obfs, test: Add tests for random

test/impl/random.cpp

@@ -0,0 +1,25 @@
+#include <obfs/random.hpp>
+#include <catch2/catch.hpp>
+
+using uint64_t = unsigned long long;
+
+// https://en.wikipedia.org/wiki/Xorshift
+uint64_t xorshift128plus(uint64_t state[2]) {
+	uint64_t t = state[0];
+	uint64_t const s = state[1];
+	state[0] = s;
+	t ^= t << 23;		// a
+	t ^= t >> 17;		// b
+	t ^= s ^ (s >> 26);	// c
+	state[1] = t;
+	return t + s;
+}
+
+TEST_CASE("Random case", "[obfs::Xorshift+]") {
+    constexpr size_t val = MAKE_RAND_VAL(100);
+    uint64_t state[2] = { val, val << 1 };
+
+    REQUIRE(obfs::Xorshiftplus<val, 1>::value == xorshift128plus(state));
+    REQUIRE(obfs::Xorshiftplus<val, 2>::value == xorshift128plus(state));
+    REQUIRE(obfs::Xorshiftplus<val, 3>::value == xorshift128plus(state));
+}