diff --git a/.vscode/c_cpp_properties.json b/.vscode/c_cpp_properties.json
new file mode 100644
index 0000000..5703028
--- /dev/null
+++ b/.vscode/c_cpp_properties.json
@@ -0,0 +1,17 @@
+{
+    "configurations": [
+        {
+            "name": "Linux",
+            "includePath": [
+                "${workspaceFolder}/**",
+                "/usr/include/libftdi1"
+            ],
+            "defines": [],
+            "compilerPath": "/usr/bin/clang",
+            "cStandard": "c11",
+            "cppStandard": "c++17",
+            "intelliSenseMode": "clang-x64"
+        }
+    ],
+    "version": 4
+}
\ No newline at end of file
diff --git a/src/gpio.c b/src/gpio.c
index e87b8d8..238a81d 100644
--- a/src/gpio.c
+++ b/src/gpio.c
@@ -9,7 +9,7 @@ static int ftdi_open(const struct gpio *gpio)
 {
     int res;
 
-    if((gpio->ftdi_dev->ftdi = ftdi_new()) == 0) {
+    if((gpio->ftdi_dev->ftdi = ftdi_new()) == NULL) {
         syslog(LOG_ERR, "ftdi_new failed\n");
         return EXIT_FAILURE;
     }
@@ -35,7 +35,7 @@ static int ftdi_open(const struct gpio *gpio)
 int gpio_open(const struct gpio *gpio)
 {
     int res;
-    unsigned int init_value = 0;
+    unsigned char init_value = 0;
 
     if(NULL == gpio) {
         syslog(LOG_ERR, "No valid gpio object given.\n");
@@ -50,7 +50,6 @@ int gpio_open(const struct gpio *gpio)
     }
 
     gpio->ftdi_dev->bit_mask |= (unsigned char)gpio->pin;
-    syslog(LOG_DEBUG, "bitmask: 0x%02x\n", gpio->ftdi_dev->bit_mask);
     res = ftdi_set_bitmode(gpio->ftdi_dev->ftdi, gpio->ftdi_dev->bit_mask, BITMODE_BITBANG);
     if(res < 0) {
         syslog(LOG_ERR, "unable to set bit bang mode: %d (%s)\n", res,
@@ -60,7 +59,7 @@ int gpio_open(const struct gpio *gpio)
         return EXIT_FAILURE;
     }
 
-    res = gpio_write(gpio, init_value);
+    res = ftdi_write_data(gpio->ftdi_dev->ftdi, &init_value, 1);
     if(res < 0) {
         syslog(LOG_ERR, "unable to write to gpio %u (%s)\n", gpio->pin,
                ftdi_get_error_string(gpio->ftdi_dev->ftdi));
@@ -85,6 +84,7 @@ int gpio_close(const struct gpio *gpio)
     if(gpio->ftdi_dev->bit_mask == 0) {
         ftdi_usb_close(gpio->ftdi_dev->ftdi);
         ftdi_free(gpio->ftdi_dev->ftdi);
+        gpio->ftdi_dev->is_open = false;
     }
 
     return EXIT_SUCCESS;
diff --git a/test/inc/mock_ftdi.h b/test/inc/mock_ftdi.h
new file mode 100644
index 0000000..cb56bb0
--- /dev/null
+++ b/test/inc/mock_ftdi.h
@@ -0,0 +1,18 @@
+#ifndef __MOCK_FTDI_H__
+#define __MOCK_FTDI_H__
+
+#include <fff.h>
+
+DEFINE_FFF_GLOBALS;
+
+DECLARE_FAKE_VOID_FUNC(ftdi_free, struct ftdi_context *);
+
+DECLARE_FAKE_VALUE_FUNC(int, ftdi_usb_open, struct ftdi_context *, int, int);
+DECLARE_FAKE_VALUE_FUNC(int, ftdi_usb_close, struct ftdi_context *);
+DECLARE_FAKE_VALUE_FUNC(struct ftdi_context *, ftdi_new);
+DECLARE_FAKE_VALUE_FUNC(const char *, ftdi_get_error_string, struct ftdi_context *);
+DECLARE_FAKE_VALUE_FUNC(int, ftdi_set_bitmode, struct ftdi_context *, unsigned char, unsigned char);
+DECLARE_FAKE_VALUE_FUNC(int, ftdi_read_data, struct ftdi_context *, unsigned char *, int);
+DECLARE_FAKE_VALUE_FUNC(int, ftdi_write_data, struct ftdi_context *, const unsigned char *, int);
+
+#endif
diff --git a/test/unit/gpio_close.c b/test/unit/gpio_close.c
new file mode 100644
index 0000000..457c864
--- /dev/null
+++ b/test/unit/gpio_close.c
@@ -0,0 +1,27 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+#include <mock_ftdi.h>
+
+#include <ftdi_dev.h>
+#include <gpio.h>
+
+UTEST(gpio_close, invalid_gpio_obj) {
+    ASSERT_EQ(gpio_close(NULL), EXIT_FAILURE);
+}
+
+UTEST(gpio_close, empty_bitmask) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.is_open = true;
+    ftdi_obj.bit_mask = 0x08;
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+    ASSERT_EQ(gpio_close(&gpio_1), EXIT_SUCCESS);
+
+}
\ No newline at end of file
diff --git a/test/unit/gpio_open.c b/test/unit/gpio_open.c
new file mode 100644
index 0000000..c4297d3
--- /dev/null
+++ b/test/unit/gpio_open.c
@@ -0,0 +1,159 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+#include <mock_ftdi.h>
+
+#include <ftdi_dev.h>
+#include <gpio.h>
+
+UTEST(gpio_open, invalid_ftdi_new_result) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = NULL;
+
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, ftdi_usb_open_failed) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = -1;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, ftdi_read_data_failed) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = 0;
+    ftdi_read_data_fake.return_val = -1;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, ftdi_open_success) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = 0;
+    ftdi_read_data_fake.return_val = 0;
+    ftdi_set_bitmode_fake.return_val = 0;
+    ftdi_write_data_fake.return_val = 0;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_SUCCESS);
+}
+
+UTEST(gpio_open, invalid_gpio_obj) {
+    ASSERT_EQ(gpio_open(NULL), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, ftdi_set_bitmode_failed) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = 0;
+    ftdi_read_data_fake.return_val = 0;
+    ftdi_set_bitmode_fake.return_val = -1;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, ftdi_write_data_failed) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = 0;
+    ftdi_read_data_fake.return_val = 0;
+    ftdi_set_bitmode_fake.return_val = 0;
+    ftdi_write_data_fake.return_val = -1;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_open, success) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+    struct ftdi_context ftdi_ctx;
+    ftdi_obj.ftdi = NULL,
+    ftdi_obj.is_open = false,
+    ftdi_obj.vendor_id = 0x0403,
+    ftdi_obj.product_id = 0x6001,
+    ftdi_obj.bit_mask = 0,
+    ftdi_obj.status_mask = 0,
+
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_new_fake.return_val = &ftdi_ctx;
+    ftdi_usb_open_fake.return_val = 0;
+    ftdi_read_data_fake.return_val = 0;
+    ftdi_set_bitmode_fake.return_val = 0;
+    ftdi_write_data_fake.return_val = 0;
+    ASSERT_EQ(gpio_open(&gpio_1), EXIT_SUCCESS);
+}
diff --git a/test/unit/gpio_read.c b/test/unit/gpio_read.c
new file mode 100644
index 0000000..a110f22
--- /dev/null
+++ b/test/unit/gpio_read.c
@@ -0,0 +1,45 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+#include <mock_ftdi.h>
+
+#include <ftdi_dev.h>
+#include <gpio.h>
+
+#include <stdio.h>
+
+UTEST(gpio_read, invalid_params) {
+
+    ASSERT_EQ(gpio_read(NULL, NULL), EXIT_FAILURE);
+}
+
+UTEST(gpio_read, value_0) {
+    unsigned int result;
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = ~0x08;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ASSERT_EQ(gpio_read(&gpio_1, &result), EXIT_SUCCESS);
+    result = ((ftdi_obj.status_mask) & (gpio_1.pin)) >> 3;
+    ASSERT_EQ(result, 0)
+}
+
+UTEST(gpio_read, value_1) {
+    unsigned int result;
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0x08;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ASSERT_EQ(gpio_read(&gpio_1, &result), EXIT_SUCCESS);
+    result = ((ftdi_obj.status_mask) & (gpio_1.pin)) >> 3;
+    ASSERT_EQ(result, 1)
+}
diff --git a/test/unit/gpio_toggle.c b/test/unit/gpio_toggle.c
new file mode 100644
index 0000000..afd91aa
--- /dev/null
+++ b/test/unit/gpio_toggle.c
@@ -0,0 +1,43 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+#include <mock_ftdi.h>
+
+#include <ftdi_dev.h>
+#include <gpio.h>
+
+#include <stdio.h>
+
+UTEST(gpio_toggle, invalid_params) {
+
+    ASSERT_EQ(gpio_toggle(NULL), EXIT_FAILURE);
+}
+
+UTEST(gpio_toggle, ftdi_write_data_fails) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_write_data_fake.return_val = -1;
+
+    ASSERT_EQ(gpio_toggle(&gpio_1), EXIT_FAILURE);
+}
+
+UTEST(gpio_toggle, success) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_write_data_fake.return_val = 0;
+
+    ASSERT_EQ(gpio_toggle(&gpio_1), EXIT_SUCCESS);
+}
diff --git a/test/unit/gpio_write.c b/test/unit/gpio_write.c
new file mode 100644
index 0000000..ee0abac
--- /dev/null
+++ b/test/unit/gpio_write.c
@@ -0,0 +1,60 @@
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+#include <mock_ftdi.h>
+
+#include <ftdi_dev.h>
+#include <gpio.h>
+
+UTEST(gpio_write, invalid_params) {
+
+    ASSERT_EQ(gpio_write(NULL, 0), EXIT_FAILURE);
+}
+
+UTEST(gpio_write, value_0) {
+    unsigned int result;
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0xff;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_write_data_fake.return_val = 0;
+
+    ASSERT_EQ(gpio_write(&gpio_1, 0), EXIT_SUCCESS);
+    result = ((ftdi_obj.status_mask) & (gpio_1.pin)) >> 3;
+    ASSERT_EQ(result, 0)
+}
+
+UTEST(gpio_write, value_1) {
+    unsigned int result;
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_write_data_fake.return_val = 0;
+
+    ASSERT_EQ(gpio_write(&gpio_1, 1), EXIT_SUCCESS);
+    result = ((ftdi_obj.status_mask) | (gpio_1.pin)) >> 3;
+    ASSERT_EQ(result, 1)
+}
+
+UTEST(gpio_write, ftdi_write_data_failed) {
+    struct gpio gpio_1;
+    struct ftdi_dev ftdi_obj;
+
+    ftdi_obj.status_mask = 0;
+    gpio_1.pin = 0x08;
+    gpio_1.ftdi_dev = &ftdi_obj;
+
+    ftdi_write_data_fake.return_val = -1;
+
+    ASSERT_EQ(gpio_write(&gpio_1, 0), EXIT_FAILURE);
+}
diff --git a/test/unit/main.c b/test/unit/main.c
new file mode 100644
index 0000000..40e82ff
--- /dev/null
+++ b/test/unit/main.c
@@ -0,0 +1,8 @@
+#include <stdlib.h>
+#include <time.h>
+#include <sys/syscall.h>
+
+#include <utest.h>
+
+UTEST_MAIN();
+
diff --git a/test/unit/mock_ftdi.c b/test/unit/mock_ftdi.c
new file mode 100644
index 0000000..f1062e5
--- /dev/null
+++ b/test/unit/mock_ftdi.c
@@ -0,0 +1,13 @@
+#include <mock_ftdi.h>
+
+DEFINE_FFF_GLOBALS;
+
+DEFINE_FAKE_VOID_FUNC(ftdi_free, struct ftdi_context *);
+
+DEFINE_FAKE_VALUE_FUNC(int, ftdi_usb_open, struct ftdi_context *, int, int);
+DEFINE_FAKE_VALUE_FUNC(int, ftdi_usb_close, struct ftdi_context *);
+DEFINE_FAKE_VALUE_FUNC(struct ftdi_context *, ftdi_new);
+DEFINE_FAKE_VALUE_FUNC(const char *, ftdi_get_error_string, struct ftdi_context *);
+DEFINE_FAKE_VALUE_FUNC(int, ftdi_set_bitmode, struct ftdi_context *, unsigned char, unsigned char);
+DEFINE_FAKE_VALUE_FUNC(int, ftdi_read_data, struct ftdi_context *, unsigned char *, int);
+DEFINE_FAKE_VALUE_FUNC(int, ftdi_write_data, struct ftdi_context *, const unsigned char *, int);
diff --git a/test/unit/test_gpio.c b/test/unit/test_gpio.c
deleted file mode 100644
index 2e6a1cb..0000000
--- a/test/unit/test_gpio.c
+++ /dev/null
@@ -1,46 +0,0 @@
-#include <assert.h>
-#include <stdlib.h>
-#include <stdbool.h>
-#include <time.h>
-#include <sys/syscall.h>
-
-#include <fff.h>
-#include <utest.h>
-
-#include <ftdi_dev.h>
-#include <gpio.h>
-
-DEFINE_FFF_GLOBALS;
-
-FAKE_VOID_FUNC(ftdi_free, struct ftdi_context *);
-
-FAKE_VALUE_FUNC(int, ftdi_usb_open, struct ftdi_context *, int, int);
-FAKE_VALUE_FUNC(int, ftdi_usb_close, struct ftdi_context *);
-FAKE_VALUE_FUNC(struct ftdi_context *, ftdi_new);
-FAKE_VALUE_FUNC(const char *, ftdi_get_error_string, struct ftdi_context *);
-FAKE_VALUE_FUNC(int, ftdi_set_bitmode, struct ftdi_context *, unsigned char, unsigned char);
-FAKE_VALUE_FUNC(int, ftdi_read_data, struct ftdi_context *, unsigned char *, int);
-FAKE_VALUE_FUNC(int, ftdi_write_data, struct ftdi_context *, const unsigned char *, int);
-
-UTEST_MAIN();
-
-UTEST(gpio, gpio_open) {
-    struct gpio gpio_1;
-    struct ftdi_dev ftdi_obj;
-    struct ftdi_context ftdi_ctx;
-
-    ftdi_obj.ftdi = NULL,
-    ftdi_obj.is_open = false,
-    ftdi_obj.vendor_id = 0x0403,
-    ftdi_obj.product_id = 0x6001,
-    ftdi_obj.bit_mask = 0,
-    ftdi_obj.status_mask = 0,
-
-    gpio_1.pin = 0x08;
-    gpio_1.ftdi_dev = &ftdi_obj;
-
-    ASSERT_EQ(gpio_open(NULL), EXIT_FAILURE);
-
-    ftdi_new_fake.return_val = &ftdi_ctx;
-    ASSERT_EQ(gpio_open(&gpio_1), EXIT_SUCCESS);
-}