diff --git a/Dockerfile b/Dockerfile
index 9d13a08..d47cd83 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -12,13 +12,17 @@ WORKDIR /var/www
 COPY . .
 
 # install dependencies
+RUN rm -rf vendor
 RUN composer install
 
 # to support loading the directory as volume, we'll move vendor out of the way so it
 # doesn't get overwritten by more recent code; we'll put it back before running anything
-RUN mv vendor ../vendor
-RUN echo 'cp -r /var/vendor /var/www/vendor && exec "$@"' > /etc/run.sh
-RUN chmod +x /etc/run.sh
+RUN mv vendor ../docker-vendor
+RUN echo 'mv /var/www/vendor /var/current-vendor 2>/dev/null || : && \
+    mv /var/docker-vendor /var/www/vendor && \
+    /bin/sh -c "$@" || : && \
+    mv /var/www/vendor /var/docker-vendor && \
+    mv /var/current-vendor /var/www/vendor 2>/dev/null || :' > /etc/run.sh
 ENTRYPOINT ["/bin/sh", "/etc/run.sh"]
 
 CMD ["vendor/bin/phpunit"]
diff --git a/makefile b/makefile
index 1c40be7..a37c9ef 100644
--- a/makefile
+++ b/makefile
@@ -3,3 +3,10 @@ docs:
 	chmod +x apigen.phar
 	php apigen.phar generate --source=src --destination=docs --template-theme=bootstrap
 	rm apigen.phar
+
+image:
+	docker build -t matthiasmullie/minify .
+
+test:
+	[ ! -z `docker images -q matthiasmullie/minify` ] || make image
+	docker run --rm --name minify -v `pwd`:/var/www matthiasmullie/minify vendor/bin/phpunit