diff --git a/test/api/Makefile.am b/test/api/Makefile.am
index bf29d2200..88502ac5c 100644
--- a/test/api/Makefile.am
+++ b/test/api/Makefile.am
@@ -42,6 +42,7 @@ TEST_PROGS = \
 	test-object \
 	test-ot-alternates \
 	test-ot-color \
+	test-ot-collect-glyphs \
 	test-ot-face \
 	test-ot-glyphname \
 	test-ot-ligature-carets \
diff --git a/test/api/meson.build b/test/api/meson.build
index 5c8b6022f..a1c862b61 100644
--- a/test/api/meson.build
+++ b/test/api/meson.build
@@ -17,6 +17,7 @@ tests = [
   'test-map.c',
   'test-object.c',
   'test-ot-alternates.c',
+  'test-ot-collect-glyphs.c',
   'test-ot-color.c',
   'test-ot-face.c',
   'test-ot-glyphname.c',
diff --git a/test/api/test-ot-collect-glyphs.c b/test/api/test-ot-collect-glyphs.c
new file mode 100644
index 000000000..9afb1ad4b
--- /dev/null
+++ b/test/api/test-ot-collect-glyphs.c
@@ -0,0 +1,209 @@
+/*
+ * Copyright © 2021  Khaled Hosny
+ *
+ *  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.
+ */
+
+#include "hb-test.h"
+
+#include <hb.h>
+#include <hb-ot.h>
+
+#define BEGIN(tag, idx) \
+  hb_ot_layout_lookup_collect_glyphs (face, tag, idx, before, input, after, output) \
+
+#define END() \
+  hb_set_clear (before); \
+  hb_set_clear (input); \
+  hb_set_clear (after); \
+  hb_set_clear (output)
+
+static void
+test_ot_layout_lookup_collect_glyphs_source_sans (void)
+{
+  hb_face_t *face = hb_test_open_font_file ("fonts/SourceSansPro-Regular.otf");
+
+  hb_set_t *before = hb_set_create();
+  hb_set_t *input = hb_set_create();
+  hb_set_t *after = hb_set_create();
+  hb_set_t *output = hb_set_create();
+  hb_codepoint_t g = HB_SET_VALUE_INVALID;
+
+  /* SingleSubst */
+  BEGIN(HB_OT_TAG_GSUB, 0);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+  g_assert_cmpuint (684, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (54, ==, g);
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+  g_assert_cmpuint (372, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (574, ==, g);
+  END();
+
+  /* AlternateSubst */
+  BEGIN(HB_OT_TAG_GSUB, 1);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (143, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (2, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+
+  g_assert_cmpuint (319, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (519, ==, g);
+  END();
+
+  /* MultipleSubst */
+  BEGIN(HB_OT_TAG_GSUB, 7);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (10, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (92, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+
+  g_assert_cmpuint (9, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (6, ==, g);
+  END();
+
+  /* LigatureSubst */
+  BEGIN(HB_OT_TAG_GSUB, 10);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (14, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (1823, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+
+  g_assert_cmpuint (22, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (1897, ==, g);
+  END();
+
+  /* ChainContextSubstFormat3 */
+  BEGIN(HB_OT_TAG_GSUB, 8);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (10, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (92, ==, g);
+
+  g_assert_cmpuint (2, ==, hb_set_get_population (after));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (after, &g));
+  g_assert_cmpuint (1826, ==, g);
+  g_assert (hb_set_next (after, &g));
+  g_assert_cmpuint (1837, ==, g);
+
+  g_assert_cmpuint (9, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (6, ==, g);
+  END();
+
+  /* ChainContextSubstFormat3 */
+  BEGIN(HB_OT_TAG_GSUB, 13);
+  g_assert_cmpuint (771, ==, hb_set_get_population (before));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (before, &g));
+  g_assert_cmpuint (2, ==, g);
+
+  g_assert_cmpuint (28, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (1823, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+
+  g_assert_cmpuint (48, ==, hb_set_get_population (output));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (output, &g));
+  g_assert_cmpuint (325, ==, g);
+  END();
+
+  /* MarkBasePos */
+  BEGIN(HB_OT_TAG_GPOS, 0);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (179, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (28, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+  g_assert_cmpuint (0, ==, hb_set_get_population (output));
+  END();
+
+  /* MarkMarkPos */
+  BEGIN(HB_OT_TAG_GPOS, 9);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (48, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (1823, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+  g_assert_cmpuint (0, ==, hb_set_get_population (output));
+  END();
+
+  /* PairPos */
+  BEGIN(HB_OT_TAG_GPOS, 10);
+  g_assert_cmpuint (0, ==, hb_set_get_population (before));
+
+  g_assert_cmpuint (1426, ==, hb_set_get_population (input));
+  g = HB_SET_VALUE_INVALID;
+  g_assert (hb_set_next (input, &g));
+  g_assert_cmpuint (2, ==, g);
+
+  g_assert_cmpuint (0, ==, hb_set_get_population (after));
+  g_assert_cmpuint (0, ==, hb_set_get_population (output));
+  END();
+
+  hb_face_destroy (face);
+  hb_set_destroy (before);
+  hb_set_destroy (input);
+  hb_set_destroy (after);
+  hb_set_destroy (output);
+}
+
+int
+main (int argc, char **argv)
+{
+  hb_test_init (&argc, &argv);
+  hb_test_add (test_ot_layout_lookup_collect_glyphs_source_sans);
+  return hb_test_run ();
+}