text: var assert = require("../assert");
  
  module.exports = {
    topic: function(d3) {
      var s = d3.select("body").append("div")
          .style("background-color", "white")
          .style("color", "red")
          .style("display", "none")
          .style("font-size", "20px");
  
      var t = s.transition()
          .style("display", null)
          .style("font-size", function() { return null; })
          .style("display", null)
          .style("background-color", "green")
          .style("background-color", "red")
          .style("color", function() { return "green"; }, "important");
  
      return {selection: s, transition: t};
    },
    "defines the corresponding style tween": function(result) {
      assert.typeOf(result.transition.tween("style.background-color"), "function");
      assert.typeOf(result.transition.tween("style.color"), "function");
    },
    "on end": {
      topic: function(result) {
        var cb = this.callback;
        result.transition.each("end", function() { cb(null, result); });
      },
      "the last style operator takes precedence": function(result) {
        assert.equal(result.selection.style("background-color"), "rgb(255, 0, 0)");
      },
      "sets a property as a string": function(result) {
        assert.equal(result.selection.style("background-color"), "rgb(255, 0, 0)");
      },
      "sets a property as a function": function(result) {
        assert.equal(result.selection.style("color"), "rgb(0, 128, 0)");
      },
      "observes the specified priority": function(result) {
        var style = result.selection.node().style;
        assert.equal(style.getPropertyPriority("background-color"), "");
        assert.equal(style.getPropertyPriority("color"), "important");
      },
      "removes a property using a constant null": function(result) {
        assert.equal(result.selection.style("display"), "");
      },
      "removes a property using a function null": function(result) {
        assert.equal(result.selection.style("font-size"), "");
      }
    }
  };
  