diff -r efd9c589177a -r c0b4a8b5a012 toolkit/javascript/d3/test/core/transition-test-styleTween.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/javascript/d3/test/core/transition-test-styleTween.js	Thu Apr 10 14:20:23 2014 +0200
@@ -0,0 +1,73 @@
+require("../env");
+require("../../d3");
+
+var assert = require("assert");
+
+module.exports = {
+  topic: function() {
+    var cb = this.callback,
+        dd = [],
+        ii = [],
+        tt = [],
+        vv = [],
+        fails = 0;
+
+    var s = d3.select("body").html("").append("div").selectAll("div")
+        .data(["red", "green"])
+      .enter().append("div")
+        .style("background-color", function(d) { return d3.rgb(d)+""; });
+
+    var t = s.transition()
+        .styleTween("background-color", function() { ++fails; })
+        .styleTween("background-color", tween);
+
+    function tween(d, i, v) {
+      dd.push(d);
+      ii.push(i);
+      vv.push(v);
+      if (tt.push(this) >= 2) cb(null, {
+        selection: s,
+        transition: t,
+        data: dd,
+        index: ii,
+        value: vv,
+        context: tt,
+        fails: fails
+      });
+      return i && d3.interpolateHsl(v, "blue");
+    }
+  },
+
+  // The order here is a bit brittle: because the transition has zero delay,
+  // it's invoking the start event immediately for all nodes, rather than
+  // pushing each node onto the timer queue (which would reverse the order of
+  // callbacks). The order in which tweens are invoked is undefined, so perhaps
+  // we should sort the expected and actual values before comparing.
+
+  "defines the corresponding style tween": function(result) {
+    assert.typeOf(result.transition.tween("style.background-color"), "function");
+  },
+  "the last style tween takes precedence": function(result) {
+    assert.equal(result.fails, 0);
+  },
+  "invokes the tween function": function(result) {
+    assert.deepEqual(result.data, ["red", "green"], "expected data, got {actual}");
+    assert.deepEqual(result.index, [0, 1], "expected data, got {actual}");
+    assert.deepEqual(result.value, ["#ff0000", "#008000"], "expected value, got {actual}");
+    assert.domEqual(result.context[0], result.selection[0][0], "expected this, got {actual}");
+    assert.domEqual(result.context[1], result.selection[0][1], "expected this, got {actual}");
+  },
+
+  "end": {
+    topic: function(result) {
+      var cb = this.callback;
+      result.transition.each("end", function(d, i) { if (i >= 1) cb(null, result); });
+    },
+    "uses the returned interpolator": function(result) {
+      assert.equal(result.selection[0][1].style.getPropertyValue("background-color"), "#0000ff");
+    },
+    "does nothing if the interpolator is falsey": function(result) {
+      assert.equal(result.selection[0][0].style.getPropertyValue("background-color"), "#ff0000");
+    }
+  }
+};