Setting up Cassandra database service on TravisCI

At this time of writing TravisCI says that if you want to run a Cassandra service you have to add a cassandra service according to https://docs.travis-ci.com/user/database-setup/#cassandra:

services:
  - cassandra

but if you try to initialize cassandra you might find out that cassandra is not yet ready or running depending on timing.

The solution is:

• a .travis.yml file (see https://github.com/davidemoro/pytest-play-docker/blob/master/.travis.yml) with the cassandra service and a "bash travis/setup_cassandra.sh" command in before_script section
• a travis/setup_cassandra.sh (see https://github.com/davidemoro/pytest-play-docker/blob/master/travis/setup_cassandra.sh) that waits for cassandra up and running (e.g., a sleep 30, a polling loop with max retries implemented in my travis/setup_cassandra.sh script or using docker service) before cqlsh initialization commands

And now cassandra is ready to be used in your tests (for example https://github.com/davidemoro/pytest-play-docker/blob/master/tests/test_cassandra.yml . In this case I'm using using plain yml files thanks to pytest-play)

	sudo: required
	services:
	- cassandra
	before_script:
	- bash travis/setup_cassandra.sh
	script:
	- ... run test

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	#!/bin/bash
	function cassandra_ready() {
	count=0
	while ! cqlsh -e "describe cluster;" 2>&1 ; do
	echo "waiting for cassandra"
	if [ $count -gt 30 ]
	then
	exit
	fi
	(( count += 1 ))
	sleep 1
	done
	echo "cassandra is ready"
	}
	cassandra_ready
	cqlsh -e "create keyspace dev with replication = {'class': 'SimpleStrategy', 'replication_factor': 1}; USE dev; create table play(code int primary key, title varchar); insert into play (code, title) values (1, 'hello!');"

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	---
	- provider: play_cassandra
	type: execute
	connection:
	contact_points:
	- 127.0.0.1
	port: 9042
	auth_provider:
	username: cassandra
	password: cassandra
	keyspace: dev
	query: SELECT title from play WHERE code = 1;
	variable: title
	variable_expression: results[0].title
	assertion: "'$title' == 'hello!'"

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