Replace rand() with fixed-seed RNG to make tests deterministic

Author: alienx5499

test/libp2p/crypto/marshaller_test.cpp

@@ -11,6 +11,7 @@
 #include <libp2p/crypto/common.hpp>
 #include <libp2p/crypto/protobuf/protobuf_key.hpp>
 #include "mock/libp2p/crypto/key_validator_mock.hpp"
+#include "testutil/libp2p/random.hpp"
 
 using Buffer = std::vector<uint8_t>;
 using libp2p::crypto::Key;
@@ -34,9 +35,7 @@ struct KeyCase {
 };
 
 Buffer randomBuffer(size_t size) {
-  Buffer buf(size, 0);
-  std::generate_n(buf.begin(), size, []() { return rand() & 0xff; });
-  return buf;
+  return testutil::randomBytes(size);
 }
 
 class Pubkey : public testing::TestWithParam<KeyCase<PublicKey>> {

test/libp2p/transport/tcp/tcp_integration_test.cpp

@@ -18,6 +18,7 @@
 #include "mock/libp2p/transport/upgrader_mock.hpp"
 #include "testutil/gmock_actions.hpp"
 #include "testutil/libp2p/peer.hpp"
+#include "testutil/libp2p/random.hpp"
 #include "testutil/prepare_loggers.hpp"
 
 using namespace libp2p::transport;
@@ -175,10 +176,7 @@ TEST(TCP, SingleListenerCanAcceptManyClients) {
         auto conn = expectConnectionValid(rconn);
 
         auto readback = std::make_shared<Bytes>(kSize, 0);
-        auto buf = std::make_shared<Bytes>(kSize, 0);
-        std::generate(buf->begin(), buf->end(), []() {
-          return rand();  // NOLINT
-        });
+        auto buf = std::make_shared<Bytes>(testutil::randomBytes(kSize));
 
         EXPECT_TRUE(conn->isInitiator());
 
@@ -335,10 +333,7 @@ TEST(TCP, OneTransportServerHandlesManyClients) {
         auto conn = expectConnectionValid(rconn);
 
         auto readback = std::make_shared<Bytes>(kSize, 0);
-        auto buf = std::make_shared<Bytes>(kSize, 0);
-        std::generate(buf->begin(), buf->end(), []() {
-          return rand();  // NOLINT
-        });
+        auto buf = std::make_shared<Bytes>(testutil::randomBytes(kSize));
 
         EXPECT_TRUE(conn->isInitiator());
 

test/testutil/libp2p/peer.cpp

@@ -5,14 +5,12 @@
  */
 
 #include <testutil/libp2p/peer.hpp>
+#include <testutil/libp2p/random.hpp>
 
 namespace testutil {
 
   PeerId randomPeerId() {
-    std::vector<uint8_t> rand_key(32, 0);
-    for (auto i = 0u; i < 32u; i++) {
-      rand_key[i] = (rand() & 0xffu);  // NOLINT
-    }
+    auto rand_key = randomBytes(32);
     return PeerId::fromPublicKey(libp2p::crypto::ProtobufKey{rand_key}).value();
   }
 

test/testutil/libp2p/random.hpp

@@ -0,0 +1,40 @@
+/**
+ * Copyright Quadrivium LLC
+ * All Rights Reserved
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <random>
+#include <vector>
+
+namespace testutil {
+
+  /**
+   * Returns a deterministic RNG for tests. Same seed every run for reproducible
+   * tests; avoids flaky behavior from unseeded rand().
+   * NOTE: Shared RNG; test execution order affects the sequence (determinism
+   * is per run, not per test).
+   */
+  inline std::mt19937& getTestRng() {
+    static std::mt19937 rng(0x42);  // arbitrary fixed seed for reproducibility
+    return rng;
+  }
+
+  /**
+   * Fills a buffer with deterministic random bytes. Use in tests instead of
+   * rand() for reproducibility.
+   */
+  inline std::vector<uint8_t> randomBytes(size_t n) {
+    std::vector<uint8_t> buf(n);
+    auto& rng = getTestRng();
+    std::uniform_int_distribution<int> dist(0, 255);
+    for (size_t i = 0; i < n; ++i) {
+      buf[i] = static_cast<uint8_t>(dist(rng));
+    }
+    return buf;
+  }
+
+}  // namespace testutil