diff --git a/tests/test_stl_io.c b/tests/test_stl_io.c
index 185acdb..7a6c70e 100644
--- a/tests/test_stl_io.c
+++ b/tests/test_stl_io.c
@@ -151,7 +151,6 @@ static const char* test_stlb_header_write()
     const char* filepath = "temp/solid.stlb";
     struct gmio_stlb_header header = {0};
     const char* header_str = "temp/solid.stlb generated with gmio library";
-    int error = GMIO_ERROR_OK;
 
     {
         FILE* outfile = fopen(filepath, "wb");
@@ -159,7 +158,7 @@ static const char* test_stlb_header_write()
         memcpy(&header,
                header_str,
                GMIO_MIN(GMIO_STLB_HEADER_SIZE, strlen(header_str)));
-        error = gmio_stlb_header_write(
+        const int error = gmio_stlb_header_write(
                     &stream, GMIO_ENDIANNESS_LITTLE, &header, 0);
         fclose(outfile);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
@@ -168,7 +167,7 @@ static const char* test_stlb_header_write()
     {
         struct gmio_stl_data data = {0};
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(filepath, &creator, NULL);
+        const int error = gmio_stl_read_file(filepath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_ASSERT(gmio_stlb_header_equal(&header, &data.header));
         UTEST_COMPARE_UINT(0, data.tri_array.count);
@@ -192,12 +191,11 @@ static const char* test_stlb_write()
     const char* model_fpath_out = "temp/solid.le_stlb";
     const char* model_fpath_out_be = "temp/solid.be_stlb";
     struct gmio_stl_data data = {0};
-    int error = GMIO_ERROR_OK;
 
     /* Read input model file */
     {
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(model_fpath, &creator, NULL);
+        const int error = gmio_stl_read_file(model_fpath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
@@ -208,13 +206,14 @@ static const char* test_stlb_write()
         const struct gmio_stl_mesh mesh = gmio_stl_data_mesh(&data);
         struct gmio_stl_write_options opts = {0};
         opts.stlb_header = data.header;
-        error = gmio_stl_write_file(
+        int error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_BINARY_LE, model_fpath_out, &mesh, &opts);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
 
         /* Big-endian version */
         error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_BINARY_BE, model_fpath_out_be, &mesh, &opts);
+        UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
     /* Check input and output models are equal */
@@ -251,7 +250,7 @@ static const char* test_stlb_write()
     {
         struct gmio_stl_data data_be = {0};
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data_be);
-        error = gmio_stl_read_file(model_fpath_out_be, &creator, NULL);
+        const int error = gmio_stl_read_file(model_fpath_out_be, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_ASSERT(gmio_stlb_header_equal(&data.header, &data_be.header));
         UTEST_COMPARE_UINT(data.tri_array.count, data_be.tri_array.count);
@@ -273,12 +272,11 @@ static const char* test_stla_write()
     const char* model_filepath_out = "temp/solid.stla";
     struct gmio_stl_data data = {0}; /* TODO: fix memory leak on error */
     char header_str[GMIO_STLB_HEADER_SIZE + 1] = {0};
-    int error = GMIO_ERROR_OK;
 
     /* Read input model file */
     {
         struct gmio_stl_mesh_creator creator = gmio_stl_data_mesh_creator(&data);
-        error = gmio_stl_read_file(model_filepath, &creator, NULL);
+        const int error = gmio_stl_read_file(model_filepath, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
 
@@ -290,7 +288,7 @@ static const char* test_stla_write()
         opts.stla_solid_name = header_str;
         opts.stla_float32_prec = 7;
         opts.stla_float32_format = GMIO_FLOAT_TEXT_FORMAT_SHORTEST_LOWERCASE;
-        error = gmio_stl_write_file(
+        const int error = gmio_stl_write_file(
                     GMIO_STL_FORMAT_ASCII, model_filepath_out, &mesh, &opts);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
     }
@@ -301,18 +299,17 @@ static const char* test_stla_write()
         struct gmio_stl_data data_stla = {0};
         struct gmio_stl_mesh_creator creator =
                 gmio_stl_data_mesh_creator(&data_stla);
-        size_t i = 0;
         gmio_cstr_copy(
                     trim_header_str,
                     sizeof(trim_header_str),
                     header_str,
                     sizeof(header_str));
         gmio_string_trim_from_end(trim_header_str, sizeof(header_str));
-        error = gmio_stl_read_file(model_filepath_out, &creator, NULL);
+        const int error = gmio_stl_read_file(model_filepath_out, &creator, NULL);
         UTEST_COMPARE_INT(GMIO_ERROR_OK, error);
         UTEST_COMPARE_UINT(data.tri_array.count, data_stla.tri_array.count);
         UTEST_COMPARE_CSTR(trim_header_str, data_stla.solid_name);
-        for (i = 0; i < data.tri_array.count; ++i) {
+        for (size_t i = 0; i < data.tri_array.count; ++i) {
             const struct gmio_stl_triangle* lhs = &data.tri_array.ptr[i];
             const struct gmio_stl_triangle* rhs = &data_stla.tri_array.ptr[i];
             const bool tri_equal = gmio_stl_triangle_equal(lhs, rhs, 5);