Test file transmission: find free port

test/test_file_transmission.cpp

@@ -45,6 +45,25 @@ TEST(Transmission, FileUpload)
     sa_lsn.sin_addr.s_addr = INADDR_ANY;
     sa_lsn.sin_port = htons(5555);
 
+    // Find unused a port not used by any other service.    
+    // Otherwise srt_connect may actually connect.
+    int bind_res = -1;
+    for (int port = 5000; port <= 5555; ++port)
+    {
+        sa_lsn.sin_port = htons(port);
+        bind_res = srt_bind(sock_lsn, (sockaddr*)&sa_lsn, sizeof sa_lsn);
+        if (bind_res == 0)
+        {
+            std::cout << "Running test on port " << port << "\n";
+            break;
+        }
+
+        ASSERT_TRUE(bind_res == SRT_EINVOP) << "Bind failed not due to an occupied port. Result " << bind_res;
+
+    }
+
+    ASSERT_GE(bind_res, 0);
+
     srt_bind(sock_lsn, (sockaddr*)&sa_lsn, sizeof sa_lsn);
 
     int optval = 0;
@@ -110,7 +129,7 @@ TEST(Transmission, FileUpload)
 
     sockaddr_in sa = sockaddr_in();
     sa.sin_family = AF_INET;
-    sa.sin_port = htons(5555);
+    sa.sin_port = sa_lsn.sin_port;
     ASSERT_EQ(inet_pton(AF_INET, "127.0.0.1", &sa.sin_addr), 1);
 
     srt_connect(sock_clr, (sockaddr*)&sa, sizeof(sa));