Use bash, so echo -n will do the right thing.
diff --git a/runtests.sh b/runtests.sh
index d5b1c35..93ef833 100755
--- a/runtests.sh
+++ b/runtests.sh
@@ -1,4 +1,4 @@
-#!/bin/sh
+#!/bin/bash
 
 HELP="Usage: ./runtests.py [-h] [-x] [flags] [tests]