Comparing two instances of a class

You should implement the IEquatable<T> interface on your class, which will allow you to define your equality-logic.
Actually, you should override the Equals method as well.

public class TestData : IEquatable<TestData>
{
   public string Name {get;set;}
   public string type {get;set;}

   public List<string> Members = new List<string>();

   public void AddMembers(string[] members)
   {
      Members.AddRange(members);
   }   

  // Overriding Equals member method, which will call the IEquatable implementation
  // if appropriate.

   public override bool Equals( Object obj )
   {
       var other = obj as TestData;
       if( other == null ) return false;

       return Equals (other);             
   }

   public override int GetHashCode()
   {
      // Provide own implementation
   }


   // This is the method that must be implemented to conform to the 
   // IEquatable contract

   public bool Equals( TestData other )
   {
       if( other == null )
       {
            return false;
       }

       if( ReferenceEquals (this, other) )
       {
            return true;
       }

       // You can also use a specific StringComparer instead of EqualityComparer<string>
       // Check out the specific implementations (StringComparer.CurrentCulture, e.a.).
       if( EqualityComparer<string>.Default.Compare (Name, other.Name) == false )
       {
           return false;
       }
       ...

       // To compare the members array, you could perhaps use the 
       // [SequenceEquals][2] method.  But, be aware that [] {"a", "b"} will not
       // be considerd equal as [] {"b", "a"}

       return true;

   }

}