restore a subset of the rand module (#708)

* restore a subset of the rand module

* flake

* remove cleanup, go ahead and assume status will always be 1

* lighten and add power
diff --git a/tests/test_rand.py b/tests/test_rand.py
new file mode 100644
index 0000000..e04a24c
--- /dev/null
+++ b/tests/test_rand.py
@@ -0,0 +1,38 @@
+# Copyright (c) Frederick Dean
+# See LICENSE for details.
+
+"""
+Unit tests for `OpenSSL.rand`.
+"""
+
+import pytest
+
+from OpenSSL import rand
+
+
+class TestRand(object):
+
+    @pytest.mark.parametrize('args', [
+        (b"foo", None),
+        (None, 3),
+    ])
+    def test_add_wrong_args(self, args):
+        """
+        `OpenSSL.rand.add` raises `TypeError` if called with arguments not of
+        type `str` and `int`.
+        """
+        with pytest.raises(TypeError):
+            rand.add(*args)
+
+    def test_add(self):
+        """
+        `OpenSSL.rand.add` adds entropy to the PRNG.
+        """
+        rand.add(b'hamburger', 3)
+
+    def test_status(self):
+        """
+        `OpenSSL.rand.status` returns `1` if the PRNG has sufficient entropy,
+        `0` otherwise.
+        """
+        assert rand.status() == 1