diff --git a/python/test/test_api.py b/python/test/test_api.py
index 86eb619..a600983 100644
--- a/python/test/test_api.py
+++ b/python/test/test_api.py
@@ -155,7 +155,7 @@ del test_file
 #==========================================================#
 
 # open previously created TREXIO file, now in 'read' mode
-test_file2 = trexio.File(output_filename, 'r', TEST_TREXIO_BACKEND)
+test_file2 = trexio.File(output_filename, 'r', trexio.TREXIO_AUTO)
 assert test_file2.exists
 
 # check for existence of some of the previously written variables
diff --git a/tests/io_all.c b/tests/io_all.c
index d2d1ed2..e476efd 100644
--- a/tests/io_all.c
+++ b/tests/io_all.c
@@ -163,7 +163,7 @@ int test_read(const char* file_name, const back_end_t backend) {
 /*================= START OF TEST ==================*/
 
   // open existing file on 'read' mode [created by test_write]
-  file = trexio_open(file_name, 'r', backend, &rc);
+  file = trexio_open(file_name, 'r', TREXIO_AUTO, &rc);
   assert (file != NULL);
 
   // read nucleus_num
diff --git a/tests/open_hdf5.c b/tests/open_hdf5.c
index 7f4ec62..d0a6581 100644
--- a/tests/open_hdf5.c
+++ b/tests/open_hdf5.c
@@ -57,6 +57,30 @@ static int test_open_r (const char* file_name, const back_end_t backend) {
 }
 
 
+static int test_open_auto (const char* file_name) {
+
+/* Try to open the TREXIO file in 'read' mode */
+
+  trexio_t* file = NULL;
+  trexio_exit_code rc;
+
+/*================= START OF TEST ==================*/
+
+  // open file in 'write' mode
+  file = trexio_open(file_name, 'r', TREXIO_AUTO, &rc);
+  assert (file != NULL);
+  assert (rc == TREXIO_SUCCESS);
+
+  // close current session
+  rc = trexio_close(file);
+  assert (rc == TREXIO_SUCCESS);
+
+/*================= END OF TEST ==================*/
+
+  return 0;
+}
+
+
 static int test_open_errors (const back_end_t backend) {
 
 /* Try to call trexio_open with bad arguments */
@@ -128,6 +152,7 @@ int main(void) {
 
   test_open_w     (TREXIO_FILE, TEST_BACKEND);
   test_open_r     (TREXIO_FILE, TEST_BACKEND);
+  test_open_auto  (TREXIO_FILE);
   test_open_errors(TEST_BACKEND);
   test_inquire    (TEST_BACKEND);
 
diff --git a/tests/open_text.c b/tests/open_text.c
index 4ec7810..130ba91 100644
--- a/tests/open_text.c
+++ b/tests/open_text.c
@@ -57,6 +57,30 @@ static int test_open_r (const char* file_name, const back_end_t backend) {
 }
 
 
+static int test_open_auto (const char* file_name) {
+
+/* Try to open the TREXIO file in 'read' mode */
+
+  trexio_t* file = NULL;
+  trexio_exit_code rc;
+
+/*================= START OF TEST ==================*/
+
+  // open file in 'write' mode
+  file = trexio_open(file_name, 'r', TREXIO_AUTO, &rc);
+  assert (file != NULL);
+  assert (rc == TREXIO_SUCCESS);
+
+  // close current session
+  rc = trexio_close(file);
+  assert (rc == TREXIO_SUCCESS);
+
+/*================= END OF TEST ==================*/
+
+  return 0;
+}
+
+
 static int test_open_errors (const back_end_t backend) {
 
 /* Try to call trexio_open with bad arguments */
@@ -128,6 +152,7 @@ int main(void) {
 
   test_open_w     (TREXIO_FILE, TEST_BACKEND);
   test_open_r     (TREXIO_FILE, TEST_BACKEND);
+  test_open_auto  (TREXIO_FILE);
   test_open_errors(TEST_BACKEND);
   test_inquire    (TEST_BACKEND);
 
diff --git a/tests/test_f.f90 b/tests/test_f.f90
index e7d4ee1..bc227ad 100644
--- a/tests/test_f.f90
+++ b/tests/test_f.f90
@@ -226,7 +226,7 @@ subroutine test_read(file_name, back_end)
   rc = trexio_inquire(file_name)
   call trexio_assert(rc, TREXIO_SUCCESS)
 
-  trex_file = trexio_open(file_name, 'r', back_end, rc)
+  trex_file = trexio_open(file_name, 'r', TREXIO_AUTO, rc)
   call trexio_assert(rc, TREXIO_SUCCESS)
 
   rc = trexio_read_nucleus_num(trex_file, num_read)