Our code also depends on a running instance of Elasticsearch; therefore, we need to specify this requirement in the .travis.yml file by adding a services property:

services:
  - elasticsearch

This will install and start Elasticsearch on the Travis server instance using the default configuration (namely, port 9200). However, it is advisable to run a specific version of Elasticsearch—the same version we are running locally—to ensure we get results that are consistent with our development environment. Therefore, below the services block, add the following before_install block:

before_install:
  - curl -O https://artifacts.elastic.co/downloads/elasticsearch/elasticsearch-6.3.2.deb
  - sudo dpkg -i --force-confnew elasticsearch-6.3.2.deb
  - sudo service elasticsearch restart

The Elasticsearch service may take some time to start; therefore, we should also tell Travis to wait a few seconds before attempting to run the tests.

before_script:
  - sleep 10