diff --git a/TODO b/TODO
index 27ff8688d..c93b33e62 100644
--- a/TODO
+++ b/TODO
@@ -85,8 +85,6 @@ Tests to write:
 
 - GObject, FreeType, etc
 
-- hb_set_t
-
 - hb_cache_t and relatives
 
 - hb_feature_to/from_string
diff --git a/src/hb-set-private.hh b/src/hb-set-private.hh
index c736b6993..8e03d681a 100644
--- a/src/hb-set-private.hh
+++ b/src/hb-set-private.hh
@@ -137,6 +137,7 @@ struct hb_set_t
 {
   hb_object_header_t header;
   ASSERT_POD ();
+  bool in_error;
 
   inline void init (void) {
     header.init ();
@@ -224,6 +225,11 @@ struct hb_set_t
     for (unsigned int i = 0; i < ELTS; i++)
       elts[i] ^= other->elts[i];
   }
+  inline void invert (void)
+  {
+    for (unsigned int i = 0; i < ELTS; i++)
+      elts[i] = ~elts[i];
+  }
   inline bool next (hb_codepoint_t *codepoint) const
   {
     if (unlikely (*codepoint == SENTINEL)) {
diff --git a/src/hb-set.cc b/src/hb-set.cc
index 93f983aeb..5f427a5d8 100644
--- a/src/hb-set.cc
+++ b/src/hb-set.cc
@@ -49,6 +49,7 @@ hb_set_get_empty (void)
 {
   static const hb_set_t _hb_set_nil = {
     HB_OBJECT_HEADER_STATIC,
+    true, /* in_error */
 
     {0} /* elts */
   };
@@ -93,7 +94,7 @@ hb_set_get_user_data (hb_set_t           *set,
 hb_bool_t
 hb_set_allocation_successful (const hb_set_t  *set HB_UNUSED)
 {
-  return true;
+  return !set->in_error;
 }
 
 void
@@ -187,6 +188,12 @@ hb_set_symmetric_difference (hb_set_t       *set,
   set->symmetric_difference (other);
 }
 
+void
+hb_set_invert (hb_set_t *set)
+{
+  set->invert ();
+}
+
 unsigned int
 hb_set_get_population (const hb_set_t *set)
 {
diff --git a/src/hb-set.h b/src/hb-set.h
index ec3d119e1..291e24974 100644
--- a/src/hb-set.h
+++ b/src/hb-set.h
@@ -121,6 +121,9 @@ void
 hb_set_symmetric_difference (hb_set_t       *set,
 			     const hb_set_t *other);
 
+void
+hb_set_invert (hb_set_t *set);
+
 unsigned int
 hb_set_get_population (const hb_set_t *set);
 
diff --git a/test/api/Makefile.am b/test/api/Makefile.am
index c5a015fed..237f92c88 100644
--- a/test/api/Makefile.am
+++ b/test/api/Makefile.am
@@ -21,6 +21,7 @@ TEST_PROGS = \
 	test-common \
 	test-font \
 	test-object \
+	test-set \
 	test-shape \
 	test-unicode \
 	test-version \
diff --git a/test/api/test-set.c b/test/api/test-set.c
new file mode 100644
index 000000000..f59760d83
--- /dev/null
+++ b/test/api/test-set.c
@@ -0,0 +1,312 @@
+/*
+ * Copyright © 2013  Google, Inc.
+ *
+ *  This is part of HarfBuzz, a text shaping library.
+ *
+ * Permission is hereby granted, without written agreement and without
+ * license or royalty fees, to use, copy, modify, and distribute this
+ * software and its documentation for any purpose, provided that the
+ * above copyright notice and the following two paragraphs appear in
+ * all copies of this software.
+ *
+ * IN NO EVENT SHALL THE COPYRIGHT HOLDER BE LIABLE TO ANY PARTY FOR
+ * DIRECT, INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES
+ * ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION, EVEN
+ * IF THE COPYRIGHT HOLDER HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH
+ * DAMAGE.
+ *
+ * THE COPYRIGHT HOLDER SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING,
+ * BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
+ * FITNESS FOR A PARTICULAR PURPOSE.  THE SOFTWARE PROVIDED HEREUNDER IS
+ * ON AN "AS IS" BASIS, AND THE COPYRIGHT HOLDER HAS NO OBLIGATION TO
+ * PROVIDE MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.
+ *
+ * Google Author(s): Behdad Esfahbod
+ */
+
+#include "hb-test.h"
+
+/* Unit tests for hb-set.h */
+
+
+#if 0
+static void
+test_buffer_properties (fixture_t *fixture, gconstpointer user_data)
+{
+  hb_buffer_t *b = fixture->buffer;
+  hb_unicode_funcs_t *ufuncs;
+
+  /* test default properties */
+
+  g_assert (hb_buffer_get_unicode_funcs (b) == hb_unicode_funcs_get_default ());
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_INVALID);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_INVALID);
+  g_assert (hb_buffer_get_language (b) == NULL);
+  g_assert (hb_buffer_get_flags (b) == HB_BUFFER_FLAGS_DEFAULT);
+
+
+  /* test property changes are retained */
+  ufuncs = hb_unicode_funcs_create (NULL);
+  hb_buffer_set_unicode_funcs (b, ufuncs);
+  hb_unicode_funcs_destroy (ufuncs);
+  g_assert (hb_buffer_get_unicode_funcs (b) == ufuncs);
+
+  hb_buffer_set_direction (b, HB_DIRECTION_RTL);
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_RTL);
+
+  hb_buffer_set_script (b, HB_SCRIPT_ARABIC);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_ARABIC);
+
+  hb_buffer_set_language (b, hb_language_from_string ("fa", -1));
+  g_assert (hb_buffer_get_language (b) == hb_language_from_string ("Fa", -1));
+
+  hb_buffer_set_flags (b, HB_BUFFER_FLAG_BOT);
+  g_assert (hb_buffer_get_flags (b) == HB_BUFFER_FLAG_BOT);
+
+
+
+  /* test clear clears all properties but unicode_funcs */
+
+  hb_buffer_clear (b);
+
+  g_assert (hb_buffer_get_unicode_funcs (b) == ufuncs);
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_INVALID);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_INVALID);
+  g_assert (hb_buffer_get_language (b) == NULL);
+  g_assert (hb_buffer_get_flags (b) == HB_BUFFER_FLAGS_DEFAULT);
+
+
+  /* test reset clears all properties */
+
+  hb_buffer_set_direction (b, HB_DIRECTION_RTL);
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_RTL);
+
+  hb_buffer_set_script (b, HB_SCRIPT_ARABIC);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_ARABIC);
+
+  hb_buffer_set_language (b, hb_language_from_string ("fa", -1));
+  g_assert (hb_buffer_get_language (b) == hb_language_from_string ("Fa", -1));
+
+  hb_buffer_set_flags (b, HB_BUFFER_FLAG_BOT);
+  g_assert (hb_buffer_get_flags (b) == HB_BUFFER_FLAG_BOT);
+
+  hb_buffer_reset (b);
+
+  g_assert (hb_buffer_get_unicode_funcs (b) == hb_unicode_funcs_get_default ());
+  g_assert (hb_buffer_get_direction (b) == HB_DIRECTION_INVALID);
+  g_assert (hb_buffer_get_script (b) == HB_SCRIPT_INVALID);
+  g_assert (hb_buffer_get_language (b) == NULL);
+  g_assert (hb_buffer_get_flags (b) == HB_BUFFER_FLAGS_DEFAULT);
+}
+
+static void
+test_buffer_contents (fixture_t *fixture, gconstpointer user_data)
+{
+  hb_buffer_t *b = fixture->buffer;
+  unsigned int i, len, len2;
+  buffer_type_t buffer_type = GPOINTER_TO_INT (user_data);
+  hb_glyph_info_t *glyphs;
+
+  if (buffer_type == BUFFER_EMPTY) {
+    g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+    return;
+  }
+
+  len = hb_buffer_get_population (b);
+  hb_buffer_get_glyph_infos (b, NULL); /* test NULL */
+  glyphs = hb_buffer_get_glyph_infos (b, &len2);
+  g_assert_cmpint (len, ==, len2);
+  g_assert_cmpint (len, ==, 5);
+
+  for (i = 0; i < len; i++) {
+    g_assert_cmphex (glyphs[i].mask,      ==, 1);
+    g_assert_cmphex (glyphs[i].var1.u32,  ==, 0);
+    g_assert_cmphex (glyphs[i].var2.u32,  ==, 0);
+  }
+
+  for (i = 0; i < len; i++) {
+    unsigned int cluster;
+    cluster = 1+i;
+    if (i >= 2) {
+      if (buffer_type == BUFFER_UTF16)
+	cluster++;
+      else if (buffer_type == BUFFER_UTF8)
+        cluster += 3;
+    }
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+    g_assert_cmphex (glyphs[i].cluster,   ==, cluster);
+  }
+
+  /* reverse, test, and reverse back */
+
+  hb_buffer_reverse (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[len-i]);
+
+  hb_buffer_reverse (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+
+  /* reverse_clusters works same as reverse for now since each codepoint is
+   * in its own cluster */
+
+  hb_buffer_reverse_clusters (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[len-i]);
+
+  hb_buffer_reverse_clusters (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+
+  /* now form a cluster and test again */
+  glyphs[2].cluster = glyphs[1].cluster;
+
+  /* reverse, test, and reverse back */
+
+  hb_buffer_reverse (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[len-i]);
+
+  hb_buffer_reverse (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+
+  /* reverse_clusters twice still should return the original string,
+   * but when applied once, the 1-2 cluster should be retained. */
+
+  hb_buffer_reverse_clusters (b);
+  for (i = 0; i < len; i++) {
+    unsigned int j = len-1-i;
+    if (j == 1)
+      j = 2;
+    else if (j == 2)
+      j = 1;
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+j]);
+  }
+
+  hb_buffer_reverse_clusters (b);
+  for (i = 0; i < len; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+
+
+  /* test setting length */
+
+  /* enlarge */
+  g_assert (hb_buffer_set_length (b, 10));
+  glyphs = hb_buffer_get_glyph_infos (b, NULL);
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 10);
+  for (i = 0; i < 5; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+  for (i = 5; i < 10; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, 0);
+  /* shrink */
+  g_assert (hb_buffer_set_length (b, 3));
+  glyphs = hb_buffer_get_glyph_infos (b, NULL);
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 3);
+  for (i = 0; i < 3; i++)
+    g_assert_cmphex (glyphs[i].codepoint, ==, utf32[1+i]);
+
+
+  g_assert (hb_buffer_allocation_successful (b));
+
+
+  /* test reset clears content */
+
+  hb_buffer_reset (b);
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+}
+
+static void
+test_buffer_allocation (fixture_t *fixture, gconstpointer user_data)
+{
+  hb_buffer_t *b = fixture->buffer;
+
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+
+  g_assert (hb_buffer_pre_allocate (b, 100));
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+  g_assert (hb_buffer_allocation_successful (b));
+
+  /* lets try a huge allocation, make sure it fails */
+  g_assert (!hb_buffer_pre_allocate (b, (unsigned int) -1));
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+  g_assert (!hb_buffer_allocation_successful (b));
+
+  /* small one again */
+  g_assert (hb_buffer_pre_allocate (b, 50));
+  g_assert_cmpint (hb_buffer_get_population (b), ==, 0);
+  g_assert (!hb_buffer_allocation_successful (b));
+
+  hb_buffer_reset (b);
+  g_assert (hb_buffer_allocation_successful (b));
+
+  /* all allocation and size  */
+  g_assert (!hb_buffer_pre_allocate (b, ((unsigned int) -1) / 20 + 1));
+  g_assert (!hb_buffer_allocation_successful (b));
+
+  hb_buffer_reset (b);
+  g_assert (hb_buffer_allocation_successful (b));
+
+  /* technically, this one can actually pass on 64bit machines, but
+   * I'm doubtful that any malloc allows 4GB allocations at a time.
+   * But let's only enable it on a 32-bit machine. */
+  if (sizeof (long) == 4) {
+    g_assert (!hb_buffer_pre_allocate (b, ((unsigned int) -1) / 20 - 1));
+    g_assert (!hb_buffer_allocation_successful (b));
+  }
+
+  hb_buffer_reset (b);
+  g_assert (hb_buffer_allocation_successful (b));
+}
+#endif
+
+static void
+test_empty (hb_set_t *b)
+{
+  g_assert_cmpint (hb_set_get_population (b), ==, 0);
+  g_assert_cmpint (hb_set_get_min (b), ==, (hb_codepoint_t) -1);
+  g_assert_cmpint (hb_set_get_max (b), ==, (hb_codepoint_t) -1);
+}
+
+static void
+test_set_empty (void)
+{
+  hb_set_t *b = hb_set_get_empty ();
+
+  g_assert (hb_set_get_empty ());
+  g_assert (hb_set_get_empty () == b);
+
+  g_assert (!hb_set_allocation_successful (b));
+
+  test_empty (b);
+
+  hb_set_add (b, 13);
+
+  test_empty (b);
+
+  hb_set_invert (b);
+
+  test_empty (b);
+
+  g_assert (!hb_set_allocation_successful (b));
+
+  hb_set_clear (b);
+
+  test_empty (b);
+
+  g_assert (!hb_set_allocation_successful (b));
+}
+
+int
+main (int argc, char **argv)
+{
+  hb_test_init (&argc, &argv);
+
+#if 0
+  hb_test_add (test_set_algebra);
+  hb_test_add (test_set_iter);
+#endif
+  hb_test_add (test_set_empty);
+
+  return hb_test_run();
+}