Add script to update external test repo commit pointers

It will prompt to update the file storing the external test repo
commit hash when a change is detected upon running update-changes.

testing/scripts/update-external-repo-pointer.sh

@@ -0,0 +1,49 @@
+#! /usr/bin/env bash
+
+set -e
+
+if [ $# -ne 2 ]; then
+    echo "usage: $0 <external repo path> <file to store commit in>"
+    exit 1
+fi
+
+repo_dir=$1
+hash_file=$2
+
+repo_base=$(basename $repo_dir)
+file_base=$(basename $hash_file)
+
+if [ ! -d "$repo_dir" ]; then
+    echo "External repo does not exist: $repo_dir"
+    exit 1
+fi
+
+printf "Checking for '$repo_base' changes ..."
+
+origin_hash=$(cd $repo_dir && git fetch origin && git rev-parse origin/master)
+head_hash=$(cd $repo_dir && git rev-parse HEAD)
+file_hash=$(cat $hash_file)
+
+if [ "$file_hash" != "$head_hash" ]; then
+    printf "\n"
+    printf "\n"
+    printf "  '$repo_base' pointer has changed:\n"
+
+    line="    $file_base at $file_hash"
+    len=${#line}
+
+    printf "%${len}s\n" "$line"
+    printf "%${len}s\n" "origin/master at $origin_hash"
+    printf "%${len}s\n" "HEAD at $head_hash"
+    printf "\n"
+    printf "Update file '$file_base' to HEAD commit ? "
+
+    read -p "[Y/n] " choice
+
+    case "$choice" in
+        n|N) echo "Skipped '$repo_base'";;
+        *) echo $head_hash > $hash_file  && git add $hash_file && echo "Updated '$file_base'";;
+    esac
+else
+    echo " none"
+fi