What theme unit tests are, why you would use them, and some of the different options available.

1. Theme Unit Tests
WordPress sample content

2. What are Theme Unit Tests?
Two forms:
1. XML file (import via Tools > Import > WordPress
2. Plugin
Provide sample content to test theme styles

3. Why use them?
Test theme candidates for your site or a project
Save time later by testing styles now
Check your own theme development
Make sure your own themes support all default
WordPress content features
Don’t release incomplete themes

4. WordPress.org
codex.wordpress.org/
Theme_Unit_Test
wpthemetestdata.wordpress.com/
Images, embeds
Visual Editor styles
Post formats
Categories & tags
Titles, excerpts, more tag,
password, pagination etc

5. WP Test
wptest.io
Based on wp.org's
Theme Unit Test
Cool images
Fewer nonsense
categories
Straight forward post titles

6. Plugin: Demo Data Creator
wordpress.org/plugins/demo-data-creator/
Has options page
Supports:
User creation
BuddyPress
Multisite

7. Plugin: WP Lipsum
wordpress.org/plugins/
wp-lipsum/
Uses shortcodes or
template tag
May be easier to use
on development site

8. Plugin: WP Example
Content
http://wordpress.org/plugins/wp-example-content
Set bundle of 6 posts
Formatting, images, lists, links, blockquotes
One-button sample posts removal