Ensure $SHELL is set for the tests

Non-interactive shells might not set it (this is true for dash
and mksh, at least). Currently we use $SHELL in whatnow(1).
Although we likely remove this use, it's rather worthwhile to
have $SHELL available in the test scripts.

diff --git a/test/runtest b/test/runtest
index 498db05..9f35ade 100755 (executable)
--- a/test/runtest
+++ b/test/runtest
@@ -51,6 +51,7 @@ folder +inbox >/dev/null
 
 # now run the test
 set +e
+export SHELL="${SHELL:-/bin/sh}"
 /bin/sh "$1"
 return_value=$?
 set -e