In order to be included in the Learn Mode quiz, the words and captions tested must satisfy the following conditions:
1) Words are only tested if they are featured vocab (ie. underlined).
2) Captions are only tested if they include at least one featured vocab.
If you'd like to get tested on words that aren't featured, you must manually add them to your My Vocab section. After you review them once there, they will be added to your Ready for Review section.