`assert` added to test runner

test/run-test

@@ -29,6 +29,22 @@ cd "$( dirname "$0" )/../" || {
 }
 
 
+##
+# Provide command to output assertion on failure
+#
+# We do not override the `test` builtin, as this would also affect pkgsh
+# itself.
+#
+assert()
+{
+  test "$@" || {
+    local -i code=$?
+    echo "assertion failed: $@" >&2
+    return $code
+  }
+}
+
+
 main()
 {
   local tpath="$1"