[rp2040_ble] Add controller scan primitives (#18001)

tests/components/core/test_event_pool.cpp

@@ -0,0 +1,73 @@
+#include "esphome/core/event_pool.h"
+
+#include <gtest/gtest.h>
+
+#include <set>
+
+namespace esphome::core::testing {
+
+struct PoolItem {
+  int value{0};
+  // EventPool contract: release() cleans up per-object state; nothing here.
+  void release() {}
+};
+
+TEST(EventPool, AllocateUpToCapacityThenNull) {
+  esphome::EventPool<PoolItem, 4> pool;
+  PoolItem *items[4];
+  for (auto *&item : items) {
+    item = pool.allocate();
+    ASSERT_NE(item, nullptr);
+  }
+  // At capacity: the pool refuses rather than growing past SIZE.
+  EXPECT_EQ(pool.allocate(), nullptr);
+}
+
+TEST(EventPool, FullDrainRetainsEveryObject) {
+  // Pins the SIZE + 1 free-list sizing: a fully returned pool must hold all
+  // SIZE objects. With a SIZE-slot ring (capacity SIZE - 1) the last release()
+  // of a full drain was dropped, permanently orphaning one object.
+  esphome::EventPool<PoolItem, 4> pool;
+  PoolItem *items[4];
+  for (auto *&item : items)
+    item = pool.allocate();
+  for (auto *item : items)
+    pool.release(item);
+
+  // Every object must be allocatable again — no orphan, no new creation
+  // (total_created_ is already at SIZE, so a lost object would surface as a
+  // nullptr on the fourth allocation).
+  std::set<PoolItem *> seen;
+  for (int i = 0; i < 4; i++) {
+    PoolItem *item = pool.allocate();
+    ASSERT_NE(item, nullptr);
+    seen.insert(item);
+  }
+  // And they are the same four objects, recycled rather than re-created.
+  for (auto *item : items)
+    EXPECT_TRUE(seen.count(item) == 1);
+  EXPECT_EQ(pool.allocate(), nullptr);
+}
+
+TEST(EventPool, RepeatedDrainCyclesAreStable) {
+  esphome::EventPool<PoolItem, 3> pool;
+  // Several full allocate/release cycles: capacity must not shrink over time.
+  for (int cycle = 0; cycle < 10; cycle++) {
+    PoolItem *items[3];
+    for (auto *&item : items) {
+      item = pool.allocate();
+      ASSERT_NE(item, nullptr);
+    }
+    EXPECT_EQ(pool.allocate(), nullptr);
+    for (auto *item : items)
+      pool.release(item);
+  }
+}
+
+TEST(EventPool, ReleaseNullptrIsSafe) {
+  esphome::EventPool<PoolItem, 2> pool;
+  pool.release(nullptr);
+  EXPECT_NE(pool.allocate(), nullptr);
+}
+
+}  // namespace esphome::core::testing