Add a unit test for combining the edges

tests/CMakeLists.txt

@@ -2,7 +2,7 @@ cmake_policy(SET CMP0054 NEW)
 find_package(GTest REQUIRED)
 include(GoogleTest)
 
-set(SOURCES axis.cpp)
+set(SOURCES axis.cpp triangles.cpp)
 add_executable(axis ${SOURCES})
 
 target_include_directories(

tests/triangles.cpp

@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Copyright (c) 2024 Team Dissolve and contributors
+
+#include "triangle.h"
+#include <gtest/gtest.h>
+#include <numeric>
+
+namespace UnitTest
+{
+
+TEST(TriangleTest, Combine)
+{
+    std::vector<Triangle> ts = {{{-1, 5, 9}, {4, 8, 3}, {-7, 2, 6}}, {{1, -2, -3}, {-4, -8, -6}, {7, -5, -9}}};
+
+    std::vector<Edge> boxes(ts.size());
+    std::transform(ts.begin(), ts.end(), boxes.begin(), [](const auto x) { return x.bounds(); });
+    EXPECT_EQ(boxes[1].start.x, -4);
+    EXPECT_EQ(boxes[1].start.y, -8);
+    EXPECT_EQ(boxes[1].start.z, -9);
+    EXPECT_EQ(boxes[1].end.x, 7);
+    EXPECT_EQ(boxes[1].end.y, -2);
+    EXPECT_EQ(boxes[1].end.z, -3);
+
+    EXPECT_EQ(boxes[0].start.x, -7);
+    EXPECT_EQ(boxes[0].start.y, 2);
+    EXPECT_EQ(boxes[0].start.z, 3);
+    EXPECT_EQ(boxes[0].end.x, 4);
+    EXPECT_EQ(boxes[0].end.y, 8);
+    EXPECT_EQ(boxes[0].end.z, 9);
+
+    auto bounds = std::reduce(boxes.begin(), boxes.end(), boxes[0], [](const auto a, const auto b) { return a.combine(b); });
+
+    EXPECT_EQ(bounds.start.x, -7);
+    EXPECT_EQ(bounds.start.y, -8);
+    EXPECT_EQ(bounds.start.z, -9);
+    EXPECT_EQ(bounds.end.x, 7);
+    EXPECT_EQ(bounds.end.y, 8);
+    EXPECT_EQ(bounds.end.z, 9);
+}
+} // namespace UnitTest