Add basic tests.

test/test.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+rm -f *.out
+
+# Run the tests.
+vim -N -u NONE -S test.vim
+
+# Verify the outputs.
+for expected in *.ok; do
+  name=${expected%.*}
+  actual=$name.out
+  diff $expected $actual && echo "$name ok" || echo "$name failed"
+done