Follow these simple steps...

Step 1: Go to settings.
Step 2: Click on Build Version: ####. It is Build Version: 194 in this screenshot.
Step 3: Check the box dac_developer_mode.
Step 4: Start a bot match.
How to Use.
Once you are in a bot match, click Open Debug Menu.

From here you can:

Spawn any item.
Summon any unit on any tier.
Spawn any creep.
Give +10 Gold.
Skip ahead to future rounds.

This lets you mess around with a lot of different things.