From my Answer for “Run NUnit test on Ubuntu from command line” on Stackoverflow:

Lets start from the beginning:

Get the latest and greatest NUnit AND it’s Runner tools

curl https://api.nuget.org/downloads/nuget.exe -o nuget.exe
mono nuget.exe install NUnit
mono nuget.exe install NUnit.Runners

Make sure the mono is finding those assemblies first (vs the GAC)

export MONO_PATH=$(PWD)/NUnit.Runners.2.6.4/tools;$(PWD)/NUnit.2.6.4/lib

Create your test example (save it to vi OnlyTest.cs):

using System;
using System.Text;
using System.Collections.Generic;
using NUnit.Framework;

[TestFixture]
public class OnlyTest
{
    [Test]
    public void MyTest() 
    {
        int a = 10;
        Assert.AreEqual(10, a);
    }
}

Compile it:

  mcs OnlyTest.cs -target:library -r:NUnit.2.6.4/lib/nunit.framework.dll -out:OnlyTest.dll

Run it:

mono ./NUnit.Runners.2.6.4/tools/nunit-console.exe OnlyTest.dll -noresult

Output:

Using default runtime: v4.0.30319
NUnit-Console version 2.6.4.14350
Copyright (C) 2002-2012 Charlie Poole.
Copyright (C) 2002-2004 James W. Newkirk, Michael C. Two, Alexei A. Vorontsov.
Copyright (C) 2000-2002 Philip Craig.
All Rights Reserved.

Runtime Environment -
   OS Version: Unix 14.3.0.0
  CLR Version: 4.0.30319.17020 ( Mono 4.0 ( 4.3.0 (master/b044a27 Thu Jun 18 15:17:08 PDT 2015) ) )

ProcessModel: Default    DomainUsage: Single
Execution Runtime: mono-4.0
.
Tests run: 1, Errors: 0, Failures: 0, Inconclusive: 0, Time: 0.0280499 seconds
  Not run: 0, Invalid: 0, Ignored: 0, Skipped: 0