diff --git a/test/core/format-test.js b/test/core/format-test.js
new file mode 100644
index 00000000..e0792dd8
--- /dev/null
+++ b/test/core/format-test.js
@@ -0,0 +1,200 @@
+require("../env");
+require("../../d3");
+
+var vows = require("vows"),
+    assert = require("assert");
+
+var suite = vows.describe("d3.format");
+
+suite.addBatch({
+  "format": {
+    topic: function() {
+      return d3.format;
+    },
+    "returns a string": function(format) {
+      assert.isString(format("d")(0));
+    },
+    "can zero fill": function(format) {
+      var f = format("08d");
+      assert.strictEqual(f(0), "00000000");
+      assert.strictEqual(f(42), "00000042");
+      assert.strictEqual(f(42000000), "42000000");
+      assert.strictEqual(f(420000000), "420000000");
+      assert.strictEqual(f(-4), "−0000004");
+      assert.strictEqual(f(-42), "−0000042");
+      assert.strictEqual(f(-4200000), "−4200000");
+      assert.strictEqual(f(-42000000), "−42000000");
+    },
+    "can space fill": function(format) {
+      var f = format("8d");
+      assert.strictEqual(f(0), "       0");
+      assert.strictEqual(f(42), "      42");
+      assert.strictEqual(f(42000000), "42000000");
+      assert.strictEqual(f(420000000), "420000000");
+      assert.strictEqual(f(-4), "      −4");
+      assert.strictEqual(f(-42), "     −42");
+      assert.strictEqual(f(-4200000), "−4200000");
+      assert.strictEqual(f(-42000000), "−42000000");
+    },
+    "can output fixed-point notation": function(format) {
+      assert.strictEqual(format(".1f")(0.49), "0.5");
+      assert.strictEqual(format(".2f")(0.449), "0.45");
+      assert.strictEqual(format(".3f")(0.4449), "0.445");
+      assert.strictEqual(format(".5f")(0.444449), "0.44445");
+      assert.strictEqual(format(".1f")(100), "100.0");
+      assert.strictEqual(format(".2f")(100), "100.00");
+      assert.strictEqual(format(".3f")(100), "100.000");
+      assert.strictEqual(format(".5f")(100), "100.00000");
+    },
+    "can output general notation": function(format) {
+      assert.strictEqual(format(".1g")(0.049), "0.05");
+      assert.strictEqual(format(".1g")(0.49), "0.5");
+      assert.strictEqual(format(".2g")(0.449), "0.45");
+      assert.strictEqual(format(".3g")(0.4449), "0.445");
+      assert.strictEqual(format(".5g")(0.444449), "0.44445");
+      assert.strictEqual(format(".1g")(100), "1e+2");
+      assert.strictEqual(format(".2g")(100), "1.0e+2");
+      assert.strictEqual(format(".3g")(100), "100");
+      assert.strictEqual(format(".5g")(100), "100.00");
+      assert.strictEqual(format(".5g")(100.2), "100.20");
+      assert.strictEqual(format(".2g")(0.002), "0.0020");
+    },
+    "can output exponent notation ": function(format) {
+      var f = format("e");
+      assert.strictEqual(f(0), "0e+0");
+      assert.strictEqual(f(42), "4.2e+1");
+      assert.strictEqual(f(42000000), "4.2e+7");
+      assert.strictEqual(f(420000000), "4.2e+8");
+      assert.strictEqual(f(-4), "−4e+0");
+      assert.strictEqual(f(-42), "−4.2e+1");
+      assert.strictEqual(f(-4200000), "−4.2e+6");
+      assert.strictEqual(f(-42000000), "−4.2e+7");
+    },
+    "can output a percentage": function(format) {
+      var f = format("%");
+      assert.strictEqual(f(0), "0%");
+      assert.strictEqual(f(.042), "4%");
+      assert.strictEqual(f(.42), "42%");
+      assert.strictEqual(f(4.2), "420%");
+      assert.strictEqual(f(-.042), "−4%");
+      assert.strictEqual(f(-.42), "−42%");
+      assert.strictEqual(f(-4.2), "−420%");
+    },
+    "can output a percentage with rounding and sign": function(format) {
+      var f = format("+.2p");
+      assert.strictEqual(f(.00123), "+0.12%");
+      assert.strictEqual(f(.0123), "+1.2%");
+      assert.strictEqual(f(.123), "+12%");
+      assert.strictEqual(f(1.23), "+120%");
+      assert.strictEqual(f(-.00123), "−0.12%");
+      assert.strictEqual(f(-.0123), "−1.2%");
+      assert.strictEqual(f(-.123), "−12%");
+      assert.strictEqual(f(-1.23), "−120%");
+    },
+    "can round to significant digits": function(format) {
+      assert.strictEqual(format(".1r")(0.049), "0.05");
+      assert.strictEqual(format(".1r")(0.49), "0.5");
+      assert.strictEqual(format(".2r")(0.449), "0.45");
+      assert.strictEqual(format(".3r")(0.4449), "0.445");
+      assert.strictEqual(format(".5r")(0.444449), "0.44445");
+      assert.strictEqual(format("r")(123.45), "123");
+      assert.strictEqual(format(".1r")(123.45), "100");
+      assert.strictEqual(format(".2r")(123.45), "120");
+      assert.strictEqual(format(".3r")(123.45), "123");
+      assert.strictEqual(format(".4r")(123.45), "123.5");
+      assert.strictEqual(format(".5r")(123.45), "123.45");
+      assert.strictEqual(format(".6r")(123.45), "123.450");
+    },
+    "can group thousands": function(format) {
+      var f = format(",d");
+      assert.strictEqual(f(0), "0");
+      assert.strictEqual(f(42), "42");
+      assert.strictEqual(f(42000000), "42,000,000");
+      assert.strictEqual(f(420000000), "420,000,000");
+      assert.strictEqual(f(-4), "−4");
+      assert.strictEqual(f(-42), "−42");
+      assert.strictEqual(f(-4200000), "−4,200,000");
+      assert.strictEqual(f(-42000000), "−42,000,000");
+    },
+    "can group thousands and zero fill": function(format) {
+      assert.strictEqual(format("01,d")(0), "0");
+      assert.strictEqual(format("01,d")(0), "0");
+      assert.strictEqual(format("02,d")(0), "00");
+      assert.strictEqual(format("03,d")(0), "000");
+      assert.strictEqual(format("05,d")(0), "0,000");
+      assert.strictEqual(format("08,d")(0), "0,000,000");
+      assert.strictEqual(format("013,d")(0), "0,000,000,000");
+      assert.strictEqual(format("021,d")(0), "0,000,000,000,000,000");
+    },
+    "can group thousands and zero fill with overflow": function(format) {
+      assert.strictEqual(format("01,d")(1), "1");
+      assert.strictEqual(format("01,d")(1), "1");
+      assert.strictEqual(format("02,d")(12), "12");
+      assert.strictEqual(format("03,d")(123), "123");
+      assert.strictEqual(format("05,d")(12345), "12,345");
+      assert.strictEqual(format("08,d")(12345678), "12,345,678");
+      assert.strictEqual(format("013,d")(1234567890123), "1,234,567,890,123");
+    },
+    "can group thousands and space fill": function(format) {
+      assert.strictEqual(format("1,d")(0), "0");
+      assert.strictEqual(format("1,d")(0), "0");
+      assert.strictEqual(format("2,d")(0), " 0");
+      assert.strictEqual(format("3,d")(0), "  0");
+      assert.strictEqual(format("5,d")(0), "    0");
+      assert.strictEqual(format("8,d")(0), "       0");
+      assert.strictEqual(format("13,d")(0), "            0");
+      assert.strictEqual(format("21,d")(0), "                    0");
+    },
+    "can group thousands and space fill with overflow": function(format) {
+      assert.strictEqual(format("1,d")(1), "1");
+      assert.strictEqual(format("1,d")(1), "1");
+      assert.strictEqual(format("2,d")(12), "12");
+      assert.strictEqual(format("3,d")(123), "123");
+      assert.strictEqual(format("5,d")(12345), "12,345");
+      assert.strictEqual(format("8,d")(12345678), "12,345,678");
+      assert.strictEqual(format("13,d")(1234567890123), "1,234,567,890,123");
+    },
+    "can group thousands with general notation": function(format) {
+      var f = format(",g");
+      assert.strictEqual(f(0), "0");
+      assert.strictEqual(f(42), "42");
+      assert.strictEqual(f(42000000), "42,000,000");
+      assert.strictEqual(f(420000000), "420,000,000");
+      assert.strictEqual(f(-4), "−4");
+      assert.strictEqual(f(-42), "−42");
+      assert.strictEqual(f(-4200000), "−4,200,000");
+      assert.strictEqual(f(-42000000), "−42,000,000");
+    },
+    "can group thousands, space fill, and round to significant digits": function(format) {
+      assert.strictEqual(format("10,.1f")(123456.49), " 123,456.5");
+      assert.strictEqual(format("10,.2f")(1234567.449), "1,234,567.45");
+      assert.strictEqual(format("10,.3f")(12345678.4449), "12,345,678.445");
+      assert.strictEqual(format("10,.5f")(123456789.444449), "123,456,789.44445");
+      assert.strictEqual(format("10,.1f")(123456), " 123,456.0");
+      assert.strictEqual(format("10,.2f")(1234567), "1,234,567.00");
+      assert.strictEqual(format("10,.3f")(12345678), "12,345,678.000");
+      assert.strictEqual(format("10,.5f")(123456789), "123,456,789.00000");
+    },
+    "can display integers in fixed-point notation": function(format) {
+      assert.strictEqual(format("f")(42), "42");
+    },
+    "will not display non-integers in integer format": function(format) {
+      assert.strictEqual(format("d")(4.2), "");
+    },
+    "supports \"n\" as an alias for \",g\"": function(format) {
+      var f = format("n");
+      assert.strictEqual(f(.0042), "0.0042");
+      assert.strictEqual(f(.42), "0.42");
+      assert.strictEqual(f(0), "0");
+      assert.strictEqual(f(42), "42");
+      assert.strictEqual(f(42000000), "42,000,000");
+      assert.strictEqual(f(420000000), "420,000,000");
+      assert.strictEqual(f(-4), "−4");
+      assert.strictEqual(f(-42), "−42");
+      assert.strictEqual(f(-4200000), "−4,200,000");
+      assert.strictEqual(f(-42000000), "−42,000,000");
+    }
+  }
+});
+
+suite.export(module);
diff --git a/test/core/test-format.js b/test/core/test-format.js
deleted file mode 100644
index c14beff7..00000000
--- a/test/core/test-format.js
+++ /dev/null
@@ -1,194 +0,0 @@
-require("./../../lib/env-js/envjs/node");
-require("./../../d3");
-
-console.log("zero fill:");
-console.log("  ", d3.format("08d")(0));
-console.log("  ", d3.format("08d")(42));
-console.log("  ", d3.format("08d")(42000000));
-console.log("  ", d3.format("08d")(420000000));
-console.log("  ", d3.format("08d")(-4));
-console.log("  ", d3.format("08d")(-42));
-console.log("  ", d3.format("08d")(-4200000));
-console.log("  ", d3.format("08d")(-42000000));
-console.log("");
-
-console.log("space fill:");
-console.log("  ", d3.format("8d")(0));
-console.log("  ", d3.format("8d")(42));
-console.log("  ", d3.format("8d")(42000000));
-console.log("  ", d3.format("8d")(420000000));
-console.log("  ", d3.format("8d")(-4));
-console.log("  ", d3.format("8d")(-42));
-console.log("  ", d3.format("8d")(-4200000));
-console.log("  ", d3.format("8d")(-42000000));
-console.log("");
-
-// TODO fill with other characters (requires align support)
-
-console.log("grouping:");
-console.log("  ", d3.format(",d")(0));
-console.log("  ", d3.format(",d")(42));
-console.log("  ", d3.format(",d")(42000000));
-console.log("  ", d3.format(",d")(420000000));
-console.log("  ", d3.format(",d")(-4));
-console.log("  ", d3.format(",d")(-42));
-console.log("  ", d3.format(",d")(-4200000));
-console.log("  ", d3.format(",d")(-42000000));
-console.log("");
-
-console.log("grouping with zero fill:");
-console.log("  ", d3.format("01,d")(0));
-console.log("  ", d3.format("01,d")(0));
-console.log("  ", d3.format("02,d")(0));
-console.log("  ", d3.format("03,d")(0));
-console.log("  ", d3.format("05,d")(0));
-console.log("  ", d3.format("08,d")(0));
-console.log("  ", d3.format("013,d")(0));
-console.log("  ", d3.format("021,d")(0));
-console.log("");
-
-console.log("grouping with zero fill (overflow):");
-console.log("  ", d3.format("01,d")(1));
-console.log("  ", d3.format("01,d")(1));
-console.log("  ", d3.format("02,d")(12));
-console.log("  ", d3.format("03,d")(123));
-console.log("  ", d3.format("05,d")(12345));
-console.log("  ", d3.format("08,d")(12345678));
-console.log("  ", d3.format("013,d")(1234567890123));
-console.log("");
-
-console.log("grouping with space fill:");
-console.log("  ", d3.format("1,d")(0));
-console.log("  ", d3.format("1,d")(0));
-console.log("  ", d3.format("2,d")(0));
-console.log("  ", d3.format("3,d")(0));
-console.log("  ", d3.format("5,d")(0));
-console.log("  ", d3.format("8,d")(0));
-console.log("  ", d3.format("13,d")(0));
-console.log("  ", d3.format("21,d")(0));
-console.log("");
-
-console.log("grouping with space fill (overflow):");
-console.log("  ", d3.format("1,d")(1));
-console.log("  ", d3.format("1,d")(1));
-console.log("  ", d3.format("2,d")(12));
-console.log("  ", d3.format("3,d")(123));
-console.log("  ", d3.format("5,d")(12345));
-console.log("  ", d3.format("8,d")(12345678));
-console.log("  ", d3.format("13,d")(1234567890123));
-console.log("");
-
-console.log("grouping with general notation:");
-console.log("  ", d3.format(",g")(0));
-console.log("  ", d3.format(",g")(42));
-console.log("  ", d3.format(",g")(42000000));
-console.log("  ", d3.format(",g")(420000000));
-console.log("  ", d3.format(",g")(-4));
-console.log("  ", d3.format(",g")(-42));
-console.log("  ", d3.format(",g")(-4200000));
-console.log("  ", d3.format(",g")(-42000000));
-console.log("");
-
-console.log("precision (fixed-point notation):");
-console.log("  ", d3.format(".1f")(0.49));
-console.log("  ", d3.format(".2f")(0.449));
-console.log("  ", d3.format(".3f")(0.4449));
-console.log("  ", d3.format(".5f")(0.444449));
-console.log("  ", d3.format(".1f")(100));
-console.log("  ", d3.format(".2f")(100));
-console.log("  ", d3.format(".3f")(100));
-console.log("  ", d3.format(".5f")(100));
-console.log("");
-
-console.log("precision (significant digits):");
-console.log("  ", d3.format(".1g")(0.049));
-console.log("  ", d3.format(".1g")(0.49));
-console.log("  ", d3.format(".2g")(0.449));
-console.log("  ", d3.format(".3g")(0.4449));
-console.log("  ", d3.format(".5g")(0.444449));
-console.log("  ", d3.format(".1g")(100));
-console.log("  ", d3.format(".2g")(100));
-console.log("  ", d3.format(".3g")(100));
-console.log("  ", d3.format(".5g")(100));
-console.log("  ", d3.format(".5g")(100.2));
-console.log("  ", d3.format(".2g")(0.002));
-console.log("");
-
-console.log("precision and rounding (significant digits):");
-console.log("  ", d3.format(".1r")(0.049));
-console.log("  ", d3.format(".1r")(0.49));
-console.log("  ", d3.format(".2r")(0.449));
-console.log("  ", d3.format(".3r")(0.4449));
-console.log("  ", d3.format(".5r")(0.444449));
-console.log("  ", d3.format("r")(123.45));
-console.log("  ", d3.format(".1r")(123.45));
-console.log("  ", d3.format(".2r")(123.45));
-console.log("  ", d3.format(".3r")(123.45));
-console.log("  ", d3.format(".4r")(123.45));
-console.log("  ", d3.format(".5r")(123.45));
-console.log("  ", d3.format(".6r")(123.45));
-console.log("");
-
-console.log("precision and grouping with space fill:");
-console.log("  ", d3.format("10,.1f")(123456.49));
-console.log("  ", d3.format("10,.2f")(1234567.449));
-console.log("  ", d3.format("10,.3f")(12345678.4449));
-console.log("  ", d3.format("10,.5f")(123456789.444449));
-console.log("  ", d3.format("10,.1f")(123456));
-console.log("  ", d3.format("10,.2f")(1234567));
-console.log("  ", d3.format("10,.3f")(12345678));
-console.log("  ", d3.format("10,.5f")(123456789));
-console.log("");
-
-console.log("float type passed int:");
-console.log("  ", d3.format("f")(42));
-console.log("");
-
-console.log("int type passed float:");
-console.log(d3.format("d")(4.2));
-console.log("");
-
-console.log("number:");
-console.log("  ", d3.format("n")(.0042));
-console.log("  ", d3.format("n")(.42));
-console.log("  ", d3.format("n")(0));
-console.log("  ", d3.format("n")(42));
-console.log("  ", d3.format("n")(42000000));
-console.log("  ", d3.format("n")(420000000));
-console.log("  ", d3.format("n")(-4));
-console.log("  ", d3.format("n")(-42));
-console.log("  ", d3.format("n")(-4200000));
-console.log("  ", d3.format("n")(-42000000));
-console.log("");
-
-console.log("percentage:");
-console.log("  ", d3.format("%")(0));
-console.log("  ", d3.format("%")(.042));
-console.log("  ", d3.format("%")(.42));
-console.log("  ", d3.format("%")(4.2));
-console.log("  ", d3.format("%")(-.042));
-console.log("  ", d3.format("%")(-.42));
-console.log("  ", d3.format("%")(-4.2));
-console.log("");
-
-console.log("percentage with rounding and sign:");
-console.log("  ", d3.format("+.2p")(.00123));
-console.log("  ", d3.format("+.2p")(.0123));
-console.log("  ", d3.format("+.2p")(.123));
-console.log("  ", d3.format("+.2p")(1.23));
-console.log("  ", d3.format("+.2p")(-.00123));
-console.log("  ", d3.format("+.2p")(-.0123));
-console.log("  ", d3.format("+.2p")(-.123));
-console.log("  ", d3.format("+.2p")(-1.23));
-console.log("");
-
-console.log("exponent:");
-console.log("  ", d3.format("e")(0));
-console.log("  ", d3.format("e")(42));
-console.log("  ", d3.format("e")(42000000));
-console.log("  ", d3.format("e")(420000000));
-console.log("  ", d3.format("e")(-4));
-console.log("  ", d3.format("e")(-42));
-console.log("  ", d3.format("e")(-4200000));
-console.log("  ", d3.format("e")(-42000000));
-console.log("");
diff --git a/test/core/test-format.out b/test/core/test-format.out
deleted file mode 100644
index 8d6b7cf6..00000000
--- a/test/core/test-format.out
+++ /dev/null
@@ -1,172 +0,0 @@
-zero fill:
-   00000000
-   00000042
-   42000000
-   420000000
-   −0000004
-   −0000042
-   −4200000
-   −42000000
-
-space fill:
-          0
-         42
-   42000000
-   420000000
-         −4
-        −42
-   −4200000
-   −42000000
-
-grouping:
-   0
-   42
-   42,000,000
-   420,000,000
-   −4
-   −42
-   −4,200,000
-   −42,000,000
-
-grouping with zero fill:
-   0
-   0
-   00
-   000
-   0,000
-   0,000,000
-   0,000,000,000
-   0,000,000,000,000,000
-
-grouping with zero fill (overflow):
-   1
-   1
-   12
-   123
-   12,345
-   12,345,678
-   1,234,567,890,123
-
-grouping with space fill:
-   0
-   0
-    0
-     0
-       0
-          0
-               0
-                       0
-
-grouping with space fill (overflow):
-   1
-   1
-   12
-   123
-   12,345
-   12,345,678
-   1,234,567,890,123
-
-grouping with general notation:
-   0
-   42
-   42,000,000
-   420,000,000
-   −4
-   −42
-   −4,200,000
-   −42,000,000
-
-precision (fixed-point notation):
-   0.5
-   0.45
-   0.445
-   0.44445
-   100.0
-   100.00
-   100.000
-   100.00000
-
-precision (significant digits):
-   0.05
-   0.5
-   0.45
-   0.445
-   0.44445
-   1e+2
-   1.0e+2
-   100
-   100.00
-   100.20
-   0.0020
-
-precision and rounding (significant digits):
-   0.05
-   0.5
-   0.45
-   0.445
-   0.44445
-   123
-   100
-   120
-   123
-   123.5
-   123.45
-   123.450
-
-precision and grouping with space fill:
-    123,456.5
-   1,234,567.45
-   12,345,678.445
-   123,456,789.44445
-    123,456.0
-   1,234,567.00
-   12,345,678.000
-   123,456,789.00000
-
-float type passed int:
-   42
-
-int type passed float:
-
-
-number:
-   0.0042
-   0.42
-   0
-   42
-   42,000,000
-   420,000,000
-   −4
-   −42
-   −4,200,000
-   −42,000,000
-
-percentage:
-   0%
-   4%
-   42%
-   420%
-   −4%
-   −42%
-   −420%
-
-percentage with rounding and sign:
-   +0.12%
-   +1.2%
-   +12%
-   +120%
-   −0.12%
-   −1.2%
-   −12%
-   −120%
-
-exponent:
-   0e+0
-   4.2e+1
-   4.2e+7
-   4.2e+8
-   −4e+0
-   −4.2e+1
-   −4.2e+6
-   −4.2e+7
-