Fix bug 1681 to run stage-test only if changes in installer charms

Change-Id: I36e66bd52b535f4f6aa97f877b6d17d9d34cd63a
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/devops-stages/stage-test.sh b/devops-stages/stage-test.sh
index 51b3513..70b610b 100755
--- a/devops-stages/stage-test.sh
+++ b/devops-stages/stage-test.sh
@@ -1,5 +1,6 @@
 #!/bin/sh
 #   Copyright 2021 Canonical Ltd.
+#   Copyright ETSI
 #
 #   Licensed under the Apache License, Version 2.0 (the "License");
 #   you may not use this file except in compliance with the License.
@@ -14,6 +15,11 @@
 #   limitations under the License.
 
 set -eu
+
+if [ $(git diff --name-only origin/$GERRIT_BRANCH -- installers/charm/ |wc -l) -eq 0 ]; then
+    exit 0
+fi
+
 CURRENT_DIR=`pwd`
 
 # Execute tests for charms
@@ -24,4 +30,4 @@
     OUTPUT=$(TOX_PARALLEL_NO_SPINNER=1 tox --parallel=auto)
     printf "$OUTPUT\n"
     cd $CURRENT_DIR
-done
\ No newline at end of file
+done