test homebrew on OSX
diff --git a/.travis.yml b/.travis.yml
index b459f5d..64deb2f 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -168,3 +168,8 @@
   - if [ `which valgrind` ]; then
     valgrind --error-exitcode=1 --leak-check=full ./json_unit ;
     fi
+  - if [ $os = "osx" ]; then
+    brew tap nlohmann/json ;
+    brew install nlohmann_json --HEAD ;
+    brew test nlohmann_json
+    fi