You can also use GitHub “fenced” syntax like:

```
iex> MyProject.subtract(10, 5) == 5
true
```

In the docs. That is why doctest looks for any line that starts with iex>.

I’m not sure if this’ll fix the issue, but I believe you’re supposed to indent 4 spaces for doc tests. This has to do with markdown formatting, where it’s not seen as a code block unless it is indented or has code fences (three backticks).

So:

  @doc """
  Function 'subtract' takes 2 args and returns answer.

  ## Example

      iex> MyProject.subtract(10, 5) == 5
      true
  """

  def subtract(a, b) do
    a - b
  end

OK, I did indeed shift the actual example iex> stuff 4 ‘further spaces’ indented.
Now it works…

Nice one but still leaves me baffled as to why I got clean builds with incorrect formatting ?

Many thanks anyway.