tests: Add test for unescaping "\\n" in step4
tests: Add test for unescaping "\\n" in step4

Several implementations fail when unescaping "\\n" in their reader
module because string-wide replacements of the two chars '\' and 'n' by
a newline char will replace the last two chars.

foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal,foresterre/mal