Move asn1_skip_integer to the asn1_helpers module

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/include/test/asn1_helpers.h b/tests/include/test/asn1_helpers.h
index ddcc0c9..91ae260 100644
--- a/tests/include/test/asn1_helpers.h
+++ b/tests/include/test/asn1_helpers.h
@@ -22,5 +22,29 @@
 
 #include "test/helpers.h"
 
+/** Skip past an INTEGER in an ASN.1 buffer.
+ *
+ * Mark the current test case as failed in any of the following conditions:
+ * - The buffer does not start with an ASN.1 INTEGER.
+ * - The integer's size or parity does not match the constraints expressed
+ *   through \p min_bits, \p max_bits and \p must_be_odd.
+ *
+ * \param p             Upon entry, `*p` points to the first byte of the
+ *                      buffer to parse.
+ *                      On successful return, `*p` points to the first byte
+ *                      after the parsed INTEGER.
+ *                      On failure, `*p` is unspecified.
+ * \param end           The end of the ASN.1 buffer.
+ * \param min_bits      Fail the test case if the integer does not have at
+ *                      least this many significant bits.
+ * \param max_bits      Fail the test case if the integer has more than
+ *                      this many significant bits.
+ * \param must_be_odd   Fail the test case if the integer is even.
+ *
+ * \return              \c 0 if the test failed, otherwise 1.
+ */
+int mbedtls_test_asn1_skip_integer( unsigned char **p, const unsigned char *end,
+                                    size_t min_bits, size_t max_bits,
+                                    int must_be_odd );
 
 #endif /* ASN1_HELPERS_H */