Sign it live. Then verify it yourself.
This signs a real transaction on Bitcoin's public test network. The authority to move funds is split, so no single key can act alone. When it finishes, do not take this screen's word for it. Look the transaction up yourself, on your own phone, on a public explorer this page does not control.
Research prototype. Each run sends the wallet's test coins back to itself, so it stays funded, and creates a new transaction you can check independently.
Now confirm it independently.
The transaction below is live on the public network. Check it two ways, neither on software this page controls: scan it with your own phone, and watch it read back live from a public explorer.