diff -r 000000000000 -r 6474c204b198 js/src/jit-test/tests/gc/incremental-state.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/jit-test/tests/gc/incremental-state.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,47 @@
+/*
+ * Test expected state changes during collection.
+ */
+
+if ("gcstate" in this) {
+    assertEq(gcstate(), "none");
+
+    /* Non-incremental GC. */
+    gc();
+    assertEq(gcstate(), "none");
+
+    /* Incremental GC in one slice. */
+    gcslice(1000000);
+    assertEq(gcstate(), "none");
+
+    /* 
+     * Incremental GC in multiple slices: if marking takes more than one slice,
+     * we yield before we start sweeping.
+     */
+    gcslice(1);
+    assertEq(gcstate(), "mark");
+    gcslice(1000000);
+    assertEq(gcstate(), "mark");
+    gcslice(1000000);
+    assertEq(gcstate(), "none");
+
+    /* Zeal mode 8: Incremental GC in two slices: 1) mark roots 2) finish collection. */
+    gczeal(8);
+    gcslice(1);
+    assertEq(gcstate(), "mark");
+    gcslice(1);
+    assertEq(gcstate(), "none");
+
+    /* Zeal mode 9: Incremental GC in two slices: 1) mark all 2) new marking and finish. */
+    gczeal(9);
+    gcslice(1);
+    assertEq(gcstate(), "mark");
+    gcslice(1);
+    assertEq(gcstate(), "none");
+
+    /* Zeal mode 10: Incremental GC in multiple slices (always yeilds before sweeping). */
+    gczeal(10);
+    gcslice(1000000);
+    assertEq(gcstate(), "sweep");
+    gcslice(1000000);
+    assertEq(gcstate(), "none");
+}