diff --git a/tests/run-tests b/tests/run-tests
--- a/tests/run-tests
+++ b/tests/run-tests
@@ -104,6 +104,27 @@ run_one() {
     return $fail
 }
 
+# list of prerequisite programs 
+# stuff from coreutils (cat, rm, etc) are not tested
+prereqs="python merge diff grep unzip md5sum gunzip sed"
+missing=''
+for pre in $prereqs ; do
+    if type $pre > /dev/null 2>&1 ; then
+        : prereq exists
+    else 
+        missing="$pre $missing"
+    fi
+done
+
+if [ "$missing" != ''  ] ; then
+    echo "ERROR: the test suite needs some programs to execute correctly."
+    echo "The following programs are missing: "
+    for pre in $missing; do
+        echo "   $pre"
+    done
+    exit 1
+fi
+
 TESTS="$*"
 if [ -z "$TESTS" ] ; then
     TESTS=`ls test-* | grep -v "[.~]"`