This site is using the standard WordPress Theme Unit Test Data for content. The Theme Unit Test is a series of posts and pages that match up with a checklist on the WordPress codex. You can use the data and checklist together to test your theme.

WordPress Theme Development Resources

1. See the WordPress Theme Developer Handbook for examples of best practices.
2. See the WordPress Code Reference for more information about WordPress’ functions, classes, methods, and hooks.
3. See Theme Unit Test for a robust test suite for your Theme and get the latest version of the test data you see here.
4. See Releasing Your Theme for a guide to submitting your Theme to the Theme Directory.