diff --git a/aos/flatbuffer_merge_test.cc b/aos/flatbuffer_merge_test.cc
new file mode 100644
index 0000000..f102db9
--- /dev/null
+++ b/aos/flatbuffer_merge_test.cc
@@ -0,0 +1,310 @@
+#include "aos/flatbuffer_merge.h"
+
+#include "gtest/gtest.h"
+
+#include "aos/json_to_flatbuffer.h"
+#include "aos/json_to_flatbuffer_generated.h"
+#include "flatbuffers/minireflect.h"
+
+namespace aos {
+namespace testing {
+
+class FlatbufferMerge : public ::testing::Test {
+ public:
+  FlatbufferMerge() {}
+
+  void JsonMerge(const ::std::string in1, const ::std::string in2,
+                 const ::std::string out) {
+    printf("Merging: %s\n", in1.c_str());
+    printf("Merging: %s\n", in2.c_str());
+    const ::std::vector<uint8_t> fb1 = JsonToFlatbuffer(
+        static_cast<const char *>(in1.c_str()), ConfigurationTypeTable());
+
+    const ::std::string in1_nested = "{ \"nested_config\": " + in1 + " }";
+    const ::std::vector<uint8_t> fb1_nested = JsonToFlatbuffer(
+        static_cast<const char *>(in1_nested.c_str()),
+        ConfigurationTypeTable());
+
+    const ::std::vector<uint8_t> fb2 = JsonToFlatbuffer(
+        static_cast<const char *>(in2.c_str()), ConfigurationTypeTable());
+
+    const ::std::string in2_nested = "{ \"nested_config\": " + in2 + " }";
+    const ::std::vector<uint8_t> fb2_nested =
+        JsonToFlatbuffer(static_cast<const char *>(in2_nested.c_str()),
+                         ConfigurationTypeTable());
+
+    const ::std::string out_nested = "{ \"nested_config\": " + out + " }";
+
+    const ::std::vector<uint8_t> empty =
+        JsonToFlatbuffer("{ }", ConfigurationTypeTable());
+
+    ASSERT_NE(fb1.size(), 0u);
+    ASSERT_NE(fb2.size(), 0u);
+    ASSERT_NE(fb1_nested.size(), 0u);
+    ASSERT_NE(fb2_nested.size(), 0u);
+
+    // We now want to run 7 tests.
+    //  in1 merged "" -> in1.
+    //  in2 merged "" -> in2.
+    //  "" merged in1 -> in1.
+    //  "" merged in2 -> in2.
+    //  nullptr merged in1 -> in1.
+    //  in1 merged nullptr -> in1.
+    //  in1 merged in2 -> out.
+
+    {
+      // in1 merged with "" => in1.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1.data(), empty.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // in2 merged with "" => in2.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb2.data(), empty.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in2,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // "" merged with in1 => in1.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(empty.data(), fb1.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // "" merged with in2 => in2.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(empty.data(), fb2.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in2,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // nullptr merged with in1 => in1.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(nullptr, fb1.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1, FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // in1 merged with nullptr => in1.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1.data(), nullptr);
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1, FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // in1 merged with in2 => out.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1.data(), fb2.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      const ::std::string merged_output =
+          FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable());
+      EXPECT_EQ(out, merged_output);
+
+      printf("Merged to: %s\n", merged_output.c_str());
+    }
+
+    // Now, to make things extra exciting, nest a config inside a config.  And
+    // run all the tests.  This will exercise some fun nested merges and copies.
+
+    {
+      // in1_nested merged with "" => in1.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1_nested.data(), empty.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // in2_nested merged with "" => in2_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb2_nested.data(), empty.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in2_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // "" merged with in1_nested => in1_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(empty.data(), fb1_nested.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // "" merged with in2_nested => in2_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(empty.data(), fb2_nested.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in2_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // nullptr merged with in1_nested => in1_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(nullptr, fb1_nested.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // nullptr merged with in1_nested => in1_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1_nested.data(), nullptr);
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(in1_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+
+    {
+      // in1_nested merged with in2_nested => out_nested.
+      ::std::vector<uint8_t> fb_merged =
+          MergeFlatBuffers<Configuration>(fb1_nested.data(), fb2_nested.data());
+      ASSERT_NE(fb_merged.size(), 0u);
+
+      EXPECT_EQ(out_nested,
+                FlatbufferToJson(fb_merged.data(), ConfigurationTypeTable()));
+    }
+  }
+};
+
+// Test the easy ones.  Test every type, single, no nesting.
+TEST_F(FlatbufferMerge, Basic) {
+  JsonMerge("{ \"foo_bool\": true }", "{ \"foo_bool\": false }",
+            "{ \"foo_bool\": false }");
+
+  JsonMerge("{ \"foo_bool\": false }", "{ \"foo_bool\": true }",
+            "{ \"foo_bool\": true }");
+
+  JsonMerge("{ \"foo_byte\": 5 }", "{ \"foo_byte\": -7 }",
+            "{ \"foo_byte\": -7 }");
+
+  JsonMerge("{ \"foo_ubyte\": 5 }", "{ \"foo_ubyte\": 7 }",
+            "{ \"foo_ubyte\": 7 }");
+
+  JsonMerge("{ \"foo_short\": 5 }", "{ \"foo_short\": 7 }",
+            "{ \"foo_short\": 7 }");
+
+  JsonMerge("{ \"foo_int\": 5 }", "{ \"foo_int\": 7 }", "{ \"foo_int\": 7 }");
+
+  JsonMerge("{ \"foo_uint\": 5 }", "{ \"foo_uint\": 7 }",
+            "{ \"foo_uint\": 7 }");
+
+  JsonMerge("{ \"foo_long\": 5 }", "{ \"foo_long\": 7 }",
+            "{ \"foo_long\": 7 }");
+
+  JsonMerge("{ \"foo_ulong\": 5 }", "{ \"foo_ulong\": 7 }",
+            "{ \"foo_ulong\": 7 }");
+
+  JsonMerge("{ \"foo_float\": 5.0 }", "{ \"foo_float\": 7.1 }",
+            "{ \"foo_float\": 7.1 }");
+
+  JsonMerge("{ \"foo_double\": 5.0 }", "{ \"foo_double\": 7.1 }",
+            "{ \"foo_double\": 7.1 }");
+}
+
+// Test arrays of simple types.
+TEST_F(FlatbufferMerge, Array) {
+  JsonMerge("{ \"foo_string\": \"baz\" }", "{ \"foo_string\": \"bar\" }",
+            "{ \"foo_string\": \"bar\" }");
+
+  JsonMerge("{ \"vector_foo_bool\": [ true, true, false ] }",
+            "{ \"vector_foo_bool\": [ false, true, true, false ] }",
+            "{ \"vector_foo_bool\": [ true, true, false, false, "
+            "true, true, false ] }");
+
+  JsonMerge("{ \"vector_foo_byte\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_byte\": [ -3, 1, 3, 2 ] }",
+            "{ \"vector_foo_byte\": [ 9, 7, 1, -3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_ubyte\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_ubyte\": [ 3, 1, 3, 2 ] }",
+            "{ \"vector_foo_ubyte\": [ 9, 7, 1, 3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_short\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_short\": [ -3, 1, 3, 2 ] }",
+            "{ \"vector_foo_short\": [ 9, 7, 1, -3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_ushort\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_ushort\": [ 3, 1, 3, 2 ] }",
+            "{ \"vector_foo_ushort\": [ 9, 7, 1, 3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_int\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_int\": [ -3, 1, 3, 2 ] }",
+            "{ \"vector_foo_int\": [ 9, 7, 1, -3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_uint\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_uint\": [ 3, 1, 3, 2 ] }",
+            "{ \"vector_foo_uint\": [ 9, 7, 1, 3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_long\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_long\": [ -3, 1, 3, 2 ] }",
+            "{ \"vector_foo_long\": [ 9, 7, 1, -3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_ulong\": [ 9, 7, 1 ] }",
+            "{ \"vector_foo_ulong\": [ 3, 1, 3, 2 ] }",
+            "{ \"vector_foo_ulong\": [ 9, 7, 1, 3, 1, 3, 2 ] }");
+
+  JsonMerge("{ \"vector_foo_float\": [ 9.0, 7.0, 1.0 ] }",
+            "{ \"vector_foo_float\": [ -3.0, 1.3, 3.0, 2.0 ] }",
+            "{ \"vector_foo_float\": [ 9.0, 7.0, 1.0, -3.0, 1.3, 3.0, 2.0 ] }");
+
+  JsonMerge("{ \"vector_foo_string\": [ \"9\", \"7\", \"1 \" ] }",
+            "{ \"vector_foo_string\": [ \"31\", \"32\" ] }",
+            "{ \"vector_foo_string\": [ \"9\", \"7\", \"1 \", \"31\", \"32\" ] }");
+}
+
+// Test nested messages, and arrays of nested messages.
+TEST_F(FlatbufferMerge, NestedStruct) {
+  JsonMerge(
+      "{ \"single_application\": { \"name\": \"woot\" } }",
+      "{ \"single_application\": { \"name\": \"wow\", \"priority\": 7 } }",
+      "{ \"single_application\": { \"name\": \"wow\", \"priority\": 7 } }");
+
+  JsonMerge(
+      "{ \"single_application\": { \"name\": \"wow\", \"priority\": 7 } }",
+      "{ \"single_application\": { \"name\": \"woot\" } }",
+      "{ \"single_application\": { \"name\": \"woot\", \"priority\": 7 } }");
+
+  JsonMerge("{ \"apps\": [ { \"name\": \"woot\" }, { \"name\": \"wow\" } ] }",
+            "{ \"apps\": [ { \"name\": \"woo2\" }, { \"name\": \"wo3\" } ] }",
+            "{ \"apps\": [ { \"name\": \"woot\" }, { \"name\": \"wow\" }, { "
+            "\"name\": \"woo2\" }, { \"name\": \"wo3\" } ] }");
+}
+
+// TODO(austin): enums
+// TODO(austin): unions
+// TODO(austin): struct
+
+}  // namespace testing
+}  // namespace aos