From 5a548408843094a05debe1c03545f8030f12690d Mon Sep 17 00:00:00 2001
From: Pascal Leroy <pascal.h.leroy@gmail.com>
Date: Sun, 9 Oct 2022 18:18:48 +0200
Subject: [PATCH] A test.

---
 numerics/nearest_neighbour_test.cpp | 62 ++++++++++++++++++++++++++---
 1 file changed, 56 insertions(+), 6 deletions(-)

diff --git a/numerics/nearest_neighbour_test.cpp b/numerics/nearest_neighbour_test.cpp
index 118d0d4a6b..369df8c4ec 100644
--- a/numerics/nearest_neighbour_test.cpp
+++ b/numerics/nearest_neighbour_test.cpp
@@ -26,11 +26,16 @@ class PrincipalComponentPartitioningTreeTest : public ::testing::Test {
   using V = Vector<double, World>;
 
   // Computes the nearest point using the brute force algorithm.
-  V const* BruteForceNearestNeighbour(V const& query_value,
-                                      std::vector<V> const& values) {
+  V const* BruteForceNearestNeighbour(
+      V const& query_value,
+      std::vector<V> const& values,
+      PrincipalComponentPartitioningTree<V>::Filter const& filter = nullptr) {
     V const* nearest = nullptr;
     double nearest_distance = Infinity<double>;
     for (auto const& value : values) {
+      if (filter != nullptr && !filter(&value)) {
+        continue;
+      }
       double const distance = (value - query_value).Norm();
       if (distance < nearest_distance) {
         nearest_distance = distance;
@@ -142,8 +147,8 @@ TEST_F(PrincipalComponentPartitioningTreeTest, RandomConstructor) {
     auto* const nearest1 = tree1.FindNearestNeighbour(query_point);
     auto* const nearest3 = tree3.FindNearestNeighbour(query_point);
 
-    EXPECT_THAT(nearest1, Eq(nearest));
-    EXPECT_THAT(nearest3, Eq(nearest));
+    EXPECT_THAT(nearest1, Eq(nearest)) << *nearest1 << " " << *nearest;
+    EXPECT_THAT(nearest3, Eq(nearest)) << *nearest3 << " " << *nearest;
   }
 }
 
@@ -181,9 +186,54 @@ TEST_F(PrincipalComponentPartitioningTreeTest, RandomAdd) {
     auto* const nearest1 = tree1.FindNearestNeighbour(query_point);
     auto* const nearest3 = tree3.FindNearestNeighbour(query_point);
 
-    EXPECT_THAT(nearest1, Eq(nearest));
-    EXPECT_THAT(nearest3, Eq(nearest));
+    EXPECT_THAT(nearest1, Eq(nearest)) << *nearest1 << " " << *nearest;
+    EXPECT_THAT(nearest3, Eq(nearest)) << *nearest3 << " " << *nearest;
+  }
+}
+
+// Random points with a filter, validated against the brute force algorithm.
+TEST_F(PrincipalComponentPartitioningTreeTest, RandomFilter) {
+  static constexpr int points_in_tree = 100;
+  static constexpr int points_to_test = 10;
+  std::mt19937_64 random(42);
+  std::uniform_real_distribution<double> coordinate_distribution(-10, 10);
+
+  // Build two trees with the same points but different leaf sizes.
+  std::vector<V> tree_points;
+  std::vector<not_null<V const*>> tree_pointers;
+  MakeValues(points_in_tree,
+             tree_points,
+             tree_pointers,
+             random,
+             coordinate_distribution);
+  PrincipalComponentPartitioningTree<V> tree1(tree_pointers,
+                                              /*max_values_per_cell=*/1);
+  PrincipalComponentPartitioningTree<V> tree3(tree_pointers,
+                                              /*max_values_per_cell=*/3);
+
+  const PrincipalComponentPartitioningTree<V>::Filter filter =
+      [](V const* const point) {
+    return point->Norm²() < 100;
+  };
+
+  bool filtering_was_effective = false;
+  for (int i = 0; i < points_to_test; ++i) {
+    auto const query_point = V({coordinate_distribution(random),
+                                coordinate_distribution(random),
+                                coordinate_distribution(random)});
+
+    auto* const nearest =
+        BruteForceNearestNeighbour(query_point, tree_points, filter);
+    auto* const nearest1 = tree1.FindNearestNeighbour(query_point, filter);
+    auto* const nearest3 = tree3.FindNearestNeighbour(query_point, filter);
+
+    EXPECT_THAT(nearest1, Eq(nearest)) << *nearest1 << " " << *nearest;
+    EXPECT_THAT(nearest3, Eq(nearest)) << *nearest3 << " " << *nearest;
+
+    filtering_was_effective |=
+        nearest != BruteForceNearestNeighbour(query_point, tree_points);
   }
+  EXPECT_TRUE(filtering_was_effective) << "Filtering did nothing";
 }
 
 }  // namespace numerics