tests: add version_to_tag roundtrip tests

tests/test_version_to_tag.sh

+#!/bin/sh
+
+. `dirname $0`/../share/eterbuild/functions/common
+load_mod git
+
+check()
+{
+	[ "$2" != "$3" ] && echo "FATAL with '$1': result '$2' do not match with '$3'" || echo "OK for '$1' with '$2'"
+}
+
+# version_to_tag
+check "tilde" "$(version_to_tag "1.0~rc1-alt1")" "1.0.tilde.rc1-alt1"
+check "plus" "$(version_to_tag "1.0+dfsg-alt1")" "1.0.plus.dfsg-alt1"
+check "both" "$(version_to_tag "1.0~rc1+dfsg-alt1")" "1.0.tilde.rc1.plus.dfsg-alt1"
+check "no special" "$(version_to_tag "1.0-alt1")" "1.0-alt1"
+check "multiple tilde" "$(version_to_tag "1.0~alpha~1-alt1")" "1.0.tilde.alpha.tilde.1-alt1"
+
+# tag_to_version
+check "tilde back" "$(tag_to_version "1.0.tilde.rc1-alt1")" "1.0~rc1-alt1"
+check "plus back" "$(tag_to_version "1.0.plus.dfsg-alt1")" "1.0+dfsg-alt1"
+check "both back" "$(tag_to_version "1.0.tilde.rc1.plus.dfsg-alt1")" "1.0~rc1+dfsg-alt1"
+check "no special back" "$(tag_to_version "1.0-alt1")" "1.0-alt1"
+
+# roundtrip
+for ver in "1.0~rc1-alt1" "2.3+dfsg-alt2" "1.0~beta1+repack-alt1" "3.14-alt1" ; do
+	check "roundtrip $ver" "$(tag_to_version "$(version_to_tag "$ver")")" "$ver"
+done