diff --git a/tests/renderdot.py b/tests/renderdot.py
new file mode 100644
index 0000000..597e68b
--- /dev/null
+++ b/tests/renderdot.py
@@ -0,0 +1,73 @@
+import sys
+
+class Renderer(object):
+
+    def __init__(self, getleft, getright,
+                 getred, getstart, getend, nil):
+        self.getleft = getleft
+        self.getright = getright
+        self.getred = getred
+        self.getstart = getstart
+        self.getend = getend
+        self.nil = nil
+
+    # Rendering
+    def __render_dot_node(self, node, max_depth = 20):
+        from nilmdb.printf import sprintf
+        """Render a single node and its children into a dot graph fragment"""
+        if max_depth == 0:
+            return ""
+        if node is self.nil:
+            return ""
+        def c(red):
+            if red:
+                return 'color="#ff0000", style=filled, fillcolor="#ffc0c0"'
+            else:
+                return 'color="#000000", style=filled, fillcolor="#c0c0c0"'
+        s = sprintf("%d [label=\"%g\\n%g\", %s];\n",
+                    id(node),
+                    self.getstart(node), self.getend(node),
+                    c(self.getred(node)))
+
+        if self.getleft(node) is self.nil:
+            s += sprintf("L%d [label=\"-\", %s];\n", id(node), c(False))
+            s += sprintf("%d -> L%d [label=L];\n", id(node), id(node))
+        else:
+            s += sprintf("%d -> %d [label=L];\n",
+                         id(node),id(self.getleft(node)))
+        if self.getright(node) is self.nil:
+            s += sprintf("R%d [label=\"-\", %s];\n", id(node), c(False))
+            s += sprintf("%d -> R%d [label=R];\n", id(node), id(node))
+        else:
+            s += sprintf("%d -> %d [label=R];\n",
+                         id(node), id(self.getright(node)))
+        s += self.__render_dot_node(self.getleft(node), max_depth-1)
+        s += self.__render_dot_node(self.getright(node), max_depth-1)
+        return s
+
+    def render_dot(self, rootnode, title = "Tree"):
+        """Render the entire tree as a dot graph"""
+        return ("digraph rbtree {\n"
+                + self.__render_dot_node(rootnode)
+                + "}\n");
+
+    def render_dot_live(self, rootnode, title = "Tree"):
+        """Render the entiretree as a dot graph, live GTK view"""
+        import gtk
+        import gtk.gdk
+        sys.path.append("/usr/share/xdot")
+        import xdot
+        xdot.Pen.highlighted = lambda pen: pen
+        s = ("digraph rbtree {\n"
+             + self.__render_dot_node(rootnode)
+             + "}\n");
+        window = xdot.DotWindow()
+        window.set_dotcode(s)
+        window.set_title(title + " - any key to close")
+        window.connect('destroy', gtk.main_quit)
+        def quit(widget, event):
+            if not event.is_modifier:
+                window.destroy()
+                gtk.main_quit()
+        window.widget.connect('key-press-event', quit)
+        gtk.main()
diff --git a/tests/test_interval.py b/tests/test_interval.py
index 839922d..7e06746 100644
--- a/tests/test_interval.py
+++ b/tests/test_interval.py
@@ -270,6 +270,7 @@ class TestIntervalDB:
 class TestIntervalTree:
 
     def test_interval_tree(self):
+        import renderdot
         import random
         random.seed(1234)
 
@@ -280,6 +281,15 @@ class TestIntervalTree:
             interval = Interval(i, i+1)
             iset += interval
 
+        # Plot it
+        r = renderdot.Renderer(lambda node: node.cleft,
+                               lambda node: node.cright,
+                               lambda node: False,
+                               lambda node: node.start,
+                               lambda node: node.end,
+                               iset.tree.emptynode())
+        r.render_dot_live(iset.tree.rootnode(), "Random insertion")
+
         # remove about half of them
         for i in random.sample(xrange(j),j):
             if random.randint(0,1):
@@ -289,9 +299,32 @@ class TestIntervalTree:
         with assert_raises(IntervalError):
             iset -= Interval(1234,5678)
 
-        # show the graph
-        if False:
-            iset.tree.render_dot_live()
+        # Plot it
+        r = renderdot.Renderer(lambda node: node.cleft,
+                               lambda node: node.cright,
+                               lambda node: False,
+                               lambda node: node.start,
+                               lambda node: node.end,
+                               iset.tree.emptynode())
+        r.render_dot_live(iset.tree.rootnode(), "Random insertion, deletion")
+
+        # make a set of 500 intervals, inserted in order
+        iset = IntervalSet()
+        j = 500
+        for i in xrange(j):
+            interval = Interval(i, i+1)
+            iset += interval
+
+        # Plot it
+        r = renderdot.Renderer(lambda node: node.cleft,
+                               lambda node: node.cright,
+                               lambda node: False,
+                               lambda node: node.start,
+                               lambda node: node.end,
+                               iset.tree.emptynode())
+        r.render_dot_live(iset.tree.rootnode(), "In-order insertion")
+
+        assert(False)
 
 class TestIntervalSpeed:
     @unittest.skip("this is slow")