adding unit test

tests/unit_threadpool.cpp

@@ -0,0 +1,24 @@
+#include <iostream>
+#include <future>
+
+#include "daggy/ThreadPool.hpp"
+
+#include "catch.hpp"
+
+using namespace daggy;
+
+TEST_CASE("Threadpool Construction", "[threadpool]") {
+  std::atomic<uint32_t> cnt(0);
+  ThreadPool tp(10);
+
+  std::vector<std::future<void>> res;
+  for (size_t i = 0; i < 100; ++i) {
+    res.push_back(tp.addTask([&cnt]() -> void { cnt++; return; }));
+  }
+
+  for (auto & r : res) {
+    r.get();
+  }
+
+  REQUIRE(cnt == 100);
+}