Install the Wordpress PHPUnit test framework from the same branch as the WordPress version you test against. The benefit over WP-CLI unit tests scaffolding is that you can test any version without fatal errors for undifined functions or classes

bootstrap.php

<?php

$_tests_dir = '/tmp/wordpress-tests-lib';

require_once $_tests_dir . '/includes/functions.php';

function _manually_load_plugin() {
	require dirname( dirname( __FILE__ ) ) . '/ddd.php';
}
tests_add_filter( 'muplugins_loaded', '_manually_load_plugin' );

require $_tests_dir . '/includes/bootstrap.php';

install-wp-tests.sh

#!/usr/bin/env bash

if [ $# -lt 3 ]; then
	echo "usage: $0 <db-name> <db-user> <db-pass> [db-host] [wp-version]"
	exit 1
fi

DB_NAME=$1
DB_USER=$2
DB_PASS=$3
DB_HOST=${4-localhost}
WP_VERSION=${5-latest}
TEST_SUITE_VERSION=${6-wp_version}

# To test release candidates use
# bash bin/install-wp-tests.sh wordpress_test root '' localhost 4.5-RC1 trunk

WP_TESTS_DIR=/tmp/wordpress-tests-lib
WP_CORE_DIR=/tmp/wordpress/

#remove trailing slash
WP_CORE_DIR=${WP_CORE_DIR%/}

set -ex

download() {
	if [ `which curl` ]; then
		curl -s "$1" > "$2";
	elif [ `which wget` ]; then
		wget -nv -O "$2" "$1"
	fi
}

wp_core_version(){
	local version='trunk'

	if [ -f $WP_CORE_DIR/wp-includes/version.php ]; then
		if grep -q "wp_version = " $WP_CORE_DIR/wp-includes/version.php; then
			version=$(grep "wp_version = " $WP_CORE_DIR/wp-includes/version.php|awk -F\' '{print $2}')
		fi
	fi

	echo $version
}

wp_api_version(){
	local latest=''
	local api_url="http://api.wordpress.org/core/version-check/1.5/"

	if [ `which curl` ]; then
		latest=$(curl -s "$api_url" | head -n 4 | tail -n 1)
	elif [ `which wget` ]; then
		latest=$(wget -S -q -O - "$api_url" | head -n 4 | tail -n 1);
	fi

	echo $latest
}

wp_download_exists(){
	if [ `which curl` ]; then
		$(curl --output /dev/null --silent --head --fail "$1");
	elif [ `which wget` ]; then
		$(wget --spider $1 >/dev/null 2>&1);
	fi
}

install_wp() {

	if [ $WP_VERSION == 'latest' ]; then

		local archive_name='latest'
		local latest=$(wp_api_version)
		local url=https://wordpress.org/"wordpress-$latest".tar.gz

		# check if latest version exists
		if wp_download_exists $url; then
			WP_VERSION=$latest
			archive_name="wordpress-$latest"
		fi
	else
		local archive_name="wordpress-$WP_VERSION"
	fi

	local core_version=$(wp_core_version)

	if [ $core_version != 'trunk' ]; then
		if [ $core_version == $WP_VERSION ]; then
			return
		fi
	fi

	mkdir -p $WP_CORE_DIR

	if wp_download_exists "https://wordpress.org/${archive_name}.tar.gz"; then

		download https://wordpress.org/${archive_name}.tar.gz  /tmp/wordpress.tar.gz
		tar --strip-components=1 -zxmf /tmp/wordpress.tar.gz -C "$WP_CORE_DIR"

		download https://raw.github.com/markoheijnen/wp-mysqli/master/db.php "$WP_CORE_DIR/wp-content/db.php"
	else
		echo "Error: WordPress version not found."
		exit
	fi
}

install_test_suite() {
	# portable in-place argument for both GNU sed and Mac OSX sed
	if [[ $(uname -s) == 'Darwin' ]]; then
		local ioption='-i .bak'
	else
		local ioption='-i'
	fi

	# get the version from the installed WordPress version
	local core_version=$(wp_core_version)

	if [ $core_version != 'trunk' ]; then
		core_version="tags/"$core_version
	fi

	if [ $TEST_SUITE_VERSION != 'wp_version' ]; then
		if [ $TEST_SUITE_VERSION != 'trunk' ]; then
			core_version="tags/"$TEST_SUITE_VERSION
		else
			core_version='trunk'
		fi
	fi

	# Set up the testing suite from the core version
	mkdir -p $WP_TESTS_DIR

	if wp_download_exists "https://develop.svn.wordpress.org/$core_version/wp-tests-config-sample.php"; then

		svn export --quiet --force https://develop.svn.wordpress.org/$core_version/tests/phpunit/includes/ $WP_TESTS_DIR/includes
		cd $WP_TESTS_DIR

		download https://develop.svn.wordpress.org/$core_version/wp-tests-config-sample.php "$WP_TESTS_DIR"/wp-tests-config.php
		sed $ioption "s:dirname( __FILE__ ) . '/src/':'$WP_CORE_DIR/':" "$WP_TESTS_DIR"/wp-tests-config.php
		sed $ioption "s/youremptytestdbnamehere/$DB_NAME/" "$WP_TESTS_DIR"/wp-tests-config.php
		sed $ioption "s/yourusernamehere/$DB_USER/" "$WP_TESTS_DIR"/wp-tests-config.php
		sed $ioption "s/yourpasswordhere/$DB_PASS/" "$WP_TESTS_DIR"/wp-tests-config.php
		sed $ioption "s|localhost|${DB_HOST}|" "$WP_TESTS_DIR"/wp-tests-config.php
	fi
}

install_db() {
	# parse DB_HOST for port or socket references
	local PARTS=(${DB_HOST//\:/ })
	local DB_HOSTNAME=${PARTS[0]};
	local DB_SOCK_OR_PORT=${PARTS[1]};
	local EXTRA=""

	if ! [ -z $DB_HOSTNAME ] ; then
		if [ $(echo $DB_SOCK_OR_PORT | grep -e '^[0-9]\{1,\}$') ]; then
			EXTRA=" --host=$DB_HOSTNAME --port=$DB_SOCK_OR_PORT --protocol=tcp"
		elif ! [ -z $DB_SOCK_OR_PORT ] ; then
			EXTRA=" --socket=$DB_SOCK_OR_PORT"
		elif ! [ -z $DB_HOSTNAME ] ; then
			EXTRA=" --host=$DB_HOSTNAME --protocol=tcp"
		fi
	fi

	# create database
	mysqladmin create $DB_NAME --user="$DB_USER" --password="$DB_PASS"$EXTRA
}

install_wp
install_test_suite
install_db

For more information see: https://keesiemeijer.wordpress.com/2015/10/07/failing-unit-tests-because-of-undefined-functions/

To tests your plugin with release candidates you'll need to use the test suite from trunk. Release candidates don't have their own test suite. Use the test suite version parameter (last parameter) and set it to trunk.

 bash bin/install-wp-tests.sh wordpress_test root '' localhost 4.5-RC1 trunk