Add tests for mbedtls_oid_get_numeric_string()

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/tests/suites/test_suite_oid.function b/tests/suites/test_suite_oid.function
index 687b216..3004b65 100644
--- a/tests/suites/test_suite_oid.function
+++ b/tests/suites/test_suite_oid.function
@@ -96,3 +96,24 @@
     }
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void oid_get_numeric_string(data_t *oid, int error_ret, char *result_str)
+{
+    char buf[256];
+    mbedtls_asn1_buf input_oid = { 0, 0, NULL };
+    int ret;
+
+    input_oid.tag = MBEDTLS_ASN1_OID;
+    input_oid.p = oid->x;
+    input_oid.len = oid->len;
+
+    ret = mbedtls_oid_get_numeric_string(buf, sizeof(buf), &input_oid);
+
+    if (error_ret == 0) {
+        TEST_ASSERT(strcmp(buf, result_str) == 0);
+    } else {
+        TEST_EQUAL(ret, error_ret);
+    }
+}
+/* END_CASE */