Evite que le test plante si http_proxy n'est pas défini.

test/Dockerfile

@@ -4,7 +4,7 @@ FROM debian:${DEBIAN_VERSION}
 RUN sed -i -e '/^Templates:/aFrontend: noninteractive' /etc/debconf.conf
 
 ARG http_proxy
-RUN [ -n "$http_proxy" ] && echo 'Acquire::http::Proxy "'$http_proxy'";' >/etc/apt/apt.conf.d/80proxies
+RUN if [ -n "$http_proxy" ] ; then echo 'Acquire::http::Proxy "'$http_proxy'";' >/etc/apt/apt.conf.d/80proxies ; fi
 RUN echo 'Acquire::https::Proxy "DIRECT";' >>/etc/apt/apt.conf.d/80proxies
 
 RUN apt-get update -yqq