This may look like a hack but the resulting error message is really nice:
```
     ** (ExUnit.ExpectationError)
       expected doctest: inspect (HashDict.new a: 0, b: 1, c: 2)
         to evaluate to: "#HashDict<[a: 0, b: 1, c: 2]>"
            instead got: "#HashDict<[d: 3, e: 4, f: 5]>"
```

You see exactly what is happening.