Test exponent notation format with fractionDigits argument specified.

test/format/format-test.js

@@ -65,6 +65,8 @@ suite.addBatch({
       assert.strictEqual(f(-42), "-4.2e+1");
       assert.strictEqual(f(-4200000), "-4.2e+6");
       assert.strictEqual(f(-42000000), "-4.2e+7");
+      assert.strictEqual(format(".0e")(42), "4e+1")
+      assert.strictEqual(format(".3e")(42), "4.200e+1")
     },
     "can output SI prefix notation": function(format) {
       var f = format("s");