Tests for transition.filter. #20

.eslintrc

@@ -11,3 +11,4 @@ extends:
 
 rules:
     no-cond-assign: 0
+    no-sparse-arrays: 0

test/transition/filter-test.js

@@ -0,0 +1,32 @@
+var tape = require("tape"),
+    jsdom = require("jsdom"),
+    d3_selection = require("d3-selection"),
+    d3_transition = require("../../");
+
+tape("transition.filter(selector) retains the elements matching the specified selector", function(test) {
+  var document = jsdom.jsdom("<h1 id='one'></h1><h1 id='two'></h1>"),
+      one = document.querySelector("#one"),
+      two = document.querySelector("#two"),
+      transition1 = d3_selection.selectAll([one, two]).data([1, 2]).transition().delay(function(d) { return d * 10; }),
+      transition2 = transition1.filter("#two");
+  test.equal(transition2 instanceof d3_transition.transition, true);
+  test.deepEqual(transition2._groups, [[, two]]);
+  test.equal(transition2._parents, transition1._parents);
+  test.equal(transition2._name, transition1._name);
+  test.equal(transition2._id, transition1._id);
+  test.end();
+});
+
+tape("transition.filter(function) retains the elements for which the specified function returns true", function(test) {
+  var document = jsdom.jsdom("<h1 id='one'></h1><h1 id='two'></h1>"),
+      one = document.querySelector("#one"),
+      two = document.querySelector("#two"),
+      transition1 = d3_selection.selectAll([one, two]).data([1, 2]).transition().delay(function(d) { return d * 10; }),
+      transition2 = transition1.filter(function() { return this === two; });
+  test.equal(transition2 instanceof d3_transition.transition, true);
+  test.deepEqual(transition2._groups, [[, two]]);
+  test.equal(transition2._parents, transition1._parents);
+  test.equal(transition2._name, transition1._name);
+  test.equal(transition2._id, transition1._id);
+  test.end();
+});