diff --git a/BUILD.gn b/BUILD.gn
index e66517e..f2fe2e1 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -1955,6 +1955,7 @@
       "core/fxcrt/xml/cfx_saxreader_unittest.cpp",
       "core/fxcrt/xml/cfx_xmlsyntaxparser_unittest.cpp",
       "fxbarcode/oned/BC_OnedCode128Writer_unittest.cpp",
+      "fxbarcode/oned/BC_OnedCode39Writer_unittest.cpp",
       "fxbarcode/oned/BC_OnedEAN13Writer_unittest.cpp",
       "fxbarcode/oned/BC_OnedEAN8Writer_unittest.cpp",
       "fxbarcode/pdf417/BC_PDF417HighLevelEncoder_unittest.cpp",
diff --git a/fxbarcode/oned/BC_OnedCode39Writer_unittest.cpp b/fxbarcode/oned/BC_OnedCode39Writer_unittest.cpp
new file mode 100644
index 0000000..27a0410
--- /dev/null
+++ b/fxbarcode/oned/BC_OnedCode39Writer_unittest.cpp
@@ -0,0 +1,184 @@
+// Copyright 2017 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include <cstring>
+
+#include "fxbarcode/oned/BC_OnedCode39Writer.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace {
+
+// 3 wide and 6 narrow modules per char. 1 space between chars.
+const int MODULES_PER_CHAR = 3 * 3 + 6 * 1 + 1;
+
+// '*' is added as the first and last char.
+const int DELIMITER_CHARS = 2;
+
+// Last char may serve as checksum.
+const int CHECKSUM_CHARS = 1;
+
+TEST(OnedCode39WriterTest, SetWideNarrowRatio) {
+  // Code 39 barcodes encode strings of any size into modules in a
+  // unidimensional disposition.
+  // Each module is either: a narrow bar, a narrow space, a wide
+  // bar, or a wide space. Accepted wide-to-narrow ratios are between 2 and 3.
+  // This writer in particular only takes integer ratios, so it's either 2 or 3.
+  CBC_OnedCode39Writer writer;
+  EXPECT_FALSE(writer.SetWideNarrowRatio(0));
+  EXPECT_FALSE(writer.SetWideNarrowRatio(1));
+  EXPECT_TRUE(writer.SetWideNarrowRatio(2));
+  EXPECT_TRUE(writer.SetWideNarrowRatio(3));
+  EXPECT_FALSE(writer.SetWideNarrowRatio(4));
+  EXPECT_FALSE(writer.SetWideNarrowRatio(100));
+
+  writer.SetWideNarrowRatio(3);
+
+  int32_t width;
+  int32_t height;
+  uint8_t* encoded;
+  const char* expected;
+
+  encoded = writer.Encode("PDFIUM", BCFORMAT_CODE_39, width, height);
+  expected =
+      "#   # ### ### # "  // * Start
+      "# ### ### #   # "  // P
+      "# # ###   # ### "  // D
+      "# ### ###   # # "  // F
+      "# ### #   ### # "  // I
+      "###   # # # ### "  // U
+      "### ### # #   # "  // M
+      "#   # ### ### #";  // * End
+  FX_Free(encoded);
+
+  writer.SetWideNarrowRatio(2);
+
+  encoded = writer.Encode("PDFIUM", BCFORMAT_CODE_39, width, height);
+  expected =
+      "#  # ## ## # "  // * Start
+      "# ## ## #  # "  // P
+      "# # ##  # ## "  // D
+      "# ## ##  # # "  // F
+      "# ## #  ## # "  // I
+      "##  # # # ## "  // U
+      "## ## # #  # "  // M
+      "#  # ## ## #";  // * End
+  FX_Free(encoded);
+}
+
+TEST(OnedCode39WriterTest, Encode) {
+  CBC_OnedCode39Writer writer;
+  int32_t width;
+  int32_t height;
+  uint8_t* encoded;
+  const char* expected;
+
+  encoded = writer.Encode("", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((0 + DELIMITER_CHARS) * MODULES_PER_CHAR - 1, width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+
+  encoded = writer.Encode("123", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((3 + DELIMITER_CHARS) * MODULES_PER_CHAR - 1, width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "### #   # # ### "  // 1
+      "# ###   # # ### "  // 2
+      "### ###   # # # "  // 3
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+
+  encoded = writer.Encode("PDFIUM", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((6 + DELIMITER_CHARS) * MODULES_PER_CHAR - 1, width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "# ### ### #   # "  // P
+      "# # ###   # ### "  // D
+      "# ### ###   # # "  // F
+      "# ### #   ### # "  // I
+      "###   # # # ### "  // U
+      "### ### # #   # "  // M
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+
+  encoded = writer.Encode("A -$%./+Z", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((9 + DELIMITER_CHARS) * MODULES_PER_CHAR - 1, width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "### # #   # ### "  // A
+      "#   ### # ### # "  // Space
+      "#   # # ### ### "  // -
+      "#   #   #   # # "  // $
+      "# #   #   #   # "  // %
+      "###   # # ### # "  // .
+      "#   #   # #   # "  // /
+      "#   # #   #   # "  // +
+      "#   ### ### # # "  // Z
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+}
+
+TEST(OnedCode39WriterTest, Checksum) {
+  CBC_OnedCode39Writer writer;
+  int32_t width;
+  int32_t height;
+  uint8_t* encoded;
+  const char* expected;
+
+  writer.SetCalcChecksum(true);
+
+  encoded = writer.Encode("123", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((3 + CHECKSUM_CHARS + DELIMITER_CHARS) * MODULES_PER_CHAR - 1,
+            width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "### #   # # ### "  // 1 (1)
+      "# ###   # # ### "  // 2 (2)
+      "### ###   # # # "  // 3 (3)
+      "# ###   ### # # "  // 6 (6 = (1 + 2 + 3) % 43)
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+
+  encoded = writer.Encode("PDFIUM", BCFORMAT_CODE_39, width, height);
+  EXPECT_EQ(1, height);
+  EXPECT_EQ((6 + CHECKSUM_CHARS + DELIMITER_CHARS) * MODULES_PER_CHAR - 1,
+            width);
+  expected =
+      "#   # ### ### # "  // * Start
+      "# ### ### #   # "  // P (25)
+      "# # ###   # ### "  // D (13)
+      "# ### ###   # # "  // F (15)
+      "# ### #   ### # "  // I (18)
+      "###   # # # ### "  // U (30)
+      "### ### # #   # "  // M (22)
+      "###   # # ### # "  // . (37 = (25 + 13 + 15 + 18 + 30 + 22) % 43)
+      "#   # ### ### #";  // * End
+  for (size_t i = 0; i < strlen(expected); i++) {
+    EXPECT_EQ(expected[i] != ' ', !!encoded[i]) << i;
+  }
+  FX_Free(encoded);
+}
+
+}  // namespace