test: Revert to random path element

Author: MarcoFalke

src/test/util/setup_common.cpp

@@ -75,6 +75,8 @@ using node::VerifyLoadedChainstate;
 const std::function<std::string(const char*)> G_TRANSLATION_FUN = nullptr;
 
 constexpr inline auto TEST_DIR_PATH_ELEMENT{"test_common bitcoin"}; // Includes a space to catch possible path escape issues.
+/** Random context to get unique temp data dirs. Separate from m_rng, which can be seeded from a const env var */
+static FastRandomContext g_rng_temp_path;
 
 struct NetworkSetup
 {
@@ -138,8 +140,12 @@ BasicTestingSetup::BasicTestingSetup(const ChainType chainType, TestOpts opts)
 
     const std::string test_name{G_TEST_GET_FULL_NAME ? G_TEST_GET_FULL_NAME() : ""};
     if (!m_node.args->IsArgSet("-testdatadir")) {
-        const auto now{TicksSinceEpoch<std::chrono::nanoseconds>(SystemClock::now())};
-        m_path_root = fs::temp_directory_path() / TEST_DIR_PATH_ELEMENT / test_name / util::ToString(now);
+        // To avoid colliding with a leftover prior datadir, and to allow
+        // tests, such as the fuzz tests to run in several processes at the
+        // same time, add a random element to the path. Keep it small enough to
+        // avoid a MAX_PATH violation on Windows.
+        const auto rand{HexStr(g_rng_temp_path.randbytes(10))};
+        m_path_root = fs::temp_directory_path() / TEST_DIR_PATH_ELEMENT / test_name / rand;
         TryCreateDirectories(m_path_root);
     } else {
         // Custom data directory