diff --git a/boot/boot_serial/src/boot_serial.c b/boot/boot_serial/src/boot_serial.c
index 9b63043..6257613 100644
--- a/boot/boot_serial/src/boot_serial.c
+++ b/boot/boot_serial/src/boot_serial.c
@@ -71,7 +71,7 @@
 #endif
 static char in_buf[BOOT_SERIAL_INPUT_MAX + 1];
 static char dec_buf[BOOT_SERIAL_INPUT_MAX + 1];
-static const struct boot_uart_funcs *boot_uf;
+const struct boot_uart_funcs *boot_uf;
 static uint32_t curr_off;
 static uint32_t img_size;
 static struct nmgr_hdr *bs_hdr;
diff --git a/boot/boot_serial/src/boot_serial_priv.h b/boot/boot_serial/src/boot_serial_priv.h
index 3b4c1ec..9275f3f 100644
--- a/boot/boot_serial/src/boot_serial_priv.h
+++ b/boot/boot_serial/src/boot_serial_priv.h
@@ -63,6 +63,7 @@
 #define IMGMGR_NMGR_ID_UPLOAD           1
 
 void boot_serial_input(char *buf, int len);
+extern const struct boot_uart_funcs *boot_uf;
 
 #ifdef __cplusplus
 }
diff --git a/boot/boot_serial/test/src/boot_test.c b/boot/boot_serial/test/src/boot_test.c
index 3beb379..e8deb7e 100644
--- a/boot/boot_serial/test/src/boot_test.c
+++ b/boot/boot_serial/test/src/boot_test.c
@@ -31,6 +31,7 @@
 #include "hal/hal_flash.h"
 #include "flash_map_backend/flash_map_backend.h"
 
+#include "boot_serial/boot_serial.h"
 #include "boot_serial_priv.h"
 
 TEST_CASE_DECL(boot_serial_setup)
@@ -39,6 +40,15 @@
 TEST_CASE_DECL(boot_serial_img_msg)
 TEST_CASE_DECL(boot_serial_upload_bigger_image)
 
+static void
+test_uart_write(const char *str, int len)
+{
+}
+
+static const struct boot_uart_funcs test_uart = {
+    .write = test_uart_write
+};
+
 void
 tx_msg(void *src, int len)
 {
@@ -57,6 +67,7 @@
 int
 boot_serial_test(void)
 {
+    boot_uf = &test_uart;
     boot_serial_suite();
     return tu_any_failed;
 }
diff --git a/boot/boot_serial/test/src/testcases/boot_serial_empty_msg.c b/boot/boot_serial/test/src/testcases/boot_serial_empty_msg.c
index a4bd470..12b6457 100644
--- a/boot/boot_serial/test/src/testcases/boot_serial_empty_msg.c
+++ b/boot/boot_serial/test/src/testcases/boot_serial_empty_msg.c
@@ -23,8 +23,6 @@
     char buf[4];
     struct nmgr_hdr hdr;
 
-    boot_serial_input(buf, 0);
-
     tx_msg(buf, 0);
 
     strcpy(buf, "--");