To develop it locally, you need to setup your maven environment.
That's the easy part, you just need to download the Maven binaries and extract it somewhere, then put the maven/bin folder on your PATH.
https://maven.apache.org/install.html
Don't forget to configure your JAVA_HOME environment variable.
To usefully contribute you'll have to setup a local database with installed latest utPLSQL v3 and utPLSQL-demo-project.
The demo-project will serve as your test user. See .travis.yml to see an example on how it can be installed.
By default tests are executed against app/app user of localhost:1521/XE database.
If you want to run tests against another database you may set DB_URL, DB_USER, DB_PASS environment variables.
When you have local database set up you can run the complete build including integration tests by executing
./gradlew buildTo build the project without local database you may disable integration tests.
./gradlew build -x intTestIf you want to skip the local database part, just run ./gradlew test.
You will be able to run ./gradle test because integration tests are executed in the separate intTest task as part of overall check.