I figured out what was going on. I didn’t right-click the above theme-unit-test-data.xml link and select “save link as” (Windows). Instead I must have copied and pasted, which introduced a bunch of odd characters to the XML.
The fix:
1. I had to drop all the tables in the database,
2. re-install WordPress
3. re-install/activate the theme
4. import the proper theme unit test data
5. re-install plugins
6. make all the back-end changes that I made before dropping the tables.
