Problem: no tests for socket_t ctor accepting enum socket_type

Solution: added test case

.travis.yml

@@ -31,6 +31,15 @@ matrix:
         # - llvm-toolchain-trusty-5.0
       # packages:
         # - clang-5.0
+    - os: linux
+      addons:
+        apt:
+          sources:
+            - ubuntu-toolchain-r-test
+          packages:
+            - g++-7
+      env:
+        - MATRIX_EVAL="CC=gcc-7 && CXX=g++-7" BUILD_TYPE=cmake ZMQ_VERSION=4.2.5
 
 sudo: required
 
@@ -39,6 +48,7 @@ before_install:
   
 # Build and check this project according to the BUILD_TYPE
 script:     
+  - eval "${MATRIX_EVAL}"
   - ./ci_build.sh
 
 after_success:

tests/socket.cpp

@@ -7,3 +7,10 @@ TEST(socket, create_destroy)
     zmq::socket_t socket(context, ZMQ_ROUTER);
 }
 
+#ifdef ZMQ_CPP11
+TEST(socket, create_by_enum_destroy)
+{
+    zmq::context_t context;
+    zmq::socket_t socket(context, zmq::socket_type::router);
+}
+#endif