diff -r 000000000000 -r 6474c204b198 js/src/tests/ecma_6/Math/cbrt-approx.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/tests/ecma_6/Math/cbrt-approx.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,19 @@
+assertEq(Math.cbrt(1), 1);
+assertEq(Math.cbrt(-1), -1);
+
+var sloppy_tolerance = 200;  // FIXME
+
+assertNear(Math.cbrt(1e-300), 1e-100, sloppy_tolerance);
+assertNear(Math.cbrt(-1e-300), -1e-100, sloppy_tolerance);
+
+var cbrt_data = [
+    [ Math.E, 1.3956124250860895 ], 
+    [ Math.PI, 1.4645918875615231 ], 
+    [ Math.LN2, 0.8849970445005177 ], 
+    [ Math.SQRT2, 1.1224620483093728 ]
+];
+
+for (var [x, y] of cbrt_data)
+    assertNear(Math.cbrt(x), y, sloppy_tolerance);
+
+reportCompare(0, 0, "ok");