custom_collection_minimal.cs

  class MyObject
  {
      public int Value { get; set; }
  }

  class MyObjectEnumerator
  {
      public bool MoveNext()
      {
          throw new NotImplementedException();
      }
      public MyObject Current { get; }
  }

  class MyCollection
  { 
      public MyObjectEnumerator GetEnumerator()
      {
          throw new NotImplementedException();
      }
  }

  public class Tests
  {
      [Test]
      public void ForEachTest()
      {
          var myCollection = new MyCollection();
          foreach (var element in myCollection)
          {
            // foreach loop works fine :)
          }
      }
  }