diff --git a/test/Makefile.am b/test/Makefile.am
index b726e53..78636fc 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -25,7 +25,7 @@
 					$(PHOSPHOR_LOGGING_CFLAGS) \
 					$(PHOSPHOR_DBUS_INTERFACES_CFLAGS)
 
-generic_ld_flags =  -lgtest_main -lgtest -lstdc++fs \
+generic_ld_flags =  -lgtest_main -lgtest -lgmock -lstdc++fs \
 					$(OESDK_TESTCASE_FLAGS) \
 					$(SYSTEMD_LIBS) \
 					$(SDBUSPLUS_LIBS) \
diff --git a/test/mock_network_manager.hpp b/test/mock_network_manager.hpp
new file mode 100644
index 0000000..a71301e
--- /dev/null
+++ b/test/mock_network_manager.hpp
@@ -0,0 +1,28 @@
+#include "config.h"
+
+#include "network_manager.hpp"
+
+#include <gmock/gmock.h>
+
+namespace phosphor
+{
+namespace network
+{
+
+class MockManager : public phosphor::network::Manager
+{
+  public:
+    MockManager(sdbusplus::bus::bus& bus, const char* path,
+                const std::string& dir) :
+        phosphor::network::Manager(bus, path, dir)
+    {
+    }
+
+    MOCK_METHOD1(restartSystemdUnit, void(const std::string& service));
+
+    friend class TestNetworkManager;
+    friend class TestRtNetlink;
+};
+
+} // namespace network
+} // namespace phosphor
diff --git a/test/test_ethernet_interface.cpp b/test/test_ethernet_interface.cpp
index 1b284a2..9e611a6 100644
--- a/test/test_ethernet_interface.cpp
+++ b/test/test_ethernet_interface.cpp
@@ -1,7 +1,7 @@
 #include "config_parser.hpp"
 #include "ipaddress.hpp"
+#include "mock_network_manager.hpp"
 #include "mock_syscall.hpp"
-#include "network_manager.hpp"
 
 #include <arpa/inet.h>
 #include <net/if.h>
@@ -23,7 +23,7 @@
 {
   public:
     sdbusplus::bus::bus bus;
-    Manager manager;
+    MockManager manager;
     EthernetInterface interface;
     std::string confDir;
     TestEthernetInterface() :
@@ -188,6 +188,7 @@
 TEST_F(TestEthernetInterface, addNTPServers)
 {
     ServerList servers = {"10.1.1.1", "10.2.2.2", "10.3.3.3"};
+    EXPECT_CALL(manager, restartSystemdUnit(networkdService)).Times(1);
     interface.nTPServers(servers);
     fs::path filePath = confDir;
     filePath /= "00-bmc-test0.network";
diff --git a/test/test_network_manager.cpp b/test/test_network_manager.cpp
index d97b182..911a1bd 100644
--- a/test/test_network_manager.cpp
+++ b/test/test_network_manager.cpp
@@ -1,5 +1,5 @@
+#include "mock_network_manager.hpp"
 #include "mock_syscall.hpp"
-#include "network_manager.hpp"
 #include "xyz/openbmc_project/Common/error.hpp"
 
 #include <arpa/inet.h>
@@ -9,7 +9,6 @@
 
 #include <exception>
 #include <experimental/filesystem>
-#include <phosphor-logging/elog-errors.hpp>
 #include <sdbusplus/bus.hpp>
 
 #include <gtest/gtest.h>
@@ -19,13 +18,16 @@
 namespace network
 {
 
+std::unique_ptr<Timer> refreshObjectTimer = nullptr;
+std::unique_ptr<Timer> restartTimer = nullptr;
+
 namespace fs = std::experimental::filesystem;
 
 class TestNetworkManager : public testing::Test
 {
   public:
     sdbusplus::bus::bus bus;
-    Manager manager;
+    MockManager manager;
     std::string confDir;
     TestNetworkManager() :
         bus(sdbusplus::bus::new_default()),
diff --git a/test/test_rtnetlink.cpp b/test/test_rtnetlink.cpp
index ee43bf4..9284600 100644
--- a/test/test_rtnetlink.cpp
+++ b/test/test_rtnetlink.cpp
@@ -1,5 +1,5 @@
+#include "mock_network_manager.hpp"
 #include "mock_syscall.hpp"
-#include "network_manager.hpp"
 #include "rtnetlink_server.hpp"
 #include "types.hpp"
 
@@ -19,9 +19,9 @@
 namespace network
 {
 sdbusplus::bus::bus bus(sdbusplus::bus::new_default());
-std::unique_ptr<Manager> manager = nullptr;
-std::unique_ptr<Timer> refreshObjectTimer = nullptr;
-std::unique_ptr<Timer> restartTimer = nullptr;
+std::unique_ptr<MockManager> manager = nullptr;
+extern std::unique_ptr<Timer> refreshObjectTimer;
+extern std::unique_ptr<Timer> restartTimer;
 EventPtr eventPtr = nullptr;
 
 /** @brief refresh the network objects. */
@@ -50,7 +50,7 @@
     TestRtNetlink()
     {
         manager =
-            std::make_unique<Manager>(bus, "/xyz/openbmc_test/bcd", "/tmp");
+            std::make_unique<MockManager>(bus, "/xyz/openbmc_test/bcd", "/tmp");
         sd_event* events;
         sd_event_default(&events);
         eventPtr.reset(events);
diff --git a/test/test_util.cpp b/test/test_util.cpp
index 437b3cf..6c647ed 100644
--- a/test/test_util.cpp
+++ b/test/test_util.cpp
@@ -2,6 +2,8 @@
 
 #include <netinet/in.h>
 
+#include <xyz/openbmc_project/Common/error.hpp>
+
 #include <gtest/gtest.h>
 
 namespace phosphor
@@ -9,6 +11,8 @@
 namespace network
 {
 
+using InternalFailure =
+    sdbusplus::xyz::openbmc_project::Common::Error::InternalFailure;
 class TestUtil : public testing::Test
 {
   public:
@@ -184,11 +188,10 @@
     address = getNetworkID(AF_INET6, "2001:db8:abcd:dd12::0", 64);
     EXPECT_EQ("2001:db8:abcd:dd12::", address);
 
-    address = getNetworkID(AF_INET, "a.b.c.d", 25);
-    EXPECT_EQ("", address);
+    EXPECT_THROW(getNetworkID(AF_INET, "a.b.c.d", 25), InternalFailure);
 
-    address = getNetworkID(AF_INET6, "2001:db8:gghh:dd12::0", 64);
-    EXPECT_EQ("", address);
+    EXPECT_THROW(getNetworkID(AF_INET6, "2001:db8:gghh:dd12::0", 64),
+                 InternalFailure);
 
     address = getNetworkID(AF_INET6, "fe80::201:6cff:fe80:228", 64);
     EXPECT_EQ("fe80::", address);
diff --git a/test/test_vlan_interface.cpp b/test/test_vlan_interface.cpp
index 1bcd87a..7179212 100644
--- a/test/test_vlan_interface.cpp
+++ b/test/test_vlan_interface.cpp
@@ -1,7 +1,7 @@
 #include "config_parser.hpp"
 #include "ipaddress.hpp"
+#include "mock_network_manager.hpp"
 #include "mock_syscall.hpp"
-#include "network_manager.hpp"
 #include "vlan_interface.hpp"
 
 #include <arpa/inet.h>
@@ -25,7 +25,7 @@
 {
   public:
     sdbusplus::bus::bus bus;
-    Manager manager;
+    MockManager manager;
     EthernetInterface interface;
     std::string confDir;
     TestVlanInterface() :