You don't need to build a new cue tool to test it. Instead you can run the tests from the root.
To use the new tool you would still need to build and install it.
You can import these changes proposed by someone else into your local Git repository. On the Gerrit review page, click the "Download ▼" link in the upper right corner, copy the "Checkout" command and run it from your local Git repo. It will look something like this: