You’ll notice that the installation command specified --no-dev. This prevents Composer from installing the various testing and development dependencies. For average users, there is no need to install the test suite. In particular, the development dependencies include a full copy of Elasticsearch so that tests can be run against the REST specifications. This is a rather large download for non-developers, hence the --no-dev flag

If you wish to contribute to development of this library, just omit the --no-dev flag to be able to run tests.