🚨 fix C4100 warnings

test/src/unit-udt.cpp

@@ -809,10 +809,6 @@ TEST_CASE("an incomplete type does not trigger a compiler error in non-evaluated
     static_assert(!is_constructible_patched<json, incomplete>::value, "");
 }
 
-// the code below warns about t in MSVC 2015 - this could be a bug
-DOCTEST_MSVC_SUPPRESS_WARNING_PUSH
-DOCTEST_MSVC_SUPPRESS_WARNING(4100)
-
 namespace
 {
 class Evil
@@ -820,13 +816,14 @@ class Evil
   public:
     Evil() = default;
     template <typename T>
-    Evil(T t) : m_i(sizeof(t)) {}
+    Evil(T t) : m_i(sizeof(t))
+    {
+        static_cast<void>(t); // fix MSVC's C4100 warning
+    }
 
     int m_i = 0;
 };
 
-DOCTEST_MSVC_SUPPRESS_WARNING_POP
-
 void from_json(const json& /*unused*/, Evil& /*unused*/) {}
 } // namespace