diff --git a/test/env-assert.js b/test/env-assert.js
index 637503e2..d5ba00da 100644
--- a/test/env-assert.js
+++ b/test/env-assert.js
@@ -34,7 +34,7 @@ assert.hslEqual = function(actual, h, s, l, message) {
 
 assert.pathEqual = function(actual, expected, message) {
   if (!pathEqual(actual, expected)) {
-    assert.fail(actual, expected, message || "expected {expected}, got {actual}", null, assert.pathEqual);
+    assert.fail(formatPath(actual), formatPath(expected), message || "expected {expected}, got {actual}", null, assert.pathEqual);
   }
 };
 
@@ -57,16 +57,25 @@ function pathEqual(a, b) {
   return true;
 }
 
+var reNumber = /[-+]?(?:\d+\.\d+|\d+\.|\.\d+|\d+)(?:[eE][-]?\d+)?/g;
+
 function parsePath(path) {
-  var re = /[-+]?(?:\d+\.\d+|\d+\.|\.\d+|\d+)(?:[eE][-]?\d+)?/g, parts = [];
-  for (var i = 0, s0 = 0, s1, m; m = re.exec(path); ++i) {
+  var parts = [];
+  reNumber.lastIndex = 0;
+  for (var i = 0, s0 = 0, s1, m; m = reNumber.exec(path); ++i) {
     if (m.index) {
       var part = path.substring(s0, s1 = m.index);
       if (!/^[, ]$/.test(part)) parts.push(part);
     }
     parts.push(parseFloat(m[0]));
-    s0 = re.lastIndex;
+    s0 = reNumber.lastIndex;
   }
   if (s0 < path.length) parts.push(path.substring(s0));
   return parts;
 }
+
+function formatPath(path) {
+  return path.replace(reNumber, function(s) {
+    return Math.abs((s = +s) - Math.floor(s)) < 1e-6 ? Math.floor(s) : s.toFixed(6);
+  });
+}
diff --git a/test/svg/area-radial-test.js b/test/svg/area-radial-test.js
new file mode 100644
index 00000000..f21e8d04
--- /dev/null
+++ b/test/svg/area-radial-test.js
@@ -0,0 +1,200 @@
+require("../env");
+require("../../d3");
+
+var vows = require("vows"),
+    assert = require("assert");
+
+var suite = vows.describe("d3.svg.area.radial");
+
+suite.addBatch({
+  "area.radial": {
+    topic: function() {
+      return d3.svg.area.radial;
+    },
+
+    "radius is an alias for setting innerRadius and outerRadius": function(area) {
+      var a = area().radius(f);
+      function f() {}
+      assert.equal(a.radius(), f);
+      assert.equal(a.innerRadius(), f);
+      assert.equal(a.outerRadius(), f);
+    },
+    "radius is an alias for getting outerRadius": function(area) {
+      var a = area().outerRadius(f);
+      function f() {}
+      assert.equal(a.radius(), f);
+    },
+
+    "angle is an alias for setting startAngle and endAngle": function(area) {
+      var a = area().angle(f);
+      function f() {}
+      assert.equal(a.angle(), f);
+      assert.equal(a.startAngle(), f);
+      assert.equal(a.endAngle(), f);
+    },
+    "angle is an alias for getting endAngle": function(area) {
+      var a = area().endAngle(f);
+      function f() {}
+      assert.equal(a.angle(), f);
+    },
+
+    "innerRadius defaults to a function accessor": function(area) {
+      var a = area();
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-10L0,-20L0,-20L0,-10Z");
+      assert.typeOf(a.innerRadius(), "function");
+    },
+    "innerRadius can be defined as a constant": function(area) {
+      var a = area().innerRadius(30);
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-30L0,-30L0,-30L0,-30Z");
+      assert.equal(a.innerRadius(), 30);
+    },
+    "innerRadius can be defined as a function": function(area) {
+      var a = area().innerRadius(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return 30; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-30L0,-30L0,-30L0,-30Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+
+    "outerRadius defaults to a function accessor": function(area) {
+      var a = area();
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-10L0,-20L0,-20L0,-10Z");
+      assert.typeOf(a.outerRadius(), "function");
+    },
+    "outerRadius can be defined as a constant": function(area) {
+      var a = area().outerRadius(30);
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-30L25.244130,-16.209069L27.278923,12.484405L4.233600,29.699775L0,-10L0,-20L0,-20L0,-10Z");
+      assert.equal(a.outerRadius(), 30);
+    },
+    "outerRadius can be defined as a function": function(area) {
+      var a = area().outerRadius(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return 30; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-30L25.244130,-16.209069L27.278923,12.484405L4.233600,29.699775L0,-10L0,-20L0,-20L0,-10Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+
+    "startAngle defaults to zero": function(area) {
+      var a = area();
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-10L0,-20L0,-20L0,-10Z");
+      assert.equal(a.startAngle(), 0);
+    },
+    "startAngle can be defined as a constant": function(area) {
+      var a = area().startAngle(Math.PI / 2);
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L10,0L20,0L20,0L10,0Z");
+      assert.equal(a.startAngle(), Math.PI / 2);
+    },
+    "startAngle can be defined as a function": function(area) {
+      var a = area().startAngle(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return Math.PI / 2; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L10,0L20,0L20,0L10,0Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+
+    "endAngle defaults to a function accessor": function(area) {
+      var a = area();
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-10L16.829420,-10.806046L18.185949,8.322937L1.411200,9.899925L0,-10L0,-20L0,-20L0,-10Z");
+      assert.typeOf(a.endAngle(), "function");
+    },
+    "endAngle can be defined as a constant": function(area) {
+      var a = area().endAngle(Math.PI / 2);
+      assert.pathEqual(a([[10, 0], [20, 1], [20, 2], [10, 3]]), "M10,0L20,0L20,0L10,0L0,-10L0,-20L0,-20L0,-10Z");
+      assert.equal(a.endAngle(), Math.PI / 2);
+    },
+    "endAngle can be defined as a function": function(area) {
+      var a = area().endAngle(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return Math.PI / 2; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M10,0L20,0L20,0L10,0L0,-10L0,-20L0,-20L0,-10Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+
+    "if innerRadius === outerRadius, radius is only evaluated once per point": function(area) {
+      var a = area().radius(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return 30; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M0,-30L25.244130,-16.209069L27.278923,12.484405L4.233600,29.699775L0,-30L0,-30L0,-30L0,-30Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+    "if startAngle === endAngle, angle is only evaluated once per point": function(area) {
+      var a = area().angle(f), t = {}, dd = [], ii = [], tt = [];
+      function f(d, i) { dd.push(d); ii.push(i); tt.push(this); return Math.PI / 2; }
+      assert.pathEqual(a.call(t, [[10, 0], [20, 1], [20, 2], [10, 3]]), "M10,0L20,0L20,0L10,0L10,0L20,0L20,0L10,0Z");
+      assert.deepEqual(dd, [[10, 0], [20, 1], [20, 2], [10, 3]], "expected data, got {actual}");
+      assert.deepEqual(ii, [0, 1, 2, 3], "expected index, got {actual}");
+      assert.deepEqual(tt, [t, t, t, t], "expected this, got {actual}");
+    },
+
+    "interpolate defaults to linear": function(area) {
+      assert.equal(area().interpolate(), "linear");
+    },
+    "interpolate can be defined as a constant": function(area) {
+      var a = area().interpolate("step-before");
+      assert.pathEqual(a([[0, 0], [1, 1]]), "M0,0V-0.540302H0.841471L0,-1V0H0Z");
+      assert.equal(a.interpolate(), "step-before");
+    },
+
+    "tension defaults to .7": function(area) {
+      assert.equal(area().tension(), .7);
+    },
+    "tension can be specified as a constant": function(area) {
+      var a = area().tension(.5);
+      assert.equal(a.tension(), .5);
+    },
+
+    "returns null if input points array is empty": function(area) {
+      assert.isNull(area()([]));
+    },
+
+    "interpolate(linear)": {
+      "supports linear interpolation": testInterpolation("linear")
+    },
+
+    "interpolate(step)": {
+      "supports step-before interpolation": testInterpolation("step-before"),
+      "supports step-after interpolation": testInterpolation("step-after")
+    },
+
+    "interpolate(basis)": {
+      "supports basis interpolation": testInterpolation("basis"),
+      "supports basis-open interpolation": testInterpolation("basis-open")
+    },
+
+    "interpolate(cardinal)": {
+      "supports cardinal interpolation": testInterpolation("cardinal"),
+      "supports cardinal-open interpolation": testInterpolation("cardinal-open")
+    },
+
+    "interpolate(monotone)": {
+      "supports monotone interpolation": testInterpolation("monotone")
+    }
+  }
+});
+
+// A radial area is just a transformation of a Cartesian line.
+function testInterpolation(interpolate) {
+  var data = [[10, 0], [20, 1], [20, 2], [10, 3]];
+
+  var radial = d3.svg.area.radial()
+      .innerRadius(function(d) { return d[0]; })
+      .outerRadius(function(d) { return d[0] * 2; })
+      .angle(function(d) { return d[1]; });
+
+  var cartesian = d3.svg.area()
+      .x0(function(d) { return d[0] * Math.cos(d[1] - Math.PI / 2); })
+      .x1(function(d) { return 2 * d[0] * Math.cos(d[1] - Math.PI / 2); })
+      .y0(function(d) { return d[0] * Math.sin(d[1] - Math.PI / 2); })
+      .y1(function(d) { return 2 * d[0] * Math.sin(d[1] - Math.PI / 2); });
+
+  return function() {
+    assert.pathEqual(radial.interpolate(interpolate)(data), cartesian.interpolate(interpolate)(data));
+  };
+}
+
+suite.export(module);
diff --git a/test/svg/area-test.js b/test/svg/area-test.js
index 2d047fb2..706ba9b9 100644
--- a/test/svg/area-test.js
+++ b/test/svg/area-test.js
@@ -135,17 +135,17 @@ suite.addBatch({
       assert.equal(area().interpolate(), "linear");
     },
     "interpolate can be defined as a constant": function(area) {
-      var l = area().interpolate("step-before");
-      assert.pathEqual(l([[0, 0], [1, 1]]), "M0,0V1H1L1,0V0H0Z");
-      assert.equal(l.interpolate(), "step-before");
+      var a = area().interpolate("step-before");
+      assert.pathEqual(a([[0, 0], [1, 1]]), "M0,0V1H1L1,0V0H0Z");
+      assert.equal(a.interpolate(), "step-before");
     },
 
     "tension defaults to .7": function(area) {
       assert.equal(area().tension(), .7);
     },
     "tension can be specified as a constant": function(area) {
-      var l = area().tension(.5);
-      assert.equal(l.tension(), .5);
+      var a = area().tension(.5);
+      assert.equal(a.tension(), .5);
     },
 
     "returns null if input points array is empty": function(area) {
diff --git a/test/svg/line-radial-test.js b/test/svg/line-radial-test.js
index 96c68491..9e0855a6 100644
--- a/test/svg/line-radial-test.js
+++ b/test/svg/line-radial-test.js
@@ -111,12 +111,14 @@ suite.addBatch({
 function testInterpolation(interpolate) {
   var data = [[10, 0], [20, 1], [20, 2], [10, 3]];
 
+  var radial = d3.svg.line.radial();
+
   var cartesian = d3.svg.line()
       .x(function(d) { return d[0] * Math.cos(d[1] - Math.PI / 2); })
       .y(function(d) { return d[0] * Math.sin(d[1] - Math.PI / 2); });
 
-  return function(line) {
-    assert.pathEqual(line().interpolate(interpolate)(data), cartesian.interpolate(interpolate)(data));
+  return function() {
+    assert.pathEqual(radial.interpolate(interpolate)(data), cartesian.interpolate(interpolate)(data));
   };
 }