test: add tests for chunk load/unload radius streaming

tests/testStreaming.cpp

@@ -0,0 +1,70 @@
+#include "testHarness.h"
+#include "vf/Streaming.h"
+
+#include <algorithm>
+
+using namespace vf;
+
+namespace {
+
+long long dist2(ColumnCoord a, ColumnCoord b) {
+    long long dx = a.x - b.x, dz = a.z - b.z;
+    return dx * dx + dz * dz;
+}
+
+bool listContains(const std::vector<ColumnCoord>& list, ColumnCoord column) {
+    return std::find(list.begin(), list.end(), column) != list.end();
+}
+
+} // namespace
+
+VF_TEST(streamRadiusIsDiscSortedNearestFirst) {
+    auto columns = columnsInRadius({0, 0}, 4);
+    CHECK(!columns.empty());
+    CHECK(columns.front() == (ColumnCoord{0, 0}));
+    for (ColumnCoord c : columns) CHECK(dist2(c, {0, 0}) <= 16);
+    CHECK(!listContains(columns, {3, 3}));   // 18 > 16, outside the disc
+    for (std::size_t i = 1; i < columns.size(); ++i)
+        CHECK(dist2(columns[i - 1], {0, 0}) <= dist2(columns[i], {0, 0}));
+}
+
+VF_TEST(streamInitialUpdateLoadsWholeDisc) {
+    ChunkStreamer streamer({4, 6});
+    StreamDelta delta = streamer.update({0, 0});
+    CHECK_EQ(delta.load.size(), columnsInRadius({0, 0}, 4).size());
+    CHECK(delta.unload.empty());
+    CHECK_EQ(streamer.loadedCount(), delta.load.size());
+    CHECK(delta.load.front() == (ColumnCoord{0, 0}));
+    for (std::size_t i = 1; i < delta.load.size(); ++i)
+        CHECK(dist2(delta.load[i - 1], {0, 0}) <= dist2(delta.load[i], {0, 0}));
+}
+
+VF_TEST(streamRepeatedUpdateIsIdempotent) {
+    ChunkStreamer streamer({4, 6});
+    streamer.update({0, 0});
+    StreamDelta again = streamer.update({0, 0});
+    CHECK(again.load.empty());
+    CHECK(again.unload.empty());
+}
+
+VF_TEST(streamStepKeepsOverlapResident) {
+    ChunkStreamer streamer({4, 6});
+    streamer.update({0, 0});
+    StreamDelta delta = streamer.update({1, 0});
+    CHECK(streamer.isLoaded({0, 0}));            // still inside both rings
+    CHECK(!listContains(delta.load, ColumnCoord{0, 0}));   // not reloaded
+    CHECK(!listContains(delta.unload, ColumnCoord{0, 0}));
+}
+
+VF_TEST(streamHysteresisAvoidsThrash) {
+    ChunkStreamer streamer({4, 6});
+    streamer.update({0, 0});
+    streamer.update({5, 0});
+    // (0,0) is distance 5: past the load radius (4) but within the unload
+    // radius (6), so it must stay resident rather than thrash out.
+    CHECK(streamer.isLoaded({0, 0}));
+
+    StreamDelta far = streamer.update({20, 0});
+    CHECK(!streamer.isLoaded({0, 0}));           // now well past the unload ring
+    CHECK(listContains(far.unload, ColumnCoord{0, 0}));
+}