create unit tests for all document types

[evgenyigumnov]

Order for tests:

1. Markdown
2. Plain text
3. PDF
4. XLS
5. XLSX
6. CSV
7. ODS
8. Typst
9. RTF
10. DOCX
11. JSON
12. XML

Before create test you should check parser/generate file. for example markdown.rs have already some test. Just move unit test to your file. Integration test do not move