test: Introduce MockableSteadyClock::mock_time_point and ElapseSteady helper

This refactor clarifies that the MockableSteadyClock::mock_time_point
has millisecond precision by defining a type an using it.

Moreover, a ElapseSteady helper is added which can be re-used easily.

src/test/util/CMakeLists.txt

@@ -15,6 +15,7 @@ add_library(test_util STATIC EXCLUDE_FROM_ALL
   script.cpp
   setup_common.cpp
   str.cpp
+  time.cpp
   transaction_utils.cpp
   txmempool.cpp
   validation.cpp

src/test/util/time.cpp

@@ -0,0 +1,5 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/util/time.h>

src/test/util/time.h

@@ -0,0 +1,23 @@
+// Copyright (c) The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_TEST_UTIL_TIME_H
+#define BITCOIN_TEST_UTIL_TIME_H
+
+#include <util/time.h>
+
+struct ElapseSteady {
+    MockableSteadyClock::mock_time_point::duration t{MockableSteadyClock::INITIAL_MOCK_TIME};
+    ElapseSteady()
+    {
+        (*this)(0s); // init
+    }
+    void operator()(std::chrono::milliseconds d)
+    {
+        t += d;
+        MockableSteadyClock::SetMockTime(t);
+    }
+};
+
+#endif // BITCOIN_TEST_UTIL_TIME_H

src/util/time.cpp

@@ -21,7 +21,7 @@ void UninterruptibleSleep(const std::chrono::microseconds& n) { std::this_thread
 
 static std::atomic<std::chrono::seconds> g_mock_time{}; //!< For testing
 std::atomic<bool> g_used_system_time{false};
-static std::atomic<std::chrono::milliseconds> g_mock_steady_time{}; //!< For testing
+static std::atomic<MockableSteadyClock::mock_time_point::duration> g_mock_steady_time{}; //!< For testing
 
 NodeClock::time_point NodeClock::now() noexcept
 {
@@ -62,7 +62,7 @@ MockableSteadyClock::time_point MockableSteadyClock::now() noexcept
     return time_point{ret};
 };
 
-void MockableSteadyClock::SetMockTime(std::chrono::milliseconds mock_time_in)
+void MockableSteadyClock::SetMockTime(mock_time_point::duration mock_time_in)
 {
     Assert(mock_time_in >= 0s);
     g_mock_steady_time.store(mock_time_in, std::memory_order_relaxed);

src/util/time.h

@@ -38,7 +38,8 @@ using SystemClock = std::chrono::system_clock;
 struct MockableSteadyClock : public std::chrono::steady_clock {
     using time_point = std::chrono::time_point<MockableSteadyClock>;
 
-    static constexpr std::chrono::milliseconds INITIAL_MOCK_TIME{1};
+    using mock_time_point = std::chrono::time_point<MockableSteadyClock, std::chrono::milliseconds>;
+    static constexpr mock_time_point::duration INITIAL_MOCK_TIME{1};
 
     /** Return current system time or mocked time, if set */
     static time_point now() noexcept;
@@ -50,7 +51,7 @@ struct MockableSteadyClock : public std::chrono::steady_clock {
      * for testing.
      * To stop mocking, call ClearMockTime().
      */
-    static void SetMockTime(std::chrono::milliseconds mock_time_in);
+    static void SetMockTime(mock_time_point::duration mock_time_in);
 
     /** Clear mock time, go back to system steady clock. */
     static void ClearMockTime();