Add tests for BN_rand and BN_rand_range

tests/hazmat/backends/test_openssl.py

@@ -169,6 +169,32 @@ def test_bn_to_int(self):
         bn = backend._int_to_bn(0)
         assert backend._bn_to_int(bn) == 0
 
+    def test_bn_rand(self):
+        size_bits = 8
+        rand_bn_ptr = backend._lib.BN_new()
+        assert rand_bn_ptr != backend._ffi.NULL
+        rand_bn_ptr = backend._ffi.gc(rand_bn_ptr, backend._lib.BN_free)
+
+        res = backend._lib.BN_rand(rand_bn_ptr, size_bits, -1, 0)
+        assert res == 1
+
+        # Value should fit in one byte when serialized
+        rand_val = backend._bn_to_int(rand_bn_ptr)
+        int.to_bytes(rand_val, 1, 'big')
+
+    def test_bn_rand_range(self):
+        value = 100
+        bn_range_ptr = backend._int_to_bn(value)
+
+        bn_rand_ptr = backend._lib.BN_new()
+        assert bn_rand_ptr != backend._ffi.NULL
+        bn_rand_ptr = backend._ffi.gc(bn_rand_ptr, backend._lib.BN_free)
+
+        res = backend._lib.BN_rand_range(bn_rand_ptr, bn_range_ptr)
+        assert res == 1
+
+        rand_val = backend._bn_to_int(rand_bn_ptr)
+        assert rand_val < value and rand_val >= 0
 
 class TestOpenSSLRandomEngine(object):
     def setup(self):