Pico Pico simplifies large scale Harware-In-the-Loop (HIL) testing of Pico embedded software. Each Pico Pico consists of two Picos, wired up such that one acts as a Pico Debug Probe, and the other acts as a Device Under Test (DUT).
Pico Pico is part of the Pigweed project. Nevertheless, Pico Pico is suitable for non-Pigweed projects since there is nothing Pigweed specific about the hardware.
The Pico Debug Probe requires modified debug probe firmware, since the pinout differs from the official probe.
Hardware In the Loop automated testing of software requires flashing new software, running tests against that software, then checking if the tests passed or failed. Unlike with unit tests on your desktop computer, when an embedded device crashes as part of a test it may not be in a state where you can update the software (e.g. it becomes bricked). By attaching a 2nd Pico as a Pico Debug Probe, un-sticking a crashed Pico to re-flash is possible.
Using the Pico Pico by re-flashing the same physical addresses regularly can burn out the flash. This could happen if hundreds of tests are run for each full test suite run, and full test suites are run nearly continuously. There isn't an easy solution for this. One solution is to link the firmware for RAM, load the image via the debug probe, and run the code there (eliminating the flash cycle). However, that limits the image size to the SRAM on the Pico, which is too small for many applications.
However, since the Pico boards are cheap they can be replaced easily.