add script and Makefile target to test multiverse in a docker container

Makefile

@@ -1,3 +1,5 @@
+DIST	:= "ubuntu:latest"
+
 cosmos:
 	fab all cosmos
 
@@ -10,3 +12,9 @@ db:
 
 tag: db
 	./bump-tag
+
+test_in_docker:
+	docker run --rm -it \
+		-v ${CURDIR}:/multiverse:ro \
+		\
+		$(DIST) /multiverse/scripts/test-in-docker.sh

scripts/test-in-docker.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+#
+# This script runs in a Docker container (started with the 'make test_in_docker' command)
+# and installs multiverse as it is in your source directory.
+#
+
+set -e
+
+apt -y update
+apt -y install git rsync gpg
+
+cosmos_deb=$(find /multiverse/apt/ -maxdepth 1 -name 'cosmos_*.deb' | sort -V | tail -1)
+dpkg -i "$cosmos_deb"
+
+test -d /var/cache/cosmos/repo || mkdir -p /var/cache/cosmos/repo
+test -d /var/cache/cosmos/model || mkdir -p /var/cache/cosmos/model
+
+# Make every "cosmos update" copy the contents from /multiverse
+# without requiring the changes in there to be checked into git.
+cat >/etc/cosmos/update.d/50update-while-testing << EOF
+#!/bin/sh
+
+rsync -a --delete --exclude .git /multiverse/ /var/cache/cosmos/repo
+EOF
+chmod 755 /etc/cosmos/update.d/50update-while-testing
+
+sed -i -e 's!^#COSMOS_REPO_MODELS=.*!COSMOS_REPO_MODELS="\$COSMOS_REPO/global/"!' /etc/cosmos/cosmos.conf
+
+export DEBIAN_FRONTEND=noninteractive
+
+echo ""
+echo "***"
+echo ""
+echo "$0: Configured docker container for testing of files in /multiverse."
+echo ""
+echo "You should now be able to do"
+echo ""
+echo "  cosmos -v update"
+echo "  cosmos -v apply"
+echo ""
+
+exec bash -l