Tests - use Docker (as environment guard)

.docker/config/Dockerfile

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+FROM php:5.6-cli
+
+#
+# Tools & libraries
+#
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends \
+        vim \
+        git \
+        zip \
+        unzip \
+        zlib1g-dev \
+        libicu-dev \
+    && apt-get clean \
+    && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+
+#
+# PHP extensions
+#
+RUN docker-php-ext-install \
+    zip \
+    intl \
+    mbstring
+
+#
+# PHP configuration:
+# - default configuration
+# - timezone
+#
+COPY php.ini /usr/local/etc/php/php.ini
+ARG TIMEZONE
+RUN echo "\n""date.timezone = $TIMEZONE""\n" >> /usr/local/etc/php/php.ini
+
+#
+# Xdebug
+#
+RUN pecl install xdebug \
+    && docker-php-ext-enable xdebug
+COPY xdebug.ini /usr/local/etc/php/conf.d/docker-php-ext-xdebug.ini
+
+#
+# Phing
+#
+RUN pear channel-discover pear.phing.info \
+    && pear install [--alldeps] phing/phing
+
+#
+# Composer + https://packagist.org/packages/hirak/prestissimo package
+#
+RUN php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');" \
+    && php -r "if (hash_file('SHA384', 'composer-setup.php') === \
+    '544e09ee996cdf60ece3804abc52599c22b1f40f4323403c44d44fdfdd586475ca9813a858088ffbc1f233e9b180f061') { echo \
+    'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); } echo PHP_EOL;" \
+    && php composer-setup.php --install-dir=/usr/local/bin --filename=composer \
+    && php -r "unlink('composer-setup.php');" \
+    && composer global require --no-plugins --no-scripts hirak/prestissimo \
+    && rm -rf /root/.composer/cache/*
+
+#
+# Bash
+#
+RUN sed -i 's/^# export/export/g' /root/.bashrc \
+    && sed -i 's/^# alias/alias/g' /root/.bashrc \
+    && echo "\n"'export PATH=/project/vendor/bin:$PATH'"\n" >> /root/.bashrc

.docker/config/php.ini

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+display_errors = On
+display_startup_errors = On
+error_reporting = E_ALL

.docker/config/xdebug.ini

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+[xdebug]
+zend_extension='xdebug.so'
+
+xdebug.remote_enable=1
+xdebug.remote_connect_back=1
+xdebug.idekey='PHPSTORM'
+xdebug.remote_port=9001