[ble_device_base] Scan-mode request contract on BLEHub (#18061)

tests/components/ble_device_base/test_scan_mode_request.cpp

@@ -0,0 +1,59 @@
+#include <gtest/gtest.h>
+
+#include <cstdint>
+
+#include "esphome/components/ble_device_base/ble_hub.h"
+
+namespace esphome::ble_device_base::testing {
+
+// Pins the request_scan_mode() contract: the base default refuses (so hubs
+// without a mode switch — and out-of-tree trackers — keep building and
+// callers report the real state), while an overriding hub both honors the
+// request and applies it.
+namespace {
+
+class DefaultHub : public BLEHub {
+ public:
+  void register_listener(ESPBTDeviceListener *listener) override {}
+  void set_raw_advertisement_callback(RawAdvertisementCallback callback) override {}
+  HubCapabilities get_capabilities() const override { return {false, false, false}; }
+  void get_adapter_mac(uint8_t out[6]) override {}
+  bool scan_running() override { return false; }
+  // Backed by real state so "changes nothing" is observable: a base default
+  // that silently mutated the hub would flip this and fail the assertion.
+  bool scan_active() override { return this->active_; }
+
+ protected:
+  bool active_{true};
+};
+
+class SwitchingHub : public DefaultHub {
+ public:
+  HubCapabilities get_capabilities() const override { return {true, false, false}; }
+  bool request_scan_mode(bool active) override {
+    this->active_ = active;
+    return true;
+  }
+};
+
+}  // namespace
+
+TEST(BLEHubScanModeRequest, DefaultRefusesAndChangesNothing) {
+  DefaultHub hub;
+  EXPECT_TRUE(hub.scan_active());
+  EXPECT_FALSE(hub.request_scan_mode(false));
+  // Refused, not applied-and-reported-false: the state is untouched.
+  EXPECT_TRUE(hub.scan_active());
+  EXPECT_FALSE(hub.request_scan_mode(true));
+  EXPECT_TRUE(hub.scan_active());
+}
+
+TEST(BLEHubScanModeRequest, OverrideHonorsAndApplies) {
+  SwitchingHub hub;
+  EXPECT_TRUE(hub.request_scan_mode(true));
+  EXPECT_TRUE(hub.scan_active());
+  EXPECT_TRUE(hub.request_scan_mode(false));
+  EXPECT_FALSE(hub.scan_active());
+}
+
+}  // namespace esphome::ble_device_base::testing