Before:
  source ../after/ftplugin/markdown.vim

After:
  setlocal foldexpr=0
  setlocal foldmethod=manual

Given markdown;
# Title

## Chapter 1

```
This is code block
# This is just a comment
```

## Capter 2

foobar

Execute (fold level # in code block):
  AssertEqual foldlevel(1), 0, '# Title'
  AssertEqual foldlevel(3), 1, '## Chapter 1'
  AssertEqual foldlevel(7), 2, '# This is just a comment'
  AssertEqual foldlevel(8), 2, '```'
  AssertEqual foldlevel(10), 1, '## Chapter 2'
  AssertEqual foldlevel(12), 2, 'foobar'

Given markdown;

==+ Fold Level 1

--+ Fold Level 2

Execute (fold level ==+, --+):
  AssertEqual foldlevel(2), 1, '==+'
  AssertEqual foldlevel(4), 2, '--+'