execute
var actual = 0;

// verify
Assert.That(actual, Is.EqualTo(expectedValue), scenario);
}

}]]></Code>
</Snippet>
</CodeSnippet>
</CodeSnippets>

If you use NUnitLite 3.0, you'll need to call it this way:

NUnitLite in 3.0 uses the following format,

public static void Main(string[] args)
{
new AutoRun().Execute(args);
}

See

https://groups.google.com/forum/#!topic/nunit-discuss/AU7ZX0v8ToQ

I use NUnit Lite to write and execute tests in LINQPad.

http://scriptbucket.wordpress.com/2014/03/16/how-to-unit-test-a-linqpad-code-snippet/

Damn you read my mind, with the exception of having growl notifications so as to not wait for test completion.

or perhaps MSTest =)