Merge remote-tracking branch 'mroth/osx-testing' into osx-testing

run_tests.sh

@@ -3,8 +3,15 @@
 
 failed=false
 
+# allow list of shells to run tests in to be overriden by environment variable
+# if empty or null, use defaults
+if [ -z "$TEST_SHELLS" ]; then
+  TEST_SHELLS="bash zsh"
+fi
+
+echo "== Will run all tests with following shells: ${TEST_SHELLS}"
 for test in $(find test/lib -name *_test.sh); do
-  for shell in bash zsh; do
+  for shell in $TEST_SHELLS; do
     echo "== Running tests with [$shell]: $test"
     $shell $test || failed=true
   done