Add checks to guarantee positive input parameters

Signed-off-by: Gabor Mezei <gabor.mezei@arm.com>
diff --git a/tests/suites/test_suite_ecp.function b/tests/suites/test_suite_ecp.function
index 39fdefa..59dcb6f 100644
--- a/tests/suites/test_suite_ecp.function
+++ b/tests/suites/test_suite_ecp.function
@@ -1378,6 +1378,9 @@
     limbs_X = X.n;
     limbs_N = N.n;
     limbs_res = res.n;
+    TEST_ASSERT(mbedtls_mpi_core_uint_le_mpi(0, X.p, X.n));
+    TEST_ASSERT(mbedtls_mpi_core_uint_le_mpi(0, N.p, N.n));
+    TEST_ASSERT(mbedtls_mpi_core_uint_le_mpi(0, res.p, res.n));
 
     size_t limbs = limbs_N;
     size_t bytes = limbs * sizeof(mbedtls_mpi_uint);