json_formatter: Add tests for formatter::write

Adds some unit tests for the various `formatter::write` overloads.

tests/unit/json_formatter_test.cc

@@ -91,18 +91,15 @@ SEASTAR_TEST_CASE(test_jsonable) {
     return make_ready_future();
 }
 
-SEASTAR_THREAD_TEST_CASE(test_stream_range_as_array) {
+template<typename F>
+void formatter_check_expected(sstring expected, F f, bool close = true) {
     auto vec = std::vector<net::packet>{};
     auto out = output_stream<char>(data_sink(std::make_unique<vector_data_sink>(vec)), 8);
 
-    auto mapper = stream_range_as_array(std::vector<int>{1,2,3}, [] (auto i) {
-        object_json obj;
-        obj.subject = std::to_string(i);
-        obj.values.push(i);
-        return obj;
-    });
-
-    mapper(std::move(out)).get();
+    f(out);
+    if (close) {
+        out.close().get();
+    };
 
     auto packets = net::packet{};
     for (auto &p : vec) {
@@ -112,6 +109,53 @@ SEASTAR_THREAD_TEST_CASE(test_stream_range_as_array) {
     auto buf = packets.release();
 
     sstring result(buf.front().get(), buf.front().size());
-    sstring expected = "[{\"subject\":\"1\",\"values\":[1]}, {\"subject\":\"2\",\"values\":[2]}, {\"subject\":\"3\",\"values\":[3]}]";
     BOOST_CHECK_EQUAL(expected, result);
 }
+
+
+SEASTAR_THREAD_TEST_CASE(test_stream_range_as_array) {
+    sstring expected = "[{\"subject\":\"1\",\"values\":[1]}, {\"subject\":\"2\",\"values\":[2]}, {\"subject\":\"3\",\"values\":[3]}]";
+    formatter_check_expected(expected, [] (auto& out) {
+        auto mapper = stream_range_as_array(std::vector<int>{1,2,3}, [] (auto i) {
+            object_json obj;
+            obj.subject = std::to_string(i);
+            obj.values.push(i);
+            return obj;
+        });
+
+        mapper(std::move(out)).get();
+    }, false);
+}
+
+SEASTAR_THREAD_TEST_CASE(formatter_write) {
+
+    formatter_check_expected("3", [](auto &out) {
+        json::formatter::write(out, 3).get();
+    });
+    formatter_check_expected("false", [](auto &out) {
+        json::formatter::write(out, false).get();
+    });
+    formatter_check_expected("\"foo\"", [](auto &out) {
+        json::formatter::write(out, "foo").get();
+    });
+
+    formatter_check_expected("{1:2,3:4}", [] (auto& out) {
+        json::formatter::write(out, std::map<int, int>({{1, 2}, {3, 4}})).get();
+    });
+    formatter_check_expected("{3:4,1:2}", [] (auto& out) {
+        json::formatter::write(out, std::unordered_map<int, int>({{1, 2}, {3, 4}})).get();
+    });
+    formatter_check_expected("[1,2,3,4]", [](auto &out) {
+        json::formatter::write(out, std::vector<int>({1, 2, 3, 4})).get();
+    });
+
+    formatter_check_expected("[{1:2},{3:4}]", [](auto &out) {
+        json::formatter::write(out, std::vector<std::pair<int, int>>({{1, 2}, {3, 4}})).get();
+    });
+    formatter_check_expected("[{1:2},{3:4}]", [](auto &out) {
+        json::formatter::write(out, std::vector<std::map<int, int>>({{{1, 2}}, {{3, 4}}})).get();
+    });
+    formatter_check_expected("[[1,2],[3,4]]", [](auto &out) {
+        json::formatter::write(out, std::vector<std::vector<int>>({{1, 2}, {3, 4}})).get();
+    });
+}