From 4553108035b5eb4f82a7dd432bad1b97b97aed11 Mon Sep 17 00:00:00 2001
From: Axel Kohlmeyer <akohlmey@gmail.com>
Date: Tue, 15 Apr 2025 22:11:44 -0400
Subject: [PATCH] add minimal unit test for JSON class

---
 unittest/utils/CMakeLists.txt |  4 ++
 unittest/utils/test_json.cpp  | 77 +++++++++++++++++++++++++++++++++++
 2 files changed, 81 insertions(+)
 create mode 100644 unittest/utils/test_json.cpp

diff --git a/unittest/utils/CMakeLists.txt b/unittest/utils/CMakeLists.txt
index c277a0353b..8c09a1b1c7 100644
--- a/unittest/utils/CMakeLists.txt
+++ b/unittest/utils/CMakeLists.txt
@@ -49,6 +49,10 @@ add_executable(test_fmtlib test_fmtlib.cpp)
 target_link_libraries(test_fmtlib PRIVATE lammps GTest::GMockMain)
 add_test(NAME FmtLib COMMAND test_fmtlib)
 
+add_executable(test_json test_json.cpp)
+target_link_libraries(test_json PRIVATE lammps GTest::GMockMain)
+add_test(NAME JSON COMMAND test_json)
+
 add_executable(test_math_eigen_impl test_math_eigen_impl.cpp)
 target_include_directories(test_math_eigen_impl PRIVATE ${LAMMPS_SOURCE_DIR})
 add_test(NAME MathEigen COMMAND test_math_eigen_impl 10 5)
diff --git a/unittest/utils/test_json.cpp b/unittest/utils/test_json.cpp
new file mode 100644
index 0000000000..e8cab895c3
--- /dev/null
+++ b/unittest/utils/test_json.cpp
@@ -0,0 +1,77 @@
+/* ----------------------------------------------------------------------
+   LAMMPS - Large-scale Atomic/Molecular Massively Parallel Simulator
+   https://www.lammps.org/, Sandia National Laboratories
+   LAMMPS Development team: developers@lammps.org
+
+   Copyright (2003) Sandia Corporation.  Under the terms of Contract
+   DE-AC04-94AL85000 with Sandia Corporation, the U.S. Government retains
+   certain rights in this software.  This software is distributed under
+   the GNU General Public License.
+
+   See the README file in the top-level LAMMPS directory.
+------------------------------------------------------------------------- */
+
+#include "lmptype.h"
+#include "nlohmann/json.hpp"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+#include <exception>
+#include <string>
+
+using namespace LAMMPS_NS;
+using ::testing::Eq;
+using json = ::nlohmann_lmp::json;
+
+#define STRINGIFY(val) XSTR(val)
+#define XSTR(val) #val
+
+// this tests a subset of the JSON class that is most relevant to LAMMPS
+
+TEST(JSON, namespace)
+{
+    std::string expected = "nlohmann_lmp::json_abi";
+    expected += "_v" STRINGIFY(NLOHMANN_JSON_VERSION_MAJOR);
+    expected += "_" STRINGIFY(NLOHMANN_JSON_VERSION_MINOR);
+    expected += "_" STRINGIFY(NLOHMANN_JSON_VERSION_PATCH);
+
+    const std::string ns{STRINGIFY(NLOHMANN_JSON_NAMESPACE)};
+    ASSERT_THAT(expected, Eq(ns));
+}
+
+TEST(JSON, serialize_deserialize)
+{
+    json j1;
+    j1["pi"]      = 3.141;
+    j1["happy"]   = true;
+    j1["name"]    = "Niels";
+    j1["nothing"] = nullptr;
+
+    std::string expected = "{\"happy\":true,\"name\":\"Niels\",\"nothing\":null,\"pi\":3.141}";
+    std::string dumped   = j1.dump();
+    ASSERT_THAT(expected, Eq(dumped));
+
+    json j2 = json::parse(expected);
+    ASSERT_TRUE(j1 == j2);
+}
+
+TEST(JSON, init_vs_incremental)
+{
+    json j1;
+    j1["pi"]                   = 3.141;
+    j1["happy"]                = true;
+    j1["name"]                 = "Niels";
+    j1["nothing"]              = nullptr;
+    j1["answer"]["everything"] = 42;
+    j1["list"]                 = {1, 0, 2};
+    j1["object"]               = {{"currency", "USD"}, {"value", 42.99}};
+
+    json j2 = {{"pi", 3.141},
+               {"happy", true},
+               {"name", "Niels"},
+               {"nothing", nullptr},
+               {"answer", {{"everything", 42}}},
+               {"list", {1, 0, 2}},
+               {"object", {{"currency", "USD"}, {"value", 42.99}}}};
+
+    ASSERT_TRUE(j1 == j2);
+}