diff --git a/.travis.yml b/.travis.yml
index 099073b46..099782b16 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -7,9 +7,10 @@ matrix:
         sources:
         - ubuntu-toolchain-r-test
         packages:
-        - g++
+        - g++-9
+        - gcc-9
     env:
-    - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7"
+    - MATRIX_EVAL="CC=gcc-9 && CXX=g++-9"
     before_install:
     - eval "${MATRIX_EVAL}"
     - pip install gcovr
diff --git a/src/ayab/global_hw_test.cpp b/src/ayab/global_hw_test.cpp
new file mode 100644
index 000000000..dfdc6be90
--- /dev/null
+++ b/src/ayab/global_hw_test.cpp
@@ -0,0 +1,87 @@
+/*!
+ * \file global_hw_test.cpp
+ * This file is part of AYAB.
+ *
+ *    AYAB is free software: you can redistribute it and/or modify
+ *    it under the terms of the GNU General Public License as published by
+ *    the Free Software Foundation, either version 3 of the License, or
+ *    (at your option) any later version.
+ *
+ *    AYAB is distributed in the hope that it will be useful,
+ *    but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *    GNU General Public License for more details.
+ *
+ *    You should have received a copy of the GNU General Public License
+ *    along with AYAB.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ *    Original Work Copyright 2013 Christian Obersteiner, Andreas Müller
+ *    Modified Work Copyright 2020 Sturla Lange, Tom Price
+ *    http://ayab-knitting.com
+ */
+
+#include "hw_test.h"
+
+// static member functions
+
+void GlobalHardwareTest::helpCmd() {
+  m_instance->helpCmd();
+}
+
+void GlobalHardwareTest::sendCmd() {
+  m_instance->sendCmd();
+}
+
+void GlobalHardwareTest::beepCmd() {
+  m_instance->beepCmd();
+}
+
+void GlobalHardwareTest::setSingleCmd() {
+  m_instance->setSingleCmd();
+}
+
+void GlobalHardwareTest::setAllCmd() {
+  m_instance->setAllCmd();
+}
+
+void GlobalHardwareTest::readEOLsensorsCmd() {
+  m_instance->readEOLsensorsCmd();
+}
+
+void GlobalHardwareTest::readEncodersCmd() {
+  m_instance->readEncodersCmd();
+}
+
+void GlobalHardwareTest::autoReadCmd() {
+  m_instance->autoReadCmd();
+}
+
+void GlobalHardwareTest::autoTestCmd() {
+  m_instance->autoTestCmd();
+}
+
+void GlobalHardwareTest::stopCmd() {
+  m_instance->stopCmd();
+}
+
+void GlobalHardwareTest::quitCmd() {
+  m_instance->quitCmd();
+}
+
+void GlobalHardwareTest::unrecognizedCmd(const char *buffer) {
+  m_instance->unrecognizedCmd(buffer);
+}
+
+void GlobalHardwareTest::setUp() {
+  m_instance->setUp();
+}
+
+void GlobalHardwareTest::loop() {
+  m_instance->loop();
+}
+
+#ifndef AYAB_TESTS
+void GlobalHardwareTest::encoderAChange() {
+  m_instance->encoderAChange();
+}
+#endif // AYAB_TESTS
diff --git a/src/ayab/hw_test.cpp b/src/ayab/hw_test.cpp
index 6d1738883..6aab23995 100644
--- a/src/ayab/hw_test.cpp
+++ b/src/ayab/hw_test.cpp
@@ -25,16 +25,11 @@
 #include "hw_test.h"
 #include "knitter.h"
 
-extern Knitter *knitter;
-
-// initialise static members
-SerialCommand HardwareTest::m_sCmd = SerialCommand();
-bool HardwareTest::m_autoReadOn = false;
-bool HardwareTest::m_autoTestOn = false;
-bool HardwareTest::m_timerEvent = false;
-bool HardwareTest::m_timerEventOdd = false;
-unsigned long HardwareTest::m_lastTime = 0U;
+// public interface
 
+/*!
+ * \brief Help command handler.
+ */
 void HardwareTest::helpCmd() {
   Serial.println("The following commands are available:");
   Serial.println("setSingle [0..15] [1/0]");
@@ -50,6 +45,9 @@ void HardwareTest::helpCmd() {
   Serial.println("help");
 }
 
+/*!
+ * \brief Send command handler.
+ */
 void HardwareTest::sendCmd() {
   Serial.println("Called send");
   uint8_t p[] = {1, 2, 3};
@@ -57,10 +55,6 @@ void HardwareTest::sendCmd() {
   Serial.print("\n");
 }
 
-void HardwareTest::beep() {
-  knitter->m_beeper.ready();
-}
-
 /*!
  * \brief Beep command handler.
  */
@@ -117,13 +111,6 @@ void HardwareTest::setAllCmd() {
   knitter->setSolenoids(solenoidState);
 }
 
-void HardwareTest::readEOLsensors() {
-  Serial.print("  EOL_L: ");
-  Serial.print(analogRead(EOL_PIN_L));
-  Serial.print("  EOL_R: ");
-  Serial.print(analogRead(EOL_PIN_R));
-}
-
 /*!
  * \brief Read EOL sensors command handler.
  */
@@ -133,18 +120,6 @@ void HardwareTest::readEOLsensorsCmd() {
   Serial.print("\n");
 }
 
-void HardwareTest::readEncoders() {
-  Serial.print("  ENC_A: ");
-  bool state = digitalRead(ENC_PIN_A);
-  Serial.print(state ? "HIGH" : "LOW");
-  Serial.print("  ENC_B: ");
-  state = digitalRead(ENC_PIN_B);
-  Serial.print(state ? "HIGH" : "LOW");
-  Serial.print("  ENC_C: ");
-  state = digitalRead(ENC_PIN_C);
-  Serial.print(state ? "HIGH" : "LOW");
-}
-
 /*!
  * \brief Read encoders command handler.
  */
@@ -154,13 +129,6 @@ void HardwareTest::readEncodersCmd() {
   Serial.print("\n");
 }
 
-void HardwareTest::autoRead() {
-  Serial.print("\n");
-  readEOLsensors();
-  readEncoders();
-  Serial.print("\n");
-}
-
 /*!
  * \brief Auto read command handler.
  */
@@ -169,20 +137,6 @@ void HardwareTest::autoReadCmd() {
   m_autoReadOn = true;
 }
 
-void HardwareTest::autoTestEven() {
-  Serial.println("Set even solenoids");
-  digitalWrite(LED_PIN_A, 1);
-  digitalWrite(LED_PIN_B, 1);
-  knitter->setSolenoids(0xAAAA);
-}
-
-void HardwareTest::autoTestOdd() {
-  Serial.println("Set odd solenoids");
-  digitalWrite(LED_PIN_A, 0);
-  digitalWrite(LED_PIN_B, 0);
-  knitter->setSolenoids(0x5555);
-}
-
 /*!
  * \brief Auto test command handler.
  */
@@ -191,11 +145,17 @@ void HardwareTest::autoTestCmd() {
   m_autoTestOn = true;
 }
 
+/*!
+ * \brief Stop command handler.
+ */
 void HardwareTest::stopCmd() {
   m_autoReadOn = false;
   m_autoTestOn = false;
 }
 
+/*!
+ * \brief Quit command handler.
+ */
 void HardwareTest::quitCmd() {
   knitter->setQuitFlag(true);
   knitter->setUpInterrupt();
@@ -215,25 +175,23 @@ void HardwareTest::unrecognizedCmd(const char *buffer) {
   helpCmd();
 }
 
-// Member functions
-
 /*!
- * \brief Setup for hw tests.
+ * \brief Setup for hardware tests.
  */
 void HardwareTest::setUp() {
   // set up callbacks for SerialCommand commands
-  m_sCmd.addCommand("setSingle", HardwareTest::setSingleCmd);
-  m_sCmd.addCommand("setAll", HardwareTest::setAllCmd);
-  m_sCmd.addCommand("readEOLsensors", HardwareTest::readEOLsensorsCmd);
-  m_sCmd.addCommand("readEncoders", HardwareTest::readEncodersCmd);
-  m_sCmd.addCommand("beep", HardwareTest::beepCmd);
-  m_sCmd.addCommand("autoRead", HardwareTest::autoReadCmd);
-  m_sCmd.addCommand("autoTest", HardwareTest::autoTestCmd);
-  m_sCmd.addCommand("send", HardwareTest::sendCmd);
-  m_sCmd.addCommand("stop", HardwareTest::stopCmd);
-  m_sCmd.addCommand("quit", HardwareTest::quitCmd);
-  m_sCmd.addCommand("help", HardwareTest::helpCmd);
-  m_sCmd.setDefaultHandler(HardwareTest::unrecognizedCmd);
+  m_sCmd.addCommand("setSingle", GlobalHardwareTest::setSingleCmd);
+  m_sCmd.addCommand("setAll", GlobalHardwareTest::setAllCmd);
+  m_sCmd.addCommand("readEOLsensors", GlobalHardwareTest::readEOLsensorsCmd);
+  m_sCmd.addCommand("readEncoders", GlobalHardwareTest::readEncodersCmd);
+  m_sCmd.addCommand("beep", GlobalHardwareTest::beepCmd);
+  m_sCmd.addCommand("autoRead", GlobalHardwareTest::autoReadCmd);
+  m_sCmd.addCommand("autoTest", GlobalHardwareTest::autoTestCmd);
+  m_sCmd.addCommand("send", GlobalHardwareTest::sendCmd);
+  m_sCmd.addCommand("stop", GlobalHardwareTest::stopCmd);
+  m_sCmd.addCommand("quit", GlobalHardwareTest::quitCmd);
+  m_sCmd.addCommand("help", GlobalHardwareTest::helpCmd);
+  m_sCmd.setDefaultHandler(GlobalHardwareTest::unrecognizedCmd);
 
   // Print welcome message
   Serial.print("AYAB Hardware Test, Firmware v");
@@ -248,25 +206,16 @@ void HardwareTest::setUp() {
   // attach interrupt for ENC_PIN_A(=2), interrupt #0
   detachInterrupt(0);
 #ifndef AYAB_TESTS
-  attachInterrupt(0, encoderAChange, RISING);
+  attachInterrupt(0, GlobalHardwareTest::encoderAChange, RISING);
+#endif // AYAB_TESTS
 
   m_lastTime = millis();
-#endif // AYAB_TESTS
   m_autoReadOn = false;
   m_autoTestOn = false;
   m_timerEventOdd = false;
   knitter->setQuitFlag(false);
 }
 
-#ifndef AYAB_TESTS
-/*!
- * \brief Interrupt service routine for encoder A.
- */
-void HardwareTest::encoderAChange() {
-  beep();
-}
-#endif // AYAB_TESTS
-
 /*!
  * \brief Main loop for hardware tests.
  */
@@ -278,6 +227,61 @@ void HardwareTest::loop() {
   }
 }
 
+// Private member functions
+
+void HardwareTest::beep() {
+  knitter->m_beeper.ready();
+}
+
+void HardwareTest::readEncoders() {
+  Serial.print("  ENC_A: ");
+  bool state = digitalRead(ENC_PIN_A);
+  Serial.print(state ? "HIGH" : "LOW");
+  Serial.print("  ENC_B: ");
+  state = digitalRead(ENC_PIN_B);
+  Serial.print(state ? "HIGH" : "LOW");
+  Serial.print("  ENC_C: ");
+  state = digitalRead(ENC_PIN_C);
+  Serial.print(state ? "HIGH" : "LOW");
+}
+
+void HardwareTest::readEOLsensors() {
+  Serial.print("  EOL_L: ");
+  Serial.print(analogRead(EOL_PIN_L));
+  Serial.print("  EOL_R: ");
+  Serial.print(analogRead(EOL_PIN_R));
+}
+
+void HardwareTest::autoRead() {
+  Serial.print("\n");
+  readEOLsensors();
+  readEncoders();
+  Serial.print("\n");
+}
+
+void HardwareTest::autoTestEven() {
+  Serial.println("Set even solenoids");
+  digitalWrite(LED_PIN_A, 1);
+  digitalWrite(LED_PIN_B, 1);
+  knitter->setSolenoids(0xAAAA);
+}
+
+void HardwareTest::autoTestOdd() {
+  Serial.println("Set odd solenoids");
+  digitalWrite(LED_PIN_A, 0);
+  digitalWrite(LED_PIN_B, 0);
+  knitter->setSolenoids(0x5555);
+}
+
+/*!
+ * \brief Interrupt service routine for encoder A.
+ */
+#ifndef AYAB_TESTS
+void HardwareTest::encoderAChange() {
+  beep();
+}
+#endif // AYAB_TESTS
+
 /*!
  * \brief Timer event every 500ms to handle auto functions.
  */
diff --git a/src/ayab/hw_test.h b/src/ayab/hw_test.h
index 9183c741a..b96fbff13 100644
--- a/src/ayab/hw_test.h
+++ b/src/ayab/hw_test.h
@@ -28,7 +28,31 @@
 
 #include "beeper.h"
 
-class HardwareTest {
+class HardwareTestInterface {
+public:
+  virtual ~HardwareTestInterface(){};
+
+  virtual void helpCmd() = 0;
+  virtual void sendCmd() = 0;
+  virtual void beepCmd() = 0;
+  virtual void setSingleCmd() = 0;
+  virtual void setAllCmd() = 0;
+  virtual void readEOLsensorsCmd() = 0;
+  virtual void readEncodersCmd() = 0;
+  virtual void autoReadCmd() = 0;
+  virtual void autoTestCmd() = 0;
+  virtual void stopCmd() = 0;
+  virtual void quitCmd() = 0;
+  virtual void unrecognizedCmd(const char *buffer) = 0;
+
+  virtual void setUp() = 0;
+  virtual void loop() = 0;
+#ifndef AYAB_TESTS
+  virtual void encoderAChange() = 0;
+#endif
+};
+
+class HardwareTest : public HardwareTestInterface {
 #if AYAB_TESTS
   FRIEND_TEST(HardwareTestTest, test_setUp);
   FRIEND_TEST(HardwareTestTest, test_loop_default);
@@ -37,6 +61,46 @@ class HardwareTest {
   FRIEND_TEST(HardwareTestTest, test_loop_autoTestOdd);
   friend class HardwareTestTest;
 #endif
+
+public:
+  void helpCmd();
+  void sendCmd();
+  void beepCmd();
+  void setSingleCmd();
+  void setAllCmd();
+  void readEOLsensorsCmd();
+  void readEncodersCmd();
+  void autoReadCmd();
+  void autoTestCmd();
+  void stopCmd();
+  void quitCmd();
+  void unrecognizedCmd(const char *buffer);
+
+  void setUp();
+  void loop();
+#ifndef AYAB_TESTS
+  void encoderAChange();
+#endif
+
+private:
+  void beep();
+  void readEOLsensors();
+  void readEncoders();
+  void autoRead();
+  void autoTestEven();
+  void autoTestOdd();
+  void handleTimerEvent();
+
+  SerialCommand m_sCmd = SerialCommand();
+
+  bool m_autoReadOn = false;
+  bool m_autoTestOn = false;
+
+  unsigned long m_lastTime = 0U;
+  bool m_timerEventOdd = false;
+};
+
+class GlobalHardwareTest {
 public:
   static void helpCmd();
   static void sendCmd();
@@ -53,30 +117,13 @@ class HardwareTest {
 
   static void setUp();
   static void loop();
-
-  static SerialCommand m_sCmd;
-  /* static bool m_quitFlag; */
-
-private:
-  static void beep();
-  static void readEOLsensors();
-  static void readEncoders();
-  static void autoRead();
-  static void autoTestEven();
-  static void autoTestOdd();
-  static void handleTimerEvent();
-
 #ifndef AYAB_TESTS
   static void encoderAChange();
 #endif
 
-  static bool m_autoReadOn;
-  static bool m_autoTestOn;
-
-  static unsigned long m_lastTime;
-  static bool m_timerEventOdd;
+  static HardwareTestInterface *m_instance;
 };
 
-extern HardwareTest *hwTest;
+extern GlobalHardwareTest *hwTest;
 
 #endif // HW_TEST_H_
diff --git a/src/ayab/knitter.cpp b/src/ayab/knitter.cpp
index fa30fa2e8..35eec65a5 100644
--- a/src/ayab/knitter.cpp
+++ b/src/ayab/knitter.cpp
@@ -35,7 +35,6 @@ constexpr uint16_t UINT16_MAX = 0xFFFFU;
 #endif
 
 extern Knitter *knitter;
-extern HardwareTest *hwTest;
 
 #ifndef AYAB_TESTS
 /*!
@@ -185,7 +184,7 @@ bool Knitter::startTest(Machine_t machineType) {
   if (s_init == m_opState || s_ready == m_opState) {
     m_opState = s_test;
     m_machineType = machineType;
-    HardwareTest::setUp();
+    GlobalHardwareTest::setUp();
     success = true;
   }
   return success;
@@ -344,7 +343,7 @@ void Knitter::state_test() {
     calculatePixelAndSolenoid();
     indState();
   }
-  HardwareTest::loop();
+  GlobalHardwareTest::loop();
   if (m_quitFlag) {
     m_opState = s_ready;
   }
diff --git a/src/ayab/main.cpp b/src/ayab/main.cpp
index ff0125be3..3fb1cccfb 100644
--- a/src/ayab/main.cpp
+++ b/src/ayab/main.cpp
@@ -27,17 +27,18 @@
 #include "hw_test.h"
 #include "knitter.h"
 
-// global definitions
+// global definition
 // references everywhere else must use `extern`
 Knitter *knitter;
-HardwareTest *hwTest;
+
+// initialize static member
+HardwareTestInterface *GlobalHardwareTest::m_instance = new HardwareTest();
 
 /*!
  * Setup - steps to take before going to the main loop.
  */
 void setup() {
   knitter = new Knitter();
-  hwTest = new HardwareTest();
 }
 
 /*!
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 2ac2ce66e..0ac32270b 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -53,6 +53,7 @@ set(COMMON_SOURCES
     ${PROJECT_SOURCE_DIR}/test_serial_encoding.cpp
 
     ${SOURCE_DIRECTORY}/hw_test.cpp
+    ${SOURCE_DIRECTORY}/global_hw_test.cpp
     ${PROJECT_SOURCE_DIR}/test_hw_test.cpp
     ${PROJECT_SOURCE_DIR}/mocks/SerialCommand_mock.cpp
 
@@ -68,7 +69,12 @@ set(COMMON_FLAGS
     -Wall -Wextra -Wpedantic
     -Wno-vla
     -Werror
-    -fprofile-arcs -ftest-coverage
+    -fprofile-arcs -ftest-coverage 
+    
+    # exclude global_hw_test.cpp from profile analysis
+    # to avoid tedious mocking of these simple functions
+    -fprofile-exclude-files=global_hw_test.cpp
+    
     -g -Og
     )
 set(COMMON_LINKER_FLAGS
@@ -133,6 +139,7 @@ add_board(Mega)
 add_executable(${PROJECT_NAME}_knitter
     ${PROJECT_SOURCE_DIR}/test_all.cpp
     ${SOURCE_DIRECTORY}/knitter.cpp
+    ${SOURCE_DIRECTORY}/global_hw_test.cpp
     ${PROJECT_SOURCE_DIR}/mocks/solenoids_mock.cpp
     ${PROJECT_SOURCE_DIR}/mocks/encoders_mock.cpp
     ${PROJECT_SOURCE_DIR}/mocks/beeper_mock.cpp
diff --git a/test/mocks/hw_test_mock.cpp b/test/mocks/hw_test_mock.cpp
index e25cfb5a6..c82c498ab 100644
--- a/test/mocks/hw_test_mock.cpp
+++ b/test/mocks/hw_test_mock.cpp
@@ -24,7 +24,8 @@
 #include <hw_test_mock.h>
 
 static HardwareTestMock *gHardwareTestMock = NULL;
-HardwareTestMock *hardwareTestMockInstance() {
+
+HardwareTestMock *hwTestMockInstance() {
   if (!gHardwareTestMock) {
     gHardwareTestMock = new HardwareTestMock();
   }
diff --git a/test/mocks/hw_test_mock.h b/test/mocks/hw_test_mock.h
index f317c991d..d8e60f372 100644
--- a/test/mocks/hw_test_mock.h
+++ b/test/mocks/hw_test_mock.h
@@ -27,7 +27,7 @@
 #include <gmock/gmock.h>
 #include <hw_test.h>
 
-class HardwareTestMock {
+class HardwareTestMock : public HardwareTestInterface {
 public:
   MOCK_METHOD0(helpCmd, void());
   MOCK_METHOD0(sendCmd, void());
@@ -45,7 +45,7 @@ class HardwareTestMock {
   MOCK_METHOD0(loop, void());
 };
 
-HardwareTestMock *hardwareTestMockInstance();
+HardwareTestMock *hwTestMockInstance();
 void releaseHardwareTestMock();
 
 #endif // HW_TEST_MOCK_H_
diff --git a/test/test_hw_test.cpp b/test/test_hw_test.cpp
index 026c2800a..0f6f41bcf 100644
--- a/test/test_hw_test.cpp
+++ b/test/test_hw_test.cpp
@@ -34,6 +34,9 @@ static char zero[2] = {48, 0};       // "0"
 static char two[2] = {50, 0};        // "2"
 static char twenty[3] = {50, 48, 0}; // "20"
 
+// initialize static member
+HardwareTestInterface *GlobalHardwareTest::m_instance = new HardwareTest();
+
 class HardwareTestTest : public ::testing::Test {
 protected:
   void SetUp() override {
@@ -41,6 +44,7 @@ class HardwareTestTest : public ::testing::Test {
     serialMock = serialMockInstance();
     serialCommandMock = serialCommandMockInstance();
     knitterMock = knitterMockInstance();
+    h = new HardwareTest();
   }
 
   void TearDown() override {
@@ -54,151 +58,149 @@ class HardwareTestTest : public ::testing::Test {
   SerialMock *serialMock;
   SerialCommandMock *serialCommandMock;
   KnitterMock *knitterMock;
-
-  void expect_test() {
-  }
+  HardwareTest *h;
 };
 
 TEST_F(HardwareTestTest, test_setUp) {
   EXPECT_CALL(*knitterMock, setQuitFlag);
-  ASSERT_FALSE(HardwareTest::m_autoReadOn);
-  ASSERT_FALSE(HardwareTest::m_autoTestOn);
-  ASSERT_FALSE(HardwareTest::m_timerEvent);
-  ASSERT_FALSE(HardwareTest::m_timerEventOdd);
-  HardwareTest::setUp();
+  EXPECT_CALL(*arduinoMock, millis);
+  h->setUp();
+  ASSERT_FALSE(h->m_autoReadOn);
+  ASSERT_FALSE(h->m_autoTestOn);
+  ASSERT_FALSE(h->m_timerEventOdd);
 }
 
 TEST_F(HardwareTestTest, test_helpCmd) {
-  HardwareTest::helpCmd();
+  h->helpCmd();
 }
 
 TEST_F(HardwareTestTest, test_sendCmd) {
   EXPECT_CALL(*knitterMock, send);
-  HardwareTest::sendCmd();
+  h->sendCmd();
 }
 
 TEST_F(HardwareTestTest, test_beepCmd) {
   EXPECT_CALL(*arduinoMock, analogWrite).Times(AtLeast(1));
   EXPECT_CALL(*arduinoMock, delay).Times(AtLeast(1));
-  HardwareTest::beepCmd();
+  h->beepCmd();
 }
 
 TEST_F(HardwareTestTest, test_setSingleCmd_fail1) {
   EXPECT_CALL(*serialCommandMock, next).WillOnce(Return(nullptr));
-  HardwareTest::setSingleCmd();
+  h->setSingleCmd();
 }
 
 TEST_F(HardwareTestTest, test_setSingleCmd_fail2) {
   EXPECT_CALL(*serialCommandMock, next).WillOnce(Return(twenty));
-  HardwareTest::setSingleCmd();
+  h->setSingleCmd();
 }
 
 TEST_F(HardwareTestTest, test_setSingleCmd_fail3) {
   EXPECT_CALL(*serialCommandMock, next)
       .WillOnce(Return(zero))
       .WillOnce(Return(nullptr));
-  HardwareTest::setSingleCmd();
+  h->setSingleCmd();
 }
 
 TEST_F(HardwareTestTest, test_setSingleCmd_fail4) {
   EXPECT_CALL(*serialCommandMock, next)
       .WillOnce(Return(zero))
       .WillOnce(Return(two));
-  HardwareTest::setSingleCmd();
+  h->setSingleCmd();
 }
 
 TEST_F(HardwareTestTest, test_setSingleCmd_success) {
   EXPECT_CALL(*serialCommandMock, next).WillRepeatedly(Return(zero));
   EXPECT_CALL(*knitterMock, setSolenoid);
-  HardwareTest::setSingleCmd();
+  h->setSingleCmd();
 }
 
 TEST_F(HardwareTestTest, test_setAllCmd_fail1) {
   EXPECT_CALL(*serialCommandMock, next).WillOnce(Return(nullptr));
-  HardwareTest::setAllCmd();
+  h->setAllCmd();
 }
 
 TEST_F(HardwareTestTest, test_setAllCmd_fail2) {
   EXPECT_CALL(*serialCommandMock, next)
       .WillOnce(Return(zero))
       .WillOnce(Return(nullptr));
-  HardwareTest::setAllCmd();
+  h->setAllCmd();
 }
 
 TEST_F(HardwareTestTest, test_setAllCmd_success) {
   EXPECT_CALL(*serialCommandMock, next).WillRepeatedly(Return(zero));
   EXPECT_CALL(*knitterMock, setSolenoids);
-  HardwareTest::setAllCmd();
+  h->setAllCmd();
 }
 
 TEST_F(HardwareTestTest, test_readEOLsensorsCmd) {
-  HardwareTest::readEOLsensorsCmd();
+  h->readEOLsensorsCmd();
 }
 
 TEST_F(HardwareTestTest, test_readEncodersCmd) {
   // low
   EXPECT_CALL(*arduinoMock, digitalRead).WillRepeatedly(Return(0));
-  HardwareTest::readEncodersCmd();
+  h->readEncodersCmd();
 
   // high
   EXPECT_CALL(*arduinoMock, digitalRead).WillRepeatedly(Return(1));
-  HardwareTest::readEncodersCmd();
+  h->readEncodersCmd();
 }
 
 TEST_F(HardwareTestTest, test_autoReadCmd) {
-  HardwareTest::autoReadCmd();
+  h->autoReadCmd();
 }
 
 TEST_F(HardwareTestTest, test_autoTestCmd) {
-  HardwareTest::autoTestCmd();
+  h->autoTestCmd();
 }
 
 TEST_F(HardwareTestTest, test_stopCmd) {
-  HardwareTest::stopCmd();
+  h->stopCmd();
 }
 
 TEST_F(HardwareTestTest, test_quitCmd) {
   EXPECT_CALL(*knitterMock, setQuitFlag);
-  HardwareTest::quitCmd();
+  h->quitCmd();
 }
 
 TEST_F(HardwareTestTest, test_unrecognizedCmd) {
   const char buffer[1] = {1};
-  HardwareTest::unrecognizedCmd(buffer);
+  h->unrecognizedCmd(buffer);
 }
 
 TEST_F(HardwareTestTest, test_loop_default) {
-  HardwareTest::m_lastTime = 0;
+  h->m_lastTime = 0;
   EXPECT_CALL(*arduinoMock, millis).WillOnce(Return(499));
-  HardwareTest::loop();
+  h->loop();
 }
 
-TEST_F(HardwareTestTest, test_loop_autoRead) {
-  HardwareTest::m_lastTime = 0;
+TEST_F(HardwareTestTest, test_nullTimerEvent) {
+  h->m_lastTime = 0;
   EXPECT_CALL(*arduinoMock, millis).WillOnce(Return(500));
-  HardwareTest::m_timerEventOdd = true;
-  HardwareTest::m_autoReadOn = true;
-  EXPECT_CALL(*arduinoMock, analogRead).Times(2);
-  EXPECT_CALL(*arduinoMock, digitalRead).Times(3);
-  HardwareTest::loop();
+  h->m_autoReadOn = false;
+  h->m_autoTestOn = false;
+  h->loop();
 }
 
 TEST_F(HardwareTestTest, test_loop_autoTestEven) {
-  HardwareTest::m_lastTime = 0;
+  h->m_lastTime = 0;
   EXPECT_CALL(*arduinoMock, millis).WillOnce(Return(500));
-  HardwareTest::m_timerEventOdd = false;
-  HardwareTest::m_autoTestOn = true;
+  h->m_timerEventOdd = false;
+  h->m_autoReadOn = true;
+  h->m_autoTestOn = true;
   EXPECT_CALL(*arduinoMock, digitalWrite).Times(2);
   EXPECT_CALL(*knitterMock, setSolenoids);
-  HardwareTest::loop();
+  h->loop();
 }
 
 TEST_F(HardwareTestTest, test_loop_autoTestOdd) {
-  HardwareTest::m_lastTime = 0;
+  h->m_lastTime = 0;
   EXPECT_CALL(*arduinoMock, millis).WillOnce(Return(500));
-  HardwareTest::m_timerEventOdd = true;
-  HardwareTest::m_autoTestOn = true;
+  h->m_timerEventOdd = true;
+  h->m_autoReadOn = true;
+  h->m_autoTestOn = true;
   EXPECT_CALL(*arduinoMock, digitalWrite).Times(2);
   EXPECT_CALL(*knitterMock, setSolenoids);
-  HardwareTest::loop();
+  h->loop();
 }
diff --git a/test/test_knitter.cpp b/test/test_knitter.cpp
index 5e6dfae54..644fad2b1 100644
--- a/test/test_knitter.cpp
+++ b/test/test_knitter.cpp
@@ -33,12 +33,15 @@
 
 using ::testing::_;
 using ::testing::AtLeast;
+using ::testing::Mock;
 using ::testing::Return;
 
 // global definitions
 // references everywhere else must use `extern`
 Knitter *knitter;
-HardwareTest *hwTest;
+
+// initialize static member
+HardwareTestInterface *GlobalHardwareTest::m_instance = new HardwareTestMock();
 
 void onPacketReceived(const uint8_t *buffer, size_t size) {
   (void)buffer;
@@ -53,7 +56,9 @@ class KnitterTest : public ::testing::Test {
     solenoidsMock = solenoidsMockInstance();
     encodersMock = encodersMockInstance();
     serialEncodingMock = serialEncodingMockInstance();
-    hwTestMock = hardwareTestMockInstance();
+    hwTestMock =
+        static_cast<HardwareTestMock *>(GlobalHardwareTest::m_instance);
+    Mock::AllowLeak(hwTestMock); // because it does not get destructed
     expect_constructor();
     k = new Knitter();
   }
@@ -73,7 +78,8 @@ class KnitterTest : public ::testing::Test {
   EncodersMock *encodersMock;
   SerialEncodingMock *serialEncodingMock;
   HardwareTestMock *hwTestMock;
-  Knitter *&k = knitter; // `k` is alias of global `knitter`
+  HardwareTestMock *dummy;
+  Knitter *&k = knitter; // alias of global `knitter`
 
   void expect_constructor() {
     EXPECT_CALL(*arduinoMock, pinMode(ENC_PIN_A, INPUT));
@@ -182,6 +188,7 @@ class KnitterTest : public ::testing::Test {
     expect_indState();
     EXPECT_CALL(*hwTestMock, loop);
     expected_fsm();
+    ASSERT_TRUE(Mock::VerifyAndClear(hwTestMock));
   }
 
   void expected_set_machine(Machine_t machineType) {
@@ -303,6 +310,8 @@ TEST_F(KnitterTest, test_fsm_test) {
   expect_indState<0>();
   EXPECT_CALL(*hwTestMock, loop);
   expected_fsm();
+
+  ASSERT_TRUE(Mock::VerifyAndClear(hwTestMock));
 }
 
 /*!
@@ -373,6 +382,7 @@ TEST_F(KnitterTest, test_startTest) {
   EXPECT_CALL(*hwTestMock, setUp);
   ASSERT_EQ(k->startTest(Kh910), true);
   ASSERT_EQ(k->getState(), s_test);
+  ASSERT_TRUE(Mock::VerifyAndClear(hwTestMock));
 }
 
 /*!
@@ -684,6 +694,8 @@ TEST_F(KnitterTest, test_calculatePixelAndSolenoid) {
   // K carriage direction right
   expected_isr(END_RIGHT[Kh270], Right, Left, Regular, Knit);
   expected_test();
+
+  ASSERT_TRUE(Mock::VerifyAndClear(hwTestMock));
 }
 
 /*!
@@ -724,6 +736,7 @@ TEST_F(KnitterTest, test_quit_hw_test) {
   EXPECT_CALL(*hwTestMock, loop);
   k->state_test();
   ASSERT_EQ(k->getState(), s_ready);
+  ASSERT_TRUE(Mock::VerifyAndClear(hwTestMock));
 }
 
 /*!