adds test for user-defined operator

Author: attwoodn

tests/expression_tree.cpp

@@ -1,5 +1,6 @@
 #include <attwoodn/expression_tree.hpp>
 #include "test_utils.hpp"
+#include <functional>
 #include <cassert>
 
 using namespace attwoodn::expression_tree;
@@ -276,5 +277,48 @@ void test_copied_expression_tree() {
 }
 
 void test_user_defined_operator() {
+    auto is_small_packet_payload = [](const packet_payload& incoming, const packet_payload&) -> bool {
+        if(incoming.error_code == 0 && incoming.checksum_ok && incoming.payload_size() <= 10) {
+            return true;
+        }
+        return false;
+    };
+
+    // only accept small, non-errored data packets from Jim. 
+    // evaluate packet contents using the user-defined lambda operator defined above
+    expression_tree<data_packet> expr {
+        make_expr(&data_packet::sender_name, op::equals, std::string("Jim"))
+        ->AND(make_expr(&data_packet::payload, is_small_packet_payload, packet_payload()))
+    };
+
+    data_packet incoming_packet;
+
+    // Jim sends a small, non-errored data packet
+    incoming_packet.sender_name = "Jim";
+    incoming_packet.payload.checksum_ok = true;
+    incoming_packet.payload.data = "hello!";
+    incoming_packet.payload.error_code = 0;
+    assert(expr.evaluate(incoming_packet));      // passes evaluation
+
+    // Pam sends the same packet payload
+    incoming_packet.sender_name = "Pam";
+    assert(!expr.evaluate(incoming_packet));     // fails evaluation. No messages from Pam are accepted (sorry Pam)
+
+    // Jim sends a packet with a bad checksum
+    incoming_packet.sender_name = "Jim";
+    incoming_packet.payload.checksum_ok = false;
+    assert(!expr.evaluate(incoming_packet));     // fails evaluation. The packet was from Jim, but the checksum was bad
+
+    // Jim sends a packet whose payload is too big
+    incoming_packet.payload.checksum_ok = true;
+    incoming_packet.payload.data = "Boy do I have a long story for you - so I was talking to Pam ...";
+    assert(!expr.evaluate(incoming_packet));     // fails evaluation. The packet's payload was too big. Give me the TLDR next time, Jim
+
+    // Jim sends a small, rude packet
+    incoming_packet.payload.data = "Dwight sux";
+    assert(expr.evaluate(incoming_packet));      // passes evaluation. The packet's payload was the right size this time
 
+    // Jim sends a packet has an error code
+    incoming_packet.payload.error_code = 404;
+    assert(!expr.evaluate(incoming_packet));     // fails evaluation. The packet's payload had an error code
 }

tests/test_utils.hpp

@@ -18,15 +18,17 @@ struct test_fixture {
 };
 
 struct packet_payload {
-    const uint16_t error_code; 
+    uint16_t error_code; 
     std::string data;
+    bool checksum_ok;
 
     uint64_t payload_size() const {
         return data.size();
     }
 };
 
 class data_packet {
-    const uint32_t sender_id;
-    packet_payload payload;
+    public:
+        std::string sender_name;
+        packet_payload payload;
 };