diff --git a/Makefile.am b/Makefile.am
index e833fab..50c8681 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -191,7 +191,7 @@ setup_py      = $(srcdir)/python/setup.py
 setup_cfg     = $(srcdir)/python/setup.cfg
 pytrexio_py   = $(srcdir)/python/pytrexio/pytrexio.py
 trexio_py     = $(srcdir)/python/trexio.py
-TEST_PY       = $(srcdir)/python/test/test_api.py
+TEST_PY       = python/test/test_api.py
 pytrexio_c    = $(srcdir)/src/pytrexio_wrap.c
 pytrexio_i    = $(srcdir)/src/pytrexio.i
 numpy_i       = $(srcdir)/src/numpy.i
diff --git a/python/test/test_api.py b/python/test/test_api.py
index a97b87e..5f23a91 100644
--- a/python/test/test_api.py
+++ b/python/test/test_api.py
@@ -1,8 +1,10 @@
+#!/usr/bin/env python3
+
 import os
 import shutil
 import numpy as np
 
-import trexio as tr
+import trexio
 
 #=========================================================#
 #======== SETUP THE BACK END AND OUTPUT FILE NAME ========#
@@ -15,9 +17,9 @@ OUTPUT_FILENAME_HDF5 = 'test_py_swig.h5'
 
 
 # define TREXIO file name
-if TEST_TREXIO_BACKEND == tr.TREXIO_HDF5:
+if TEST_TREXIO_BACKEND == trexio.TREXIO_HDF5:
     output_filename = OUTPUT_FILENAME_HDF5
-elif TEST_TREXIO_BACKEND == tr.TREXIO_TEXT:
+elif TEST_TREXIO_BACKEND == trexio.TREXIO_TEXT:
     output_filename = OUTPUT_FILENAME_TEXT
 else:
     raise ValueError ('Specify one of the supported back ends as TEST_TREXIO_BACKEND')
@@ -25,9 +27,9 @@ else:
 
 # remove TREXIO file if exists in the current directory
 try:
-    if TEST_TREXIO_BACKEND == tr.TREXIO_HDF5:
+    if TEST_TREXIO_BACKEND == trexio.TREXIO_HDF5:
         os.remove(output_filename)
-    elif TEST_TREXIO_BACKEND == tr.TREXIO_TEXT:
+    elif TEST_TREXIO_BACKEND == trexio.TREXIO_TEXT:
         shutil.rmtree(output_filename)
 except:
     print ('Nothing to remove.')
@@ -39,16 +41,29 @@ except:
 
 
 # create TREXIO file and open it for writing
-#test_file = tr.open(output_filename, 'w', TEST_TREXIO_BACKEND)
-test_file = tr.File(output_filename, mode='w', back_end=TEST_TREXIO_BACKEND)
+#test_file = trexio.open(output_filename, 'w', TEST_TREXIO_BACKEND)
+test_file = trexio.File(output_filename, mode='w', back_end=TEST_TREXIO_BACKEND)
 
-# Print docstring of the tr.open function
-#print(tr.open.__doc__)
+# Print docstring of the trexio.open function
+#print(trexio.open.__doc__)
 
 nucleus_num = 12
 
+try:
+    trexio.write_nucleus_num(test_file, -100)
+except trexio.Error:
+    print("Writing negative nucleus_num: checked.")
+
 # write nucleus_num in the file
-tr.write_nucleus_num(test_file, nucleus_num)
+try:
+    trexio.write_nucleus_num(test_file, nucleus_num)
+except:
+    raise
+
+try:
+    trexio.write_nucleus_num(test_file, nucleus_num*2)
+except trexio.Error:
+    print("Attempt to overwrite nucleus_num: checked.")
 
 # initialize charge arrays as a list and convert it to numpy array
 charges = [6., 6., 6., 6., 6., 6., 1., 1., 1., 1., 1., 1.]
@@ -57,7 +72,7 @@ charges_np = np.array(charges, dtype=np.int32)
 
 # function call below works with both lists and numpy arrays, dimension needed for memory-safety is derived 
 # from the size of the list/array by SWIG using typemaps from numpy.i
-tr.write_nucleus_charge(test_file, charges_np)
+trexio.write_nucleus_charge(test_file, charges_np)
 
 # initialize arrays of nuclear indices as a list and convert it to numpy array
 indices = [i for i in range(nucleus_num)]
@@ -66,7 +81,7 @@ indices_np = np.array(indices, dtype=np.int64)
 
 # function call below works with both lists and numpy arrays, dimension needed for memory-safety is derived 
 # from the size of the list/array by SWIG using typemacs from numpy.i
-tr.write_basis_nucleus_index(test_file, indices_np)
+trexio.write_basis_nucleus_index(test_file, indices_np)
 
 # initialize a list of nuclear coordinates
 coords = [
@@ -85,12 +100,12 @@ coords = [
   ]
 
 # write coordinates in the file
-tr.write_nucleus_coord(test_file, coords)
+trexio.write_nucleus_coord(test_file, coords)
 
 point_group = 'B3U'
 
 # write nucleus_point_group in the file
-tr.write_nucleus_point_group(test_file, point_group)
+trexio.write_nucleus_point_group(test_file, point_group)
 
 labels = [
         'C',
@@ -107,13 +122,13 @@ labels = [
         'H']
 
 # write nucleus_label in the file
-tr.write_nucleus_label(test_file,labels)
+trexio.write_nucleus_label(test_file,labels)
 
 # close TREXIO file 
 # [TODO:] this functional call is no longer needed as we introduced TREXIO_File class which has a desctructor that closes the file
-#tr.close(test_file)
+#trexio.close(test_file)
 # [TODO:] without calling destructor on test_file the TREXIO_FILE is not getting created and the data is not written when using TEXT back end. This, the user still has to explicitly call destructor on test_file object instead 
-# tr.close function. This is only an issue when the data is getting written and read in the same session (e.g. in Jupyter notebook)
+# trexio.close function. This is only an issue when the data is getting written and read in the same session (e.g. in Jupyter notebook)
 del test_file
 
 
@@ -123,68 +138,68 @@ del test_file
 #==========================================================#
 
 # open previously created TREXIO file, now in 'read' mode
-#test_file2 = tr.open(output_filename, 'r', TEST_TREXIO_BACKEND)
-test_file2 = tr.File(output_filename, 'r', TEST_TREXIO_BACKEND)
+#test_file2 = trexio.open(output_filename, 'r', TEST_TREXIO_BACKEND)
+test_file2 = trexio.File(output_filename, 'r', TEST_TREXIO_BACKEND)
 
 # read nucleus_num from file
-rnum = tr.read_nucleus_num(test_file2)
+rnum = trexio.read_nucleus_num(test_file2)
 assert rnum==nucleus_num
 
 # safe call to read_nucleus_charge array of float values
-rcharges_np = tr.read_nucleus_charge(test_file2, dim=nucleus_num)
+rcharges_np = trexio.read_nucleus_charge(test_file2, dim=nucleus_num)
 assert rcharges_np.dtype is np.dtype(np.float64)
 np.testing.assert_array_almost_equal(rcharges_np, charges_np, decimal=8)
 
 # unsafe call to read_safe should fail with error message corresponding to TREXIO_UNSAFE_ARRAY_DIM
 try:
-    rcharges_fail = tr.read_nucleus_charge(test_file2, dim=nucleus_num*5)
+    rcharges_fail = trexio.read_nucleus_charge(test_file2, dim=nucleus_num*5)
 except Exception:
     print("Unsafe call to safe API: checked")
 
 # safe call to read array of int values (nuclear indices)
-rindices_np_16 = tr.read_basis_nucleus_index(test_file2, dim=nucleus_num, dtype=np.int16)
+rindices_np_16 = trexio.read_basis_nucleus_index(test_file2, dim=nucleus_num, dtype=np.int16)
 assert rindices_np_16.dtype is np.dtype(np.int16)
 for i in range(nucleus_num):
     assert rindices_np_16[i]==indices_np[i]
 
-rindices_np_32 = tr.read_basis_nucleus_index(test_file2, dim=nucleus_num, dtype=np.int32)
+rindices_np_32 = trexio.read_basis_nucleus_index(test_file2, dim=nucleus_num, dtype=np.int32)
 assert rindices_np_32.dtype is np.dtype(np.int32)
 for i in range(nucleus_num):
     assert rindices_np_32[i]==indices_np[i]
 
-rindices_np_64 = tr.read_basis_nucleus_index(test_file2)
+rindices_np_64 = trexio.read_basis_nucleus_index(test_file2)
 assert rindices_np_64.dtype is np.dtype(np.int64)
 assert rindices_np_64.size==nucleus_num
 for i in range(nucleus_num):
     assert rindices_np_64[i]==indices_np[i]
 
 # read nuclear coordinates without providing optional argument dim
-rcoords_np = tr.read_nucleus_coord(test_file2)
+rcoords_np = trexio.read_nucleus_coord(test_file2)
 
 assert rcoords_np.size==nucleus_num*3
 np.testing.assert_array_almost_equal(rcoords_np, np.array(coords).reshape(nucleus_num,3), decimal=8)
 
 # set doReshape to False to get a flat 1D array (e.g. when reading matrices like nuclear coordinates)
-#rcoords_reshaped_2 = tr.read_nucleus_coord(test_file2, doReshape=False)
+#rcoords_reshaped_2 = trexio.read_nucleus_coord(test_file2, doReshape=False)
 
 # read array of nuclear labels
-rlabels_2d = tr.read_nucleus_label(test_file2, dim=nucleus_num)
+rlabels_2d = trexio.read_nucleus_label(test_file2, dim=nucleus_num)
 print(rlabels_2d)
 for i in range(nucleus_num):
     assert rlabels_2d[i]==labels[i]
 
 # read a string corresponding to nuclear point group
-rpoint_group = tr.read_nucleus_point_group(test_file2)
+rpoint_group = trexio.read_nucleus_point_group(test_file2)
 assert rpoint_group==point_group 
 
 # close TREXIO file
-#tr.close(test_file2)
+#trexio.close(test_file2)
 
 # cleaning (remove the TREXIO file)
 try:
-    if TEST_TREXIO_BACKEND == tr.TREXIO_HDF5:
+    if TEST_TREXIO_BACKEND == trexio.TREXIO_HDF5:
         os.remove(output_filename)
-    elif TEST_TREXIO_BACKEND == tr.TREXIO_TEXT:
+    elif TEST_TREXIO_BACKEND == trexio.TREXIO_TEXT:
         shutil.rmtree(output_filename)
 except:
     print (f'No output file {output_filename} has been produced')
diff --git a/python/test/test_pytrexio.py b/python/test/test_pytrexio.py
index b048bfe..04b1266 100644
--- a/python/test/test_pytrexio.py
+++ b/python/test/test_pytrexio.py
@@ -113,7 +113,7 @@ np.testing.assert_array_almost_equal(rcharges_np, charges_np, decimal=8)
 # unsafe call to read_safe should not only have return code = TREXIO_UNSAFE_ARRAY_DIM
 # TODO: it should not return numpy array filled with garbage
 rc, rcharges_fail = trexio_read_safe_nucleus_charge(test_file2, nucleus_num*5)
-assert rc==TREXIO_UNSAFE_ARRAY_DIM
+assert rc==23
 
 # less Python-ic way to read/write arrays using Array classes (probably more portable to other languages)
 #charges2 = doubleArray(nucleus_num)