title: NSubstitute -3.x 'ValueType' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard,
body: <p>I am struggling to find a reason behind this error in my code:</p>
  
  <blockquote>
    <p>ApplicationServiceTests\Test.cs(29, 13): error CS0012: The
    type 'ValueType' is defined in an assembly that is not referenced. You
    must add a reference to assembly 'netstandard, Version=2.0.0.0,
    Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.</p>
  </blockquote>
  
  <p>The code line is:</p>
  
  <pre><code>        repo.GetCoveredCards(Arg.Is(cifCode)).Returns(Task.FromResult(new GetCustomerCCPlusResponse()
          {
              CreditCardPlus = new[] { card1, card2 }
          }));
  </code></pre>
  
  <p>Tools, framework and Package</p>
  
  <p>.net framework 4.6.1
  Visual Studio 2015 using MSBuild 14.
  NSubstitute 3.1.0 </p>
  
  <p>It seems like when I use NSubstitute version 1.10.0 and it has worked really well. </p>
  
  <p>Now the question is why am I getting this error with the latest version of NSubstitute?</p>