System.MissingMethodException: Method not found: 'System.IO.Compression.ZipArchive System.IO.Compression.ZipFile.Open(System.String, System.IO.Compression.ZipArchiveMode)'.
    at UnitTestProject.UnitTest1.TestMethod1()

using System.IO.Compression;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace UnitTestProject
{
    [TestClass]
    public class UnitTest1
    {
        [TestMethod]
        public void TestMethod1()
        {
            string zipfilename = "C:\temp\out.zip";
            using (ZipArchive zipArchive = ZipFile.Open(zipfilename, ZipArchiveMode.Read)) { }
        }
    }

namespace StandardClassLib
{
    public static class Zipper
    { // Class is empty.
    }
}