Added test fo password decryption command

src/test_libexim-encrypt-dlfunc-decrypt-secretbox.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+# shellcheck disable=SC2034
+
+set -e
+
+PATH=/sbin:/usr/sbin:$PATH
+
+TEST_PASSWORD='ThisIsAPassword'
+TEST_CLEARTEXT='This is my cleartext'
+TEST_CIPHERTEXT01='RCHI+VukmWIsVE3eixbWIAtPPBW63nmV1ITpSBEDYXC9Y5QMBd1zmGLLhE+S9yg0sHfOF/1+wmfF7YXv'
+TEST_CIPHERTEXT02='sEG09WnEKIN2nyJYGNNVo14o7wV6X9HQxW+zxAxMLX9jVdashdaoHqLXQGM8lzpJhG6629lccjzAfrq8'
+
+LIBEXIM_PASSWORD="${TEST_PASSWORD}"
+DECRYPTED01="$(src/libexim-encrypt-dlfunc-decrypt-secretbox ${TEST_CIPHERTEXT01})"
+
+if [ "${DECRYPTED01}" == "${TEST_CLEARTEXT}" ] ; then
+  echo "decryption with password from environment successful"
+else
+  echo "decryption with password from environment unsuccessful"
+  exit 127
+fi
+
+unset LIBEXIM_PASSWORD
+DECRYPTED02="$(src/libexim-encrypt-dlfunc-decrypt-secretbox -p ${TEST_PASSWORD} ${TEST_CIPHERTEXT02})"
+
+if [ "${DECRYPTED02}" == "${TEST_CLEARTEXT}" ] ; then
+  echo "decryption with password from commandline successful"
+else
+  echo "decryption with password from commandline unsuccessful"
+  exit 128
+fi