test(thin_out): Make thin_out test a controlled RNG test

Fixes issue #4, deals with part of issue #2.

LidarAug/cpp/test/test.cpp

@@ -113,21 +113,6 @@ TEST(DrawUniformValuesTest, BasicAssertions) {
   }
 }
 
-TEST(ThinOutTest, BasicAssertions) {
-  auto points = torch::rand({2, 10, 4});
-  dimensions dims_original = {points.size(0), points.size(1), points.size(2)};
-  auto new_points = thin_out(points, 1);
-  dimensions dims_edited = {new_points.size(0), new_points.size(1),
-                            new_points.size(2)};
-
-  EXPECT_EQ(dims_edited.batch_size, dims_original.batch_size);
-  EXPECT_LT(dims_edited.num_items, dims_original.num_items)
-      << "Expected the amounts to have reduced...\noriginal:\n"
-      << points << "\nnew:\n"
-      << new_points;
-  EXPECT_EQ(dims_edited.num_features, dims_original.num_features);
-}
-
 TEST(RandomNoiseTest, BasicAssertions) {
   auto points =
       torch::tensor({{{1.0, 2.0, 3.0, 10.9}, {4.0, 5.0, 6.0, -10.0}}});
@@ -499,6 +484,37 @@ TEST(RotateRandomTest, BasicAssertions) {
       << "\nexpected_labels:\n"
       << expected_labels;
 }
+
+TEST(ThinOutTest, BasicAssertions) {
+  constexpr tensor_size_t BATCHES = 2;
+  constexpr tensor_size_t ITEMS = 10;
+
+  const auto points = torch::rand({BATCHES, ITEMS, 4}, torch::kF32);
+  auto new_points = thin_out(points, 1);
+
+  // NOTE(tom): percent = 0.653750002, indices = {9, 4, 8, 0}
+  const auto indices = torch::tensor({9, 4, 8, 0});
+
+  const auto expected_points = points.index_select(1, indices);
+
+  EXPECT_EQ(BATCHES, points.size(0)) << "`points` was not supposed to change!";
+  EXPECT_EQ(ITEMS, points.size(1)) << "`points` was not supposed to change!";
+
+  EXPECT_EQ(BATCHES, expected_points.size(0))
+      << "Batch dimensions were not supposed to change!";
+  EXPECT_EQ(BATCHES, new_points.size(0))
+      << "Batch dimensions were not supposed to change!";
+
+  EXPECT_EQ(new_points.size(1), expected_points.size(1))
+      << "Number of points does not match!";
+
+  EXPECT_TRUE(new_points.equal(expected_points))
+      << "Thin out not as expected:\noriginal:\n"
+      << points << "\nexpected:\n"
+      << expected_points << "\nactual:\n"
+      << new_points;
+}
+
 #endif
 
 // NOLINTEND