tests: add test for XDG and SNAP variables

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@canonical.com>

tests/main/snap-env/task.yaml

@@ -0,0 +1,31 @@
+summary: inspect all the set environment variables prefixed with SNAP_ and XDG_
+prepare: |
+    snapbuild $TESTSLIB/snaps/test-snapd-tools .
+    snap install --dangerous test-snapd-tools_1.0_all.snap
+restore: |
+    rm -f *.snap
+execute: |
+    echo "Collect SNAP and XDG environment variables"
+    test-snapd-tools.env | egrep '^SNAP_' | sort > snap-vars.txt 
+    test-snapd-tools.env | egrep '^XDG_' | sort > xdg-vars.txt 
+
+    echo "Ensure that SNAP environment variables are what we expect"
+    egrep -q '^SNAP_ARCH=(amd64|i386|arm64|armhf)$' snap-vars.txt
+    egrep -q '^SNAP_COMMON=/var/snap/test-snapd-tools/common$' snap-vars.txt
+    egrep -q '^SNAP_DATA=/var/snap/test-snapd-tools/x1$' snap-vars.txt
+    egrep -q '^SNAP_LIBRARY_PATH=/var/lib/snapd/lib/gl:$' snap-vars.txt
+    egrep -q '^SNAP_NAME=test-snapd-tools$' snap-vars.txt
+    # XXX: probably not something we ough to test
+    # egrep -q '^SNAP_REEXEC=0$' snap-vars.txt
+    egrep -q '^SNAP_REVISION=x1$' snap-vars.txt
+    egrep -q '^SNAP_USER_COMMON=/root/snap/test-snapd-tools/common$' snap-vars.txt
+    egrep -q '^SNAP_USER_DATA=/root/snap/test-snapd-tools/x1$' snap-vars.txt
+    egrep -q '^SNAP_VERSION=1.0$' snap-vars.txt
+    test $(wc -l < snap-vars.txt) -eq 10
+
+    echo "Enure that XDG environment variables are what we expect"
+    egrep -q '^XDG_RUNTIME_DIR=/run/user/0/snap.test-snapd-tools$' xdg-vars.txt
+    egrep -q '^XDG_SESSION_ID=1$' xdg-vars.txt
+    test $(wc -l < xdg-vars.txt) -eq 2
+debug: |
+    cat *-vars.txt