Write tests and simplify logic

src/patcher/paragraph-split-inject.ts

@@ -12,7 +12,7 @@ export const findRunElementIndexWithToken = (paragraphElement: Element, token: s
                     continue;
                 }
 
-                if ((text.elements?.[0].text as string)?.includes(token)) {
+                if ((text.elements[0].text as string)?.includes(token)) {
                     return i;
                 }
             }