TestProgram.cs

[TestFixture]
public class TestProgram
{
    private string expectedText = "Expected text";
    private string initialText = "Initial text"; 

    [Test]
    public void TestChangeValue()
    {
        var mySample = new SampleClass(initialText);

        Program.ChangeValue(mySample, expectedText);
        Assert.AreEqual(expectedText, mySample.Value); 
    }

    [Test]
    public void TestChangeValueRef()
    {
        var mySample = new SampleClass(initialText);

        Program.ChangeValue(ref mySample, expectedText);
        Assert.AreEqual(expectedText, mySample.Value);
    }

    [Test]
    public void TestInit()
    {
        var mySample = new SampleClass(initialText);

        Program.InitValue(mySample, expectedText);
        Assert.AreEqual(expectedText, mySample.Value);
    }

    [Test]
    public void TestInitRef()
    {
        var mySample = new SampleClass(initialText);

        Program.InitValue(ref mySample, expectedText);
        Assert.AreEqual(expectedText, mySample.Value);
    }
}