Add failing unit test for TopicTree

tests/TopicTree.cpp

@@ -0,0 +1,49 @@
+#include "../src/TopicTree.h"
+
+#include <cassert>
+#include <iostream>
+
+uWS::TopicTree *topicTree;
+
+void testUnsubscribeInside() {
+
+    topicTree = new uWS::TopicTree([](uWS::Subscriber *s, std::string_view data) {
+        std::cout << s << " got <" << data << ">" << std::endl;
+
+        if (s == (void *) UINTPTR_MAX) {
+            std::cout << "Error! Received UINTPTR_MAX as Subscriber!" << std::endl;
+            exit(-1);
+        }
+
+        /* This one causes the following cb to get UINTPTR_MAX */
+        topicTree->unsubscribeAll(s);
+
+        return 0;
+    });
+
+    uWS::Subscriber *s1 = new uWS::Subscriber(nullptr);
+    uWS::Subscriber *s2 = new uWS::Subscriber(nullptr);
+
+    std::cout << "s1 = " << s1 << std::endl;
+    std::cout << "s2 = " << s2 << std::endl;
+
+    topicTree->subscribe("1", s1);
+    topicTree->subscribe("2", s2);
+
+    topicTree->publish("1", "Ett!");
+    topicTree->publish("2", "Två!");
+
+    topicTree->drain();
+
+    topicTree->unsubscribeAll(s1);
+    topicTree->unsubscribeAll(s2);
+
+    delete s1;
+    delete s2;
+
+    delete topicTree;
+}
+
+int main() {
+    testUnsubscribeInside();
+}