feat: test for mutex (make this better)

engine/tests/src/thread.cc

@@ -1,5 +1,8 @@
 #include "fishbone/thread.h"
 #include <catch2/catch_test_macros.hpp>
+#include <cstdio>
+#include <cstdlib>
+#include <unistd.h>
 
 struct thread_arg {
     int& a;
@@ -30,4 +33,27 @@ TEST_CASE("Thread") {
 
     th.join();
     REQUIRE(a == 100);
+}
+
+TEST_CASE("Mutex") {
+    for (int i = 0; i < 100; i++) {
+        int a = 0;
+        fishbone::Mutex m;
+
+        fishbone::Thread::CallableFunc func = [&a, &m](auto) {
+            m.lock();
+            for (int j = 0; j < 2; j++) {
+                int b = a;
+                usleep((60 * rand()) / RAND_MAX);
+                a = ++b;
+            }
+            m.unlock();
+        };
+
+        fishbone::Thread th1(func), th2(func);
+
+        th1.join();
+        th2.join();
+        REQUIRE(a == 4);
+    }
 }