Given markdown;
# a

Execute (Toc does not set nomodifiable on other files):
  " Sanity check.
  Assert &modifiable

  :Toc
  :lclose
  :edit a

  Assert &modifiable

Given markdown;
header 1
========

test

header 2
--------

test

### header 3

test

Execute (Toc setex headers):
  :Toc

Expect (setex headers):
  header 1
    header 2
      header 3

Given markdown;
# header 1

test

## header 2

test

### header 3

test

Execute (Toc atx headers):
  :Toc

Expect (atx headers):
  header 1
    header 2
      header 3