```ruby
    ret = backend.run_command(backend.commands.check_file_md5checksum(file, pattern))
    ret[:exit_status] == 0
```

This should be like this:

```ruby
    backend.check_file_md5checksum(example, file, pattern)
```

Here, ``method_missing`` is called because ``check_file_md5checksum`` is not implemented in Backend::Exec.
https://github.com/mizzy/serverspec/blob/master/lib/serverspec/backend/exec.rb#L32

And ``method_missing`` runs ``commands.check_file_md5checksum(file, pattern)`` and check its return code.