Add tests for (named) bitstring to suite_asn1write
diff --git a/tests/suites/test_suite_asn1write.function b/tests/suites/test_suite_asn1write.function
index 57a9741..e45583c 100644
--- a/tests/suites/test_suite_asn1write.function
+++ b/tests/suites/test_suite_asn1write.function
@@ -128,3 +128,47 @@
     }
 }
 /* END_CASE */
+
+/* BEGIN_CASE */
+void test_asn1_write_bitstrings( data_t *bitstring, int bits,
+                                 data_t *expected_asn1, int result,
+                                 int is_named )
+{
+    int ret;
+    size_t i;
+    unsigned char buf[150];
+    unsigned char *p;
+
+    memset( buf, GUARD_VAL, sizeof( buf ) );
+
+    p = buf + GUARD_LEN + expected_asn1->len;
+
+    if ( is_named == 0 )
+    {
+        ret = mbedtls_asn1_write_bitstring( &p,
+                                            buf,
+                                            (unsigned char *)bitstring->x,
+                                            (size_t) bits );
+    }
+    else
+    {
+        ret = mbedtls_asn1_write_named_bitstring( &p,
+                                                  buf,
+                                                  (unsigned char *)bitstring->x,
+                                                  (size_t) bits );
+    }
+    TEST_ASSERT( ret == result );
+
+    /* Check for buffer overwrite on both sides */
+    for( i = 0; i < GUARD_LEN; i++ )
+    {
+        TEST_ASSERT( buf[i] == GUARD_VAL );
+        TEST_ASSERT( buf[GUARD_LEN + expected_asn1->len + i] == GUARD_VAL );
+    }
+
+    if ( result >= 0 )
+    {
+        TEST_ASSERT( memcmp( p, expected_asn1->x, expected_asn1->len ) == 0 );
+    }
+}
+/* END_CASE */