Add tests for tab width.

src/compare/parse.rs

@@ -7,10 +7,12 @@ use crate::GlobalSettings;
 ///
 /// Currently only org-list-allow-alphabetical is supported.
 fn global_settings_elisp(global_settings: &GlobalSettings) -> String {
+    // This string concatenation is wildly inefficient but its only called in tests 🤷.
     let mut ret = "".to_owned();
     if global_settings.list_allow_alphabetical {
         ret += "(setq org-list-allow-alphabetical t)\n"
     }
+    ret += format!("(setq-default tab-width {})", global_settings.tab_width).as_str();
     ret
 }