this one is for you Nuno

- pull request might have new bugs given that build is broken.
- this test doesn't expose race conditions under simple tests, yet. It is a starting point.
- run under cuzz (app-verifier) should expose races, this is what it was made for.

src/test/scoped_timer.cpp

@@ -1,9 +1,51 @@
 // test driver for scoped timer.
 // fixes are required to be fuzzed
 // with single and multi-threaded mode and short timeouts.
+// run it with app-verifier (becuzz yes ...)
 
 #include "util/scoped_timer.h"
+#include "util/util.h"
+#include "util/vector.h"
+#include "util/trace.h"
+#include <thread>
+
+class test_scoped_eh : public event_handler {
+    std::atomic<bool> m_called = false;
+public:
+    void operator()(event_handler_caller_t id) override {
+        m_caller_id = id;
+        m_called = true;
+    }
+    bool called() const { return m_called; }
+};
+
+static void worker_thread(unsigned tid) {
+    for (unsigned i = 0; i < 100; ++i) {
+        test_scoped_eh eh;
+        scoped_timer sc(1, &eh);
+        unsigned_vector v;
+        for (unsigned j = 0; j < (2 << 25); ++j) {
+            v.push_back(j);
+            if (eh.called()) {
+                // IF_VERBOSE(0, verbose_stream() << tid << " " << i << " " << j << "\n");
+                break;
+            }
+        }
+    }
+}
 
 void tst_scoped_timer() {
+
+    std::cout << "sequential test\n";
+    worker_thread(0);
+
+    std::cout << "thread test\n";
+    unsigned num_threads = 3;
+    vector<std::thread> threads(num_threads);
+    for (unsigned i = 0; i < num_threads; ++i) 
+        threads[i] = std::thread([&, i]() { worker_thread(i); });
+    
+    for (auto& th : threads) 
+        th.join();
     
 }