Increased test coverage

extras/tests/JsonVariant/add.cpp

@@ -10,21 +10,37 @@ TEST_CASE("JsonVariant::add()") {
   DynamicJsonDocument doc(4096);
   JsonVariant var = doc.to<JsonVariant>();
 
-  SECTION("integer") {
+  SECTION("add integer to new variant") {
     var.add(42);
 
     REQUIRE(var.as<std::string>() == "[42]");
   }
 
-  SECTION("const char*") {
+  SECTION("add const char* to new variant") {
     var.add("hello");
 
     REQUIRE(var.as<std::string>() == "[\"hello\"]");
   }
 
-  SECTION("std::string") {
+  SECTION("add std::string to new variant") {
     var.add(std::string("hello"));
 
     REQUIRE(var.as<std::string>() == "[\"hello\"]");
   }
+
+  SECTION("add integer to integer") {
+    var.set(123);
+
+    var.add(456);  // no-op
+
+    REQUIRE(var.as<std::string>() == "123");
+  }
+
+  SECTION("add integer to object") {
+    var["val"] = 123;
+
+    var.add(456);  // no-op
+
+    REQUIRE(var.as<std::string>() == "{\"val\":123}");
+  }
 }