diff --git a/phosphor-regulators/test/actions/i2c_write_byte_action_tests.cpp b/phosphor-regulators/test/actions/i2c_write_byte_action_tests.cpp
new file mode 100644
index 0000000..1a858e3
--- /dev/null
+++ b/phosphor-regulators/test/actions/i2c_write_byte_action_tests.cpp
@@ -0,0 +1,278 @@
+/**
+ * Copyright © 2020 IBM Corporation
+ *
+ * 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.
+ */
+#include "action_environment.hpp"
+#include "action_error.hpp"
+#include "device.hpp"
+#include "i2c_interface.hpp"
+#include "i2c_write_byte_action.hpp"
+#include "id_map.hpp"
+#include "mocked_i2c_interface.hpp"
+
+#include <cstdint>
+#include <memory>
+#include <stdexcept>
+#include <string>
+#include <utility>
+
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+
+using namespace phosphor::power::regulators;
+
+using ::testing::A;
+using ::testing::Return;
+using ::testing::SetArgReferee;
+using ::testing::Throw;
+using ::testing::TypedEq;
+
+TEST(I2CWriteByteActionTests, Constructor)
+{
+    // Test where mask is not specified
+    {
+        I2CWriteByteAction action{0x7C, 0x0A};
+        EXPECT_EQ(action.getRegister(), 0x7C);
+        EXPECT_EQ(action.getValue(), 0x0A);
+        EXPECT_EQ(action.getMask(), 0xFF);
+    }
+
+    // Test where mask is specified
+    {
+        I2CWriteByteAction action{0xA0, 0xD6, 0xC3};
+        EXPECT_EQ(action.getRegister(), 0xA0);
+        EXPECT_EQ(action.getValue(), 0xD6);
+        EXPECT_EQ(action.getMask(), 0xC3);
+    }
+}
+
+TEST(I2CWriteByteActionTests, Execute)
+{
+    // Test where works: Mask not specified
+    try
+    {
+        // Create mock I2CInterface
+        std::unique_ptr<i2c::MockedI2CInterface> i2cInterface =
+            std::make_unique<i2c::MockedI2CInterface>();
+        EXPECT_CALL(*i2cInterface, isOpen).Times(1).WillOnce(Return(true));
+        EXPECT_CALL(*i2cInterface, read(A<uint8_t>(), A<uint8_t&>())).Times(0);
+        EXPECT_CALL(*i2cInterface,
+                    write(TypedEq<uint8_t>(0x7C), TypedEq<uint8_t>(0x0A)))
+            .Times(1);
+
+        // Create Device, IDMap, and ActionEnvironment
+        Device device{"reg1", true, "/system/chassis/motherboard/reg1",
+                      std::move(i2cInterface)};
+        IDMap idMap{};
+        idMap.addDevice(device);
+        ActionEnvironment env{idMap, "reg1"};
+
+        I2CWriteByteAction action{0x7C, 0x0A};
+        EXPECT_EQ(action.execute(env), true);
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+
+    // Test where works: Mask specified
+    try
+    {
+        // Create mock I2CInterface: read() returns value 0x69
+        std::unique_ptr<i2c::MockedI2CInterface> i2cInterface =
+            std::make_unique<i2c::MockedI2CInterface>();
+        EXPECT_CALL(*i2cInterface, isOpen).Times(1).WillOnce(Return(true));
+        EXPECT_CALL(*i2cInterface, read(0xA0, A<uint8_t&>()))
+            .Times(1)
+            .WillOnce(SetArgReferee<1>(0x69));
+        EXPECT_CALL(*i2cInterface,
+                    write(TypedEq<uint8_t>(0xA0), TypedEq<uint8_t>(0xEA)))
+            .Times(1);
+
+        // Create Device, IDMap, and ActionEnvironment
+        Device device{"reg1", true, "/system/chassis/motherboard/reg1",
+                      std::move(i2cInterface)};
+        IDMap idMap{};
+        idMap.addDevice(device);
+        ActionEnvironment env{idMap, "reg1"};
+
+        // Value to write       : 0xD6 = 1101 0110
+        // Mask                 : 0xC3 = 1100 0011
+        // Current value        : 0x69 = 0110 1001
+        // Value to write & mask: 0xC2 = 1100 0010
+        // ~Mask                : 0x3C = 0011 1100
+        // Current value & ~mask: 0x28 = 0010 1000
+        // Final value to write : 0xEA = 1110 1010
+        I2CWriteByteAction action{0xA0, 0xD6, 0xC3};
+        EXPECT_EQ(action.execute(env), true);
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+
+    // Test where fails: Getting I2CInterface fails
+    try
+    {
+        // Create IDMap and ActionEnvironment
+        IDMap idMap{};
+        ActionEnvironment env{idMap, "reg1"};
+
+        I2CWriteByteAction action{0x7C, 0x0A};
+        action.execute(env);
+        ADD_FAILURE() << "Should not have reached this line.";
+    }
+    catch (const std::invalid_argument& e)
+    {
+        EXPECT_STREQ(e.what(), "Unable to find device with ID \"reg1\"");
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+
+    // Test where fails: Reading byte fails
+    try
+    {
+        // Create mock I2CInterface: read() throws an I2CException
+        std::unique_ptr<i2c::MockedI2CInterface> i2cInterface =
+            std::make_unique<i2c::MockedI2CInterface>();
+        EXPECT_CALL(*i2cInterface, isOpen).Times(1).WillOnce(Return(true));
+        EXPECT_CALL(*i2cInterface, read(0xA0, A<uint8_t&>()))
+            .Times(1)
+            .WillOnce(Throw(
+                i2c::I2CException{"Failed to read byte", "/dev/i2c-1", 0x70}));
+        EXPECT_CALL(*i2cInterface, write(A<uint8_t>(), A<uint8_t>())).Times(0);
+
+        // Create Device, IDMap, and ActionEnvironment
+        Device device{"reg1", true, "/system/chassis/motherboard/reg1",
+                      std::move(i2cInterface)};
+        IDMap idMap{};
+        idMap.addDevice(device);
+        ActionEnvironment env{idMap, "reg1"};
+
+        I2CWriteByteAction action{0xA0, 0xD6, 0xC3};
+        action.execute(env);
+        ADD_FAILURE() << "Should not have reached this line.";
+    }
+    catch (const ActionError& e)
+    {
+        EXPECT_STREQ(e.what(), "ActionError: i2c_write_byte: { register: "
+                               "0xA0, value: 0xD6, mask: 0xC3 }");
+        try
+        {
+            // Re-throw inner I2CException
+            std::rethrow_if_nested(e);
+            ADD_FAILURE() << "Should not have reached this line.";
+        }
+        catch (const i2c::I2CException& ie)
+        {
+            EXPECT_STREQ(
+                ie.what(),
+                "I2CException: Failed to read byte: bus /dev/i2c-1, addr 0x70");
+        }
+        catch (...)
+        {
+            ADD_FAILURE() << "Should not have caught exception.";
+        }
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+
+    // Test where fails: Writing byte fails
+    try
+    {
+        // Create mock I2CInterface: write() throws an I2CException
+        std::unique_ptr<i2c::MockedI2CInterface> i2cInterface =
+            std::make_unique<i2c::MockedI2CInterface>();
+        EXPECT_CALL(*i2cInterface, isOpen).Times(1).WillOnce(Return(true));
+        EXPECT_CALL(*i2cInterface, read(A<uint8_t>(), A<uint8_t&>())).Times(0);
+        EXPECT_CALL(*i2cInterface,
+                    write(TypedEq<uint8_t>(0x7C), TypedEq<uint8_t>(0x1A)))
+            .Times(1)
+            .WillOnce(Throw(
+                i2c::I2CException{"Failed to write byte", "/dev/i2c-1", 0x70}));
+
+        // Create Device, IDMap, and ActionEnvironment
+        Device device{"reg1", true, "/system/chassis/motherboard/reg1",
+                      std::move(i2cInterface)};
+        IDMap idMap{};
+        idMap.addDevice(device);
+        ActionEnvironment env{idMap, "reg1"};
+
+        I2CWriteByteAction action{0x7C, 0x1A};
+        action.execute(env);
+        ADD_FAILURE() << "Should not have reached this line.";
+    }
+    catch (const ActionError& e)
+    {
+        EXPECT_STREQ(e.what(), "ActionError: i2c_write_byte: { register: "
+                               "0x7C, value: 0x1A, mask: 0xFF }");
+        try
+        {
+            // Re-throw inner I2CException
+            std::rethrow_if_nested(e);
+            ADD_FAILURE() << "Should not have reached this line.";
+        }
+        catch (const i2c::I2CException& ie)
+        {
+            EXPECT_STREQ(ie.what(), "I2CException: Failed to write byte: bus "
+                                    "/dev/i2c-1, addr 0x70");
+        }
+        catch (...)
+        {
+            ADD_FAILURE() << "Should not have caught exception.";
+        }
+    }
+    catch (...)
+    {
+        ADD_FAILURE() << "Should not have caught exception.";
+    }
+}
+
+TEST(I2CWriteByteActionTests, GetRegister)
+{
+    I2CWriteByteAction action{0x7C, 0xDE};
+    EXPECT_EQ(action.getRegister(), 0x7C);
+}
+
+TEST(I2CWriteByteActionTests, GetValue)
+{
+    I2CWriteByteAction action{0xA0, 0x03, 0x47};
+    EXPECT_EQ(action.getValue(), 0x03);
+}
+
+TEST(I2CWriteByteActionTests, GetMask)
+{
+    // Test where mask is not specified
+    {
+        I2CWriteByteAction action{0x7C, 0xDE};
+        EXPECT_EQ(action.getMask(), 0xFF);
+    }
+
+    // Test where mask is specified
+    {
+        I2CWriteByteAction action{0xA0, 0x03, 0x47};
+        EXPECT_EQ(action.getMask(), 0x47);
+    }
+}
+
+TEST(I2CWriteByteActionTests, ToString)
+{
+    I2CWriteByteAction action{0x7C, 0xDE, 0xFB};
+    EXPECT_EQ(action.toString(),
+              "i2c_write_byte: { register: 0x7C, value: 0xDE, mask: 0xFB }");
+}