diff --git a/functions b/functions
index a80d06d471..a3e95370fb 100644
--- a/functions
+++ b/functions
@@ -142,6 +142,8 @@ GetOSVersion() {
 # be owned by the installation user, we create the directory and change the
 # ownership to the proper user.
 # Set global RECLONE=yes to simulate a clone when dest-dir exists
+# Set global ERROR_ON_CLONE=True to abort execution with an error if the git repo
+# does not exist (default is False, meaning the repo will be cloned).
 # git_clone remote dest-dir branch
 function git_clone {
     [[ "$OFFLINE" = "True" ]] && return
@@ -153,6 +155,7 @@ function git_clone {
     if echo $GIT_BRANCH | egrep -q "^refs"; then
         # If our branch name is a gerrit style refs/changes/...
         if [[ ! -d $GIT_DEST ]]; then
+            [[ "$ERROR_ON_CLONE" = "True" ]] && exit 1
             git clone $GIT_REMOTE $GIT_DEST
         fi
         cd $GIT_DEST
@@ -160,6 +163,7 @@ function git_clone {
     else
         # do a full clone only if the directory doesn't exist
         if [[ ! -d $GIT_DEST ]]; then
+            [[ "$ERROR_ON_CLONE" = "True" ]] && exit 1
             git clone $GIT_REMOTE $GIT_DEST
             cd $GIT_DEST
             # This checkout syntax works for both branches and tags
diff --git a/stack.sh b/stack.sh
index 3bb19bccbf..f11b5e24d1 100755
--- a/stack.sh
+++ b/stack.sh
@@ -214,6 +214,11 @@ fi
 # prerequisites and initialize ``$DEST``.
 OFFLINE=`trueorfalse False $OFFLINE`
 
+# Set True to configure ``stack.sh`` to exit with an error code if it is asked
+# to clone any git repositories.  If devstack is used in a testing environment,
+# this may be used to ensure that the correct code is being tested.
+ERROR_ON_CLONE=`trueorfalse False $ERROR_ON_CLONE`
+
 # Destination path for service data
 DATA_DIR=${DATA_DIR:-${DEST}/data}
 sudo mkdir -p $DATA_DIR