new file mode 100644
--- /dev/null
+++ b/mfbt/tests/TestSmallPointerArray.cpp
@@ -0,0 +1,196 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/SmallPointerArray.h"
+
+#define PTR1 (void*)0x4
+#define PTR2 (void*)0x5
+#define PTR3 (void*)0x6
+
+// We explicitly test sizes up to 3 here, as that is when SmallPointerArray<>
+// switches to the storage method used for larger arrays.
+void TestArrayManipulation()
+{
+  using namespace mozilla;
+  SmallPointerArray<void> testArray;
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 0);
+  MOZ_RELEASE_ASSERT(sizeof(testArray) == 2 * sizeof(void*));
+
+  testArray.AppendElement(PTR1);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+
+  testArray.AppendElement(PTR2);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 2);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+  MOZ_RELEASE_ASSERT(testArray[1] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(1) == PTR2);
+
+  testArray.RemoveElement(PTR1);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR2);
+
+  testArray.AppendElement(PTR1);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 2);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR2);
+  MOZ_RELEASE_ASSERT(testArray[1] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(1) == PTR1);
+
+  testArray.AppendElement(PTR3);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 3);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR2);
+  MOZ_RELEASE_ASSERT(testArray[1] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(1) == PTR1);
+  MOZ_RELEASE_ASSERT(testArray[2] == PTR3);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(2) == PTR3);
+
+  testArray.RemoveElement(PTR1);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 2);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR2);
+  MOZ_RELEASE_ASSERT(testArray[1] == PTR3);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(1) == PTR3);
+
+  testArray.RemoveElement(PTR2);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR3);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR3);
+
+  testArray.RemoveElement(PTR3);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 0);
+
+  testArray.Clear();
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 0);
+
+  testArray.AppendElement(PTR1);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+
+  testArray.AppendElement(PTR2);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 2);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+  MOZ_RELEASE_ASSERT(testArray[1] == PTR2);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(1) == PTR2);
+
+  testArray.RemoveElement(PTR2);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+
+  testArray.RemoveElement(PTR3);
+
+  MOZ_RELEASE_ASSERT(testArray.Length() == 1);
+  MOZ_RELEASE_ASSERT(testArray[0] == PTR1);
+  MOZ_RELEASE_ASSERT(testArray.ElementAt(0) == PTR1);
+}
+
+void TestRangeBasedLoops()
+{
+  using namespace mozilla;
+  SmallPointerArray<void> testArray;
+  void* verification[3];
+  uint32_t entries = 0;
+
+  for (void* test : testArray) {
+    entries++;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 0);
+
+  testArray.AppendElement(PTR1);
+
+  for (void* test : testArray) {
+    verification[entries++] = test;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 1);
+  MOZ_RELEASE_ASSERT(verification[0] == PTR1);
+
+  entries = 0;
+
+  testArray.AppendElement(PTR2);
+
+  for (void* test : testArray) {
+    verification[entries++] = test;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 2);
+  MOZ_RELEASE_ASSERT(verification[0] == PTR1);
+  MOZ_RELEASE_ASSERT(verification[1] == PTR2);
+
+  entries = 0;
+
+  testArray.RemoveElement(PTR1);
+
+  for (void* test : testArray) {
+    verification[entries++] = test;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 1);
+  MOZ_RELEASE_ASSERT(verification[0] == PTR2);
+
+  entries = 0;
+
+  testArray.AppendElement(PTR1);
+  testArray.AppendElement(PTR3);
+
+  for (void* test : testArray) {
+    verification[entries++] = test;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 3);
+  MOZ_RELEASE_ASSERT(verification[0] == PTR2);
+  MOZ_RELEASE_ASSERT(verification[1] == PTR1);
+  MOZ_RELEASE_ASSERT(verification[2] == PTR3);
+
+  entries = 0;
+
+  testArray.RemoveElement(PTR1);
+  testArray.RemoveElement(PTR2);
+  testArray.RemoveElement(PTR3);
+
+  for (void* test : testArray) {
+    entries++;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 0);
+
+  testArray.Clear();
+
+  for (void* test : testArray) {
+    entries++;
+  }
+
+  MOZ_RELEASE_ASSERT(entries == 0);
+}
+
+int
+main()
+{
+  TestArrayManipulation();
+  TestRangeBasedLoops();
+  return 0;
+}

--- a/mfbt/tests/moz.build
+++ b/mfbt/tests/moz.build
@@ -41,16 +41,17 @@ CppUnitTests([
     'TestRange',
     'TestRefPtr',
     'TestResult',
     'TestRollingMean',
     'TestSaturate',
     'TestScopeExit',
     'TestSegmentedVector',
     'TestSHA1',
+    'TestSmallPointerArray',
     'TestSplayTree',
     'TestTemplateLib',
     'TestTuple',
     'TestTypedEnum',
     'TestTypeTraits',
     'TestUniquePtr',
     'TestVariant',
     'TestVector',