Skip undefined functions when processing TESTS

Do not attempt to invoke test functions specified via the TESTS
environment variable if they are not defined. The Makefile invokes
multiple test scripts and each test function is only defined in one of
them.

Author: cjolowicz

test/utils

@@ -269,7 +269,9 @@ assertFile() {
 if [ -n "$TESTS" ]; then
     suite() {
         for shunit_func_ in ${TESTS}; do
-            suite_addTest ${shunit_func_}
+            if declare -F ${shunit_func_} > /dev/null; then
+                suite_addTest ${shunit_func_}
+            fi
         done
         unset shunit_func_
     }