diff --git a/starboard/nplb/BUILD.gn b/starboard/nplb/BUILD.gn
index 0fc5c6ab3081..9e42544a8a68 100644
--- a/starboard/nplb/BUILD.gn
+++ b/starboard/nplb/BUILD.gn
@@ -137,6 +137,8 @@ target(gtest_target_type, "nplb") {
     "player_write_sample_test.cc",
     "posix_compliance/posix_string_compare_no_case_n_test.cc",
     "posix_compliance/posix_string_compare_no_case_test.cc",
+    "posix_compliance/posix_string_format_test.cc",
+    "posix_compliance/posix_string_format_wide_test.cc",
     "random_helpers.cc",
     "recursive_mutex_test.cc",
     "rwlock_test.cc",
diff --git a/starboard/nplb/posix_compliance/posix_string_compare_no_case_n_test.cc b/starboard/nplb/posix_compliance/posix_string_compare_no_case_n_test.cc
index 843b5800f45e..6b98cb4c6c40 100644
--- a/starboard/nplb/posix_compliance/posix_string_compare_no_case_n_test.cc
+++ b/starboard/nplb/posix_compliance/posix_string_compare_no_case_n_test.cc
@@ -17,7 +17,6 @@
 
 namespace starboard {
 namespace nplb {
-namespace posix_compliance {
 namespace {
 
 #if SB_API_VERSION >= 16
@@ -58,6 +57,5 @@ TEST(PosixCompareNoCaseNTest, SunnyDayCase) {
 #endif  // SB_API_VERSION >= 16
 
 }  // namespace
-}  // namespace posix_compliance
 }  // namespace nplb
 }  // namespace starboard
diff --git a/starboard/nplb/posix_compliance/posix_string_compare_no_case_test.cc b/starboard/nplb/posix_compliance/posix_string_compare_no_case_test.cc
index 8de3563b7548..1417a10bf693 100644
--- a/starboard/nplb/posix_compliance/posix_string_compare_no_case_test.cc
+++ b/starboard/nplb/posix_compliance/posix_string_compare_no_case_test.cc
@@ -17,7 +17,6 @@
 
 namespace starboard {
 namespace nplb {
-namespace posix_compliance {
 namespace {
 
 #if SB_API_VERSION >= 16
@@ -40,6 +39,5 @@ TEST(PosixCompareNoCaseTest, SunnyDayCase) {
 }
 #endif  // SB_API_VERSION >= 16
 }  // namespace
-}  // namespace posix_compliance
 }  // namespace nplb
 }  // namespace starboard
diff --git a/starboard/nplb/posix_compliance/posix_string_format_test.cc b/starboard/nplb/posix_compliance/posix_string_format_test.cc
new file mode 100644
index 000000000000..e1a793dc15c9
--- /dev/null
+++ b/starboard/nplb/posix_compliance/posix_string_format_test.cc
@@ -0,0 +1,50 @@
+// Copyright 2015 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Here we are not trying to do anything fancy, just to really sanity check that
+// this is hooked up to something.
+#if SB_API_VERSION >= 16
+
+#include "starboard/common/string.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace starboard {
+namespace nplb {
+namespace {
+
+int Format(char* out_buffer, size_t buffer_size, const char* format, ...) {
+  va_list arguments;
+  va_start(arguments, format);
+  int result = vsnprintf(out_buffer, buffer_size, format, arguments);
+  va_end(arguments);
+  return result;
+}
+
+TEST(PosixFormatTest, SunnyDay) {
+  const char kExpected[] = "a1b2c3test";
+  char destination[1024] = {0};
+  int result = Format(destination, SB_ARRAY_SIZE(destination), "a%db%dc%d%s", 1,
+                      2, 3, "test");
+  size_t expected_length = strlen(kExpected);
+  EXPECT_EQ(expected_length, result);
+  for (size_t i = 0; i <= expected_length; ++i) {
+    EXPECT_EQ(kExpected[i], destination[i]);
+  }
+}
+
+}  // namespace
+}  // namespace nplb
+}  // namespace starboard
+   //
+#endif  // SB_API_VERSION >= 16
diff --git a/starboard/nplb/posix_compliance/posix_string_format_wide_test.cc b/starboard/nplb/posix_compliance/posix_string_format_wide_test.cc
new file mode 100644
index 000000000000..1a6e39defc38
--- /dev/null
+++ b/starboard/nplb/posix_compliance/posix_string_format_wide_test.cc
@@ -0,0 +1,53 @@
+// Copyright 2015 The Cobalt Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// Here we are not trying to do anything fancy, just to really sanity check that
+// this is hooked up to something.
+#if SB_API_VERSION >= 16
+
+#include "starboard/common/string.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace starboard {
+namespace nplb {
+namespace {
+
+int Format(wchar_t* out_buffer,
+           size_t buffer_size,
+           const wchar_t* format,
+           ...) {
+  va_list arguments;
+  va_start(arguments, format);
+  int result = vswprintf(out_buffer, buffer_size, format, arguments);
+  va_end(arguments);
+  return result;
+}
+
+TEST(PosixFormatWideTest, SunnyDay) {
+  const wchar_t kExpected[] = L"a1b2c3test";
+  wchar_t destination[1024] = {0};
+  int result = Format(destination, SB_ARRAY_SIZE(destination), L"a%db%dc%d%s",
+                      1, 2, 3, "test");
+  size_t expected_length = wcslen(kExpected);
+  EXPECT_EQ(expected_length, result);
+  for (size_t i = 0; i <= expected_length; ++i) {
+    EXPECT_EQ(kExpected[i], destination[i]);
+  }
+}
+
+}  // namespace
+}  // namespace nplb
+}  // namespace starboard
+
+#endif  // SB_API_VERSION >= 16