Ensure your server time is correct
One of the main causes for Robot Ninja failing to determine if a test order is created is that your web server clock/time is too far behind (or ahead). This can result in the WooCommerce REST API returning incorrect orders when querying by date/time.
To overcome this if you manage your own hosting please ensure your server time is correct by checking that NTP (or equivalent) is configured correctly. Alternatively if you use shared hosting you may need to contact your host for assistance.