createmobilespec.js is a script for creating a test app that has:
the mobile-spec code from the local cordova-mobile-spec git repo
a cordova.js file that is freshly built from the local cordova-js git repo
the platform (e.g., Android) from the local platform git repo (e.g., cordova-android)
all the plugins from the local plugin repos (e.g., cordova-plugin-device)
it was built using the local cordova-cli and cordova-plugman git repos
Many places in this document that say git repo may also mean npm repository.
In other words, it is a great way to test your local development efforts.
The script also has options for creating the test app using a globally-installed npm module, a way to use the platform's cordova.js file instead of building it from the local cordova-js git repo, and a way to use the platform-centered workflow instead of the CLI.
See the README.md in the parent directory cordova-mobile-spec.
Each git repo should be checked out to the state or edited with the content that you want to test. Be aware that it will download missing plugin content from the plugin registry nor does it fetch platforms from the npm repository.
Except, I think it does...
Before running createmobilespec.js for the first time, run npm install from within the createmobilespec directory to install the requisite third-party Node modules. This should be a one-time activity, unless there is a change in the pre-reqs.
The createmobilespec.js script needs to be invoked from a specific current working directory: the one where you have all the git repos cloned. So if you were to do an ls in that directory, you should see all the git repos including cordova-mobile-spec. Thus an invocation should look like:
cordova-mobile-spec/createmobilespec/createmobilespec.js
To see the options available in the script, run it with the -h option to print the online help.
After you have run the script to create the app, then you can run the app on a device or simulator, using the standard method for that platform(s). For example on Android:
cd mobilespec
./cordova run android