Use mbedtls_test_read_mpi in test suites

Replace calls to mbedtls_mpi_read_string() with a wrapper
mbedtls_test_read_mpi() when reading test data except for the purpose
of testing mbedtls_mpi_read_string() itself. The wrapper lets the test
data control precisely how many limbs the constructed MPI has.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/suites/test_suite_ecdh.function b/tests/suites/test_suite_ecdh.function
index da0531b..69197e6 100644
--- a/tests/suites/test_suite_ecdh.function
+++ b/tests/suites/test_suite_ecdh.function
@@ -278,21 +278,21 @@
                                           mbedtls_test_rnd_buffer_rand,
                                           &rnd_info_A ) == 0 );
     TEST_ASSERT( ! mbedtls_ecp_is_zero( &qA ) );
-    TEST_ASSERT( mbedtls_mpi_read_string( &check, 16, xA_str ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &check, 16, xA_str ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &qA.X, &check ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_read_string( &check, 16, yA_str ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &check, 16, yA_str ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &qA.Y, &check ) == 0 );
 
     TEST_ASSERT( mbedtls_ecdh_gen_public( &grp, &dB, &qB,
                                           mbedtls_test_rnd_buffer_rand,
                                           &rnd_info_B ) == 0 );
     TEST_ASSERT( ! mbedtls_ecp_is_zero( &qB ) );
-    TEST_ASSERT( mbedtls_mpi_read_string( &check, 16, xB_str ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &check, 16, xB_str ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &qB.X, &check ) == 0 );
-    TEST_ASSERT( mbedtls_mpi_read_string( &check, 16, yB_str ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &check, 16, yB_str ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &qB.Y, &check ) == 0 );
 
-    TEST_ASSERT( mbedtls_mpi_read_string( &check, 16, z_str ) == 0 );
+    TEST_ASSERT( mbedtls_test_read_mpi( &check, 16, z_str ) == 0 );
     TEST_ASSERT( mbedtls_ecdh_compute_shared( &grp, &zA, &qB, &dA, NULL, NULL ) == 0 );
     TEST_ASSERT( mbedtls_mpi_cmp_mpi( &zA, &check ) == 0 );
     TEST_ASSERT( mbedtls_ecdh_compute_shared( &grp, &zB, &qA, &dB, NULL, NULL ) == 0 );