diff --git a/esphome/core/__init__.py b/esphome/core/__init__.py
index 484f6793696..a86478aca19 100644
--- a/esphome/core/__init__.py
+++ b/esphome/core/__init__.py
@@ -615,6 +615,10 @@ class EsphomeCore:
         self.address_cache: AddressCache | None = None
         # Cached config hash (computed lazily)
         self._config_hash: int | None = None
+        # True if compiling for C++ unit tests
+        self.cpp_testing = False
+        # Allowlist of components whose to_code should run during C++ testing
+        self.cpp_testing_codegen: set[str] = set()
 
     def reset(self):
         from esphome.pins import PIN_SCHEMA_REGISTRY
@@ -644,6 +648,8 @@ class EsphomeCore:
         self.current_component = None
         self.address_cache = None
         self._config_hash = None
+        self.cpp_testing = False
+        self.cpp_testing_codegen = set()
         PIN_SCHEMA_REGISTRY.reset()
 
     @contextmanager
@@ -987,6 +993,15 @@ class EsphomeCore:
         """
         self.platform_counts[platform_name] += 1
 
+    def testing_ensure_platform_registered(self, platform_name: str) -> None:
+        """Ensure a platform has at least one entity registered for testing.
+
+        Used during C++ test builds to guarantee USE_* defines are emitted
+        without needing a real component variable.
+        """
+        if not self.platform_counts[platform_name]:
+            self.platform_counts[platform_name] = 1
+
     def register_controller(self) -> None:
         """Track registration of a Controller for ControllerRegistry StaticVector sizing."""
         controller_count = self.data.setdefault(KEY_CONTROLLER_REGISTRY_COUNT, 0)
diff --git a/esphome/loader.py b/esphome/loader.py
index 968c8cf3e05..5771e074738 100644
--- a/esphome/loader.py
+++ b/esphome/loader.py
@@ -71,6 +71,11 @@ class ComponentManifest:
 
     @property
     def to_code(self) -> Callable[[Any], None] | None:
+        if CORE.cpp_testing:
+            # During C++ testing, only run to_code for allowlisted components
+            name = self.module.__package__.rsplit(".", 1)[-1]
+            if name not in CORE.cpp_testing_codegen:
+                return None
         return getattr(self.module, "to_code", None)
 
     @property
diff --git a/script/cpp_unit_test.py b/script/cpp_unit_test.py
index b87261ab332..e11687dc16d 100755
--- a/script/cpp_unit_test.py
+++ b/script/cpp_unit_test.py
@@ -10,9 +10,10 @@ from helpers import get_all_components, get_all_dependencies, root_path
 
 from esphome.__main__ import command_compile, parse_args
 from esphome.config import validate_config
+from esphome.const import CONF_PLATFORM
 from esphome.core import CORE
+from esphome.loader import get_component
 from esphome.platformio_api import get_idedata
-from esphome.yaml_util import load_yaml
 
 # This must coincide with the version in /platformio.ini
 PLATFORMIO_GOOGLE_TEST_LIB = "google/googletest@^1.15.2"
@@ -20,6 +21,13 @@ PLATFORMIO_GOOGLE_TEST_LIB = "google/googletest@^1.15.2"
 # Path to /tests/components
 COMPONENTS_TESTS_DIR: Path = Path(root_path) / "tests" / "components"
 
+# Components whose to_code should run during C++ test builds.
+# Most components don't need code generation for tests; only these
+# essential ones (platform setup, logging, core config) are needed.
+# Note: "core" is the esphome core config module (esphome/core/config.py),
+# which registers under package name "core" not "esphome".
+CPP_TESTING_CODEGEN_COMPONENTS = {"core", "host", "logger"}
+
 
 def hash_components(components: list[str]) -> str:
     key = ",".join(components)
@@ -30,12 +38,14 @@ def filter_components_without_tests(components: list[str]) -> list[str]:
     """Filter out components that do not have a corresponding test file.
 
     This is done by checking if the component's directory contains at
-    least a .cpp file.
+    least a .cpp or .h file.
     """
     filtered_components: list[str] = []
     for component in components:
         test_dir = COMPONENTS_TESTS_DIR / component
-        if test_dir.is_dir() and any(test_dir.glob("*.cpp")):
+        if test_dir.is_dir() and (
+            any(test_dir.glob("*.cpp")) or any(test_dir.glob("*.h"))
+        ):
             filtered_components.append(component)
         else:
             print(
@@ -45,38 +55,6 @@ def filter_components_without_tests(components: list[str]) -> list[str]:
     return filtered_components
 
 
-# Name of optional per-component YAML config merged into the test build
-# before validation so that platform defines (USE_SENSOR, etc.) are generated.
-CPP_TEST_CONFIG_FILE = "cpp_test.yaml"
-
-
-def load_component_test_configs(components: list[str]) -> dict:
-    """Load cpp_test.yaml files from test component directories.
-
-    These configs are merged into the base test config *before* validation
-    so that entity registration runs during code generation, which causes
-    the corresponding USE_* defines to be emitted.
-    """
-    merged: dict = {}
-    for component in components:
-        config_file = COMPONENTS_TESTS_DIR / component / CPP_TEST_CONFIG_FILE
-        if not config_file.exists():
-            continue
-        component_config = load_yaml(config_file)
-        if not component_config:
-            continue
-        for key, value in component_config.items():
-            if (
-                key in merged
-                and isinstance(merged[key], list)
-                and isinstance(value, list)
-            ):
-                merged[key].extend(value)
-            else:
-                merged[key] = value
-    return merged
-
-
 def create_test_config(config_name: str, includes: list[str]) -> dict:
     """Create ESPHome test configuration for C++ unit tests.
 
@@ -113,11 +91,52 @@ def create_test_config(config_name: str, includes: list[str]) -> dict:
     }
 
 
+def get_platform_components(components: list[str]) -> list[str]:
+    """Discover platform sub-components referenced by test directory structure.
+
+    For each component being tested, any sub-directory named after a platform
+    domain (e.g. ``sensor``, ``binary_sensor``) is treated as a request to
+    include that ``<domain>.<component>`` platform in the build.  The sub-
+    directory must name a valid platform domain; anything else raises an error
+    so that typos are caught early.
+
+    Returns:
+        List of ``"domain.component"`` strings, one per discovered sub-directory.
+    """
+    platform_components: list[str] = []
+    for component in components:
+        test_dir = COMPONENTS_TESTS_DIR / component
+        if not test_dir.is_dir():
+            continue
+        # Each sub-directory name is expected to be a platform domain
+        # (e.g. tests/components/bthome/sensor/ → sensor.bthome).
+        for domain_dir in test_dir.iterdir():
+            if not domain_dir.is_dir():
+                continue
+            domain = domain_dir.name
+            domain_module = get_component(domain)
+            if domain_module is None or not domain_module.is_platform_component:
+                raise ValueError(
+                    f"Component tests for '{component}' reference non-existing or invalid domain '{domain}'"
+                    f" in its directory structure. See ({COMPONENTS_TESTS_DIR / component / domain})."
+                )
+            platform_components.append(f"{domain}.{component}")
+    return platform_components
+
+
+# Exit codes for run_tests
+EXIT_OK = 0
+EXIT_SKIPPED = 1
+EXIT_COMPILE_ERROR = 2
+EXIT_CONFIG_ERROR = 3
+EXIT_NO_EXECUTABLE = 4
+
+
 def run_tests(selected_components: list[str]) -> int:
     # Skip tests on Windows
     if os.name == "nt":
         print("Skipping esphome tests on Windows", file=sys.stderr)
-        return 1
+        return EXIT_SKIPPED
 
     # Remove components that do not have tests
     components = filter_components_without_tests(selected_components)
@@ -127,45 +146,63 @@ def run_tests(selected_components: list[str]) -> int:
             "No components specified or no tests found for the specified components.",
             file=sys.stderr,
         )
-        return 0
+        return EXIT_OK
 
     components = sorted(components)
 
-    # Obtain possible dependencies for the requested components.
-    # Always include 'time' because USE_TIME_TIMEZONE is defined as a build flag,
-    # which causes core/time.h to include components/time/posix_tz.h.
-    components_with_dependencies = sorted(
-        get_all_dependencies(set(components) | {"time"})
-    )
-
-    # Build a list of include folders, one folder per component containing tests.
-    # A special replacement main.cpp is located in /tests/components/main.cpp
+    # Build a list of include folders relative to COMPONENTS_TESTS_DIR. These folders will
+    # be added along with their subfolders.
+    # "main.cpp" is a special entry that points to /tests/components/main.cpp,
+    # which provides a custom test runner entry-point replacing the default one.
+    # Each remaining entry is a component folder whose *.cpp files are compiled.
     includes: list[str] = ["main.cpp"] + components
 
+    # Obtain a list of platform components to be tested:
+    try:
+        platform_components = get_platform_components(components)
+    except ValueError as e:
+        print(f"Error obtaining platform components: {e}")
+        return EXIT_CONFIG_ERROR
+
+    components = sorted(components + platform_components)
+
     # Create a unique name for this config based on the actual components being tested
     # to maximize cache during testing
     config_name: str = "cpptests-" + hash_components(components)
 
-    config = create_test_config(config_name, includes)
+    # Obtain possible dependencies for the requested components.
+    # Always include 'time' because USE_TIME_TIMEZONE is defined as a build flag,
+    # which causes core/time.h to include components/time/posix_tz.h.
+    components_with_dependencies: list[str] = sorted(
+        get_all_dependencies(set(components) | {"time"}, cpp_testing=True)
+    )
 
-    # Merge component-specific test configs (e.g. sensor instances) before
-    # validation so that entity registration and USE_* defines work.
-    extra_config = load_component_test_configs(components)
-    config.update(extra_config)
+    config = create_test_config(config_name, includes)
 
     CORE.config_path = COMPONENTS_TESTS_DIR / "dummy.yaml"
     CORE.dashboard = None
+    CORE.cpp_testing = True
+    CORE.cpp_testing_codegen = CPP_TESTING_CODEGEN_COMPONENTS
 
     # Validate config will expand the above with defaults:
     config = validate_config(config, {})
 
     # Add all components and dependencies to the base configuration after validation, so their files
-    # are added to the build.  Use setdefault to avoid overwriting entries that were
-    # already validated (e.g. sensor instances from cpp_test.yaml).
-    for key in components_with_dependencies:
-        config.setdefault(key, {})
+    # are added to the build.
+    for component_name in components_with_dependencies:
+        if "." in component_name:
+            # Format is always "domain.component" (exactly one dot),
+            # as produced by get_platform_components().
+            domain, component = component_name.split(".", maxsplit=1)
+            domain_list = config.setdefault(domain, [])
+            CORE.testing_ensure_platform_registered(domain)
+            domain_list.append({CONF_PLATFORM: component})
+        else:
+            config.setdefault(component_name, [])
 
-    print(f"Testing components: {', '.join(components)}")
+    dependencies = set(components_with_dependencies) - set(components)
+    deps_str = ", ".join(dependencies) if dependencies else "None"
+    print(f"Testing components: {', '.join(components)}. Dependencies: {deps_str}")
     CORE.config = config
     args = parse_args(["program", "compile", str(CORE.config_path)])
     try:
@@ -178,13 +215,13 @@ def run_tests(selected_components: list[str]) -> int:
         print(
             f"Error compiling unit tests for {', '.join(components)}. Check path. : {e}"
         )
-        return 2
+        return EXIT_COMPILE_ERROR
 
     # After a successful compilation, locate the executable and run it:
     idedata = get_idedata(config)
     if idedata is None:
         print("Cannot find executable")
-        return 1
+        return EXIT_NO_EXECUTABLE
 
     program_path: str = idedata.raw["prog_path"]
     run_cmd: list[str] = [program_path]
diff --git a/script/helpers.py b/script/helpers.py
index d372d2a7ec4..6ee286a657f 100644
--- a/script/helpers.py
+++ b/script/helpers.py
@@ -15,6 +15,8 @@ from typing import Any
 
 import colorama
 
+from esphome.loader import get_platform
+
 root_path = os.path.abspath(os.path.normpath(os.path.join(__file__, "..", "..")))
 basepath = os.path.join(root_path, "esphome")
 temp_folder = os.path.join(root_path, ".temp")
@@ -624,11 +626,15 @@ def get_usable_cpu_count() -> int:
     )
 
 
-def get_all_dependencies(component_names: set[str]) -> set[str]:
+def get_all_dependencies(
+    component_names: set[str], cpp_testing: bool = False
+) -> set[str]:
     """Get all dependencies for a set of components.
 
     Args:
         component_names: Set of component names to get dependencies for
+        cpp_testing: If True, set CORE.cpp_testing so AUTO_LOAD callables that
+                     conditionally include testing-only dependencies work correctly
 
     Returns:
         Set of all components including dependencies and auto-loaded components
@@ -646,6 +652,7 @@ def get_all_dependencies(component_names: set[str]) -> set[str]:
 
     # Reset CORE to ensure clean state
     CORE.reset()
+    CORE.cpp_testing = cpp_testing
 
     # Set up fake config path for component loading
     root = Path(__file__).parent.parent
@@ -660,7 +667,11 @@ def get_all_dependencies(component_names: set[str]) -> set[str]:
         new_components: set[str] = set()
 
         for comp_name in all_components:
-            comp = get_component(comp_name)
+            if "." in comp_name:
+                domain, platform = comp_name.split(".", maxsplit=1)
+                comp = get_platform(domain, platform)
+            else:
+                comp = get_component(comp_name)
             if not comp:
                 continue
 
diff --git a/tests/components/README.md b/tests/components/README.md
index 0901f2ef177..6da0dadd25e 100644
--- a/tests/components/README.md
+++ b/tests/components/README.md
@@ -7,10 +7,23 @@
 testing binaries that combine many components. By convention, this unique namespace is `esphome::component::testing`
 (where "component" is the component under test), for example: `esphome::uart::testing`.
 
+### Platform components
+
+For components that expose to a platform component, create a folder under your component test folder with the platform component name, e.g. `binary_sensor` and
+include the relevant `.cpp` and `.h` test files there.
+
+### Override component code generation for testing
+
+When generating code for testing, ESPHome won't invoke the component's `to_code` function, since most components do not
+need to generate configuration code for testing.
+
+If you do need to generate code to for example configure compilation flags or add libraries,
+add the component name to the `CPP_TESTING_CODEGEN_COMPONENTS` allowlist in `script/cpp_unit_test.py`.
 
 ## Running component unit tests
 
 (from the repository root)
+
 ```bash
 ./script/cpp_unit_test.py component1 component2 ...
 ```
diff --git a/tests/components/packet_transport/binary_sensor/binary_sensor_test.cpp b/tests/components/packet_transport/binary_sensor/binary_sensor_test.cpp
new file mode 100644
index 00000000000..36af087d2c2
--- /dev/null
+++ b/tests/components/packet_transport/binary_sensor/binary_sensor_test.cpp
@@ -0,0 +1,77 @@
+#include "../common.h"
+
+namespace esphome::packet_transport::testing {
+
+TEST(PacketTransportBinarySensorTest, AddBinarySensor) {
+  TestablePacketTransport transport;
+  binary_sensor::BinarySensor bs;
+  transport.add_binary_sensor("motion", &bs);
+  ASSERT_EQ(transport.binary_sensors_.size(), 1u);
+  EXPECT_STREQ(transport.binary_sensors_[0].id, "motion");
+  EXPECT_EQ(transport.binary_sensors_[0].sensor, &bs);
+}
+
+TEST(PacketTransportBinarySensorTest, AddRemoteBinarySensor) {
+  TestablePacketTransport transport;
+  binary_sensor::BinarySensor bs;
+  transport.add_remote_binary_sensor("host1", "remote_motion", &bs);
+  EXPECT_TRUE(transport.providers_.contains("host1"));
+  EXPECT_EQ(transport.remote_binary_sensors_["host1"]["remote_motion"], &bs);
+}
+
+TEST(PacketTransportBinarySensorTest, UnencryptedBinarySensorRoundTrip) {
+  TestablePacketTransport encoder;
+  encoder.init_for_test("sender");
+  binary_sensor::BinarySensor local_bs;
+  local_bs.state = true;
+  encoder.add_binary_sensor("motion", &local_bs);
+
+  encoder.send_data_(true);
+  ASSERT_EQ(encoder.sent_packets.size(), 1u);
+
+  TestablePacketTransport decoder;
+  decoder.init_for_test("receiver");
+  binary_sensor::BinarySensor remote_bs;
+  decoder.add_remote_binary_sensor("sender", "motion", &remote_bs);
+
+  auto &packet = encoder.sent_packets[0];
+  decoder.process_({packet.data(), packet.size()});
+  EXPECT_TRUE(remote_bs.state);
+}
+
+TEST(PacketTransportBinarySensorTest, MultipleSensorsRoundTrip) {
+  TestablePacketTransport encoder;
+  encoder.init_for_test("sender");
+
+  sensor::Sensor s1, s2;
+  s1.state = 10.0f;
+  s2.state = 20.0f;
+  encoder.add_sensor("s1", &s1);
+  encoder.add_sensor("s2", &s2);
+
+  binary_sensor::BinarySensor bs1;
+  bs1.state = true;
+  encoder.add_binary_sensor("bs1", &bs1);
+
+  encoder.send_data_(true);
+  ASSERT_EQ(encoder.sent_packets.size(), 1u);
+
+  TestablePacketTransport decoder;
+  decoder.init_for_test("receiver");
+  sensor::Sensor rs1, rs2;
+  binary_sensor::BinarySensor rbs1;
+  rs1.state = -999.0f;
+  rs2.state = -999.0f;
+  decoder.add_remote_sensor("sender", "s1", &rs1);
+  decoder.add_remote_sensor("sender", "s2", &rs2);
+  decoder.add_remote_binary_sensor("sender", "bs1", &rbs1);
+
+  auto &packet = encoder.sent_packets[0];
+  decoder.process_({packet.data(), packet.size()});
+
+  EXPECT_FLOAT_EQ(rs1.state, 10.0f);
+  EXPECT_FLOAT_EQ(rs2.state, 20.0f);
+  EXPECT_TRUE(rbs1.state);
+}
+
+}  // namespace esphome::packet_transport::testing
diff --git a/tests/components/packet_transport/cpp_test.yaml b/tests/components/packet_transport/cpp_test.yaml
deleted file mode 100644
index fa39df3c0ae..00000000000
--- a/tests/components/packet_transport/cpp_test.yaml
+++ /dev/null
@@ -1,11 +0,0 @@
-# Extra component configuration required by C++ unit tests.
-# Loaded by cpp_unit_test.py and merged into the test build config
-# before validation, so that platform defines (USE_SENSOR, etc.) are generated.
-
-sensor:
-  - platform: template
-    id: test_cpp_sensor
-
-binary_sensor:
-  - platform: template
-    id: test_cpp_binary_sensor
diff --git a/tests/components/packet_transport/packet_transport_test.cpp b/tests/components/packet_transport/packet_transport_test.cpp
index d8f11ca6072..59c0a88ed7c 100644
--- a/tests/components/packet_transport/packet_transport_test.cpp
+++ b/tests/components/packet_transport/packet_transport_test.cpp
@@ -65,198 +65,6 @@ TEST(PacketTransportTest, SetProviderEncryption) {
   EXPECT_EQ(transport.providers_["host1"].encryption_key, key);
 }
 
-// --- Sensor management (requires USE_SENSOR / USE_BINARY_SENSOR) ---
-
-#ifdef USE_SENSOR
-TEST(PacketTransportTest, AddSensor) {
-  TestablePacketTransport transport;
-  sensor::Sensor s;
-  transport.add_sensor("temp", &s);
-  ASSERT_EQ(transport.sensors_.size(), 1u);
-  EXPECT_STREQ(transport.sensors_[0].id, "temp");
-  EXPECT_EQ(transport.sensors_[0].sensor, &s);
-  EXPECT_TRUE(transport.sensors_[0].updated);
-}
-
-TEST(PacketTransportTest, AddRemoteSensor) {
-  TestablePacketTransport transport;
-  sensor::Sensor s;
-  transport.add_remote_sensor("host1", "remote_temp", &s);
-  EXPECT_TRUE(transport.providers_.contains("host1"));
-  EXPECT_EQ(transport.remote_sensors_["host1"]["remote_temp"], &s);
-}
-#endif
-
-#ifdef USE_BINARY_SENSOR
-TEST(PacketTransportTest, AddBinarySensor) {
-  TestablePacketTransport transport;
-  binary_sensor::BinarySensor bs;
-  transport.add_binary_sensor("motion", &bs);
-  ASSERT_EQ(transport.binary_sensors_.size(), 1u);
-  EXPECT_STREQ(transport.binary_sensors_[0].id, "motion");
-  EXPECT_EQ(transport.binary_sensors_[0].sensor, &bs);
-}
-
-TEST(PacketTransportTest, AddRemoteBinarySensor) {
-  TestablePacketTransport transport;
-  binary_sensor::BinarySensor bs;
-  transport.add_remote_binary_sensor("host1", "remote_motion", &bs);
-  EXPECT_TRUE(transport.providers_.contains("host1"));
-  EXPECT_EQ(transport.remote_binary_sensors_["host1"]["remote_motion"], &bs);
-}
-#endif
-
-// --- Unencrypted round-trip tests (require USE_SENSOR / USE_BINARY_SENSOR) ---
-
-#ifdef USE_SENSOR
-TEST(PacketTransportTest, UnencryptedSensorRoundTrip) {
-  // Encoder
-  TestablePacketTransport encoder;
-  encoder.init_for_test("sender");
-  sensor::Sensor local_sensor;
-  local_sensor.state = 42.5f;
-  encoder.add_sensor("temp", &local_sensor);
-
-  encoder.send_data_(true);
-  ASSERT_EQ(encoder.sent_packets.size(), 1u);
-
-  // Decoder
-  TestablePacketTransport decoder;
-  decoder.init_for_test("receiver");
-  sensor::Sensor remote_sensor;
-  remote_sensor.state = -999.0f;  // sentinel
-  decoder.add_remote_sensor("sender", "temp", &remote_sensor);
-
-  auto &packet = encoder.sent_packets[0];
-  decoder.process_({packet.data(), packet.size()});
-  EXPECT_FLOAT_EQ(remote_sensor.state, 42.5f);
-}
-#endif
-
-#ifdef USE_BINARY_SENSOR
-TEST(PacketTransportTest, UnencryptedBinarySensorRoundTrip) {
-  TestablePacketTransport encoder;
-  encoder.init_for_test("sender");
-  binary_sensor::BinarySensor local_bs;
-  local_bs.state = true;
-  encoder.add_binary_sensor("motion", &local_bs);
-
-  encoder.send_data_(true);
-  ASSERT_EQ(encoder.sent_packets.size(), 1u);
-
-  TestablePacketTransport decoder;
-  decoder.init_for_test("receiver");
-  binary_sensor::BinarySensor remote_bs;
-  decoder.add_remote_binary_sensor("sender", "motion", &remote_bs);
-
-  auto &packet = encoder.sent_packets[0];
-  decoder.process_({packet.data(), packet.size()});
-  EXPECT_TRUE(remote_bs.state);
-}
-#endif
-
-#if defined(USE_SENSOR) && defined(USE_BINARY_SENSOR)
-TEST(PacketTransportTest, MultipleSensorsRoundTrip) {
-  TestablePacketTransport encoder;
-  encoder.init_for_test("sender");
-
-  sensor::Sensor s1, s2;
-  s1.state = 10.0f;
-  s2.state = 20.0f;
-  encoder.add_sensor("s1", &s1);
-  encoder.add_sensor("s2", &s2);
-
-  binary_sensor::BinarySensor bs1;
-  bs1.state = true;
-  encoder.add_binary_sensor("bs1", &bs1);
-
-  encoder.send_data_(true);
-  ASSERT_EQ(encoder.sent_packets.size(), 1u);
-
-  TestablePacketTransport decoder;
-  decoder.init_for_test("receiver");
-  sensor::Sensor rs1, rs2;
-  binary_sensor::BinarySensor rbs1;
-  rs1.state = -999.0f;
-  rs2.state = -999.0f;
-  decoder.add_remote_sensor("sender", "s1", &rs1);
-  decoder.add_remote_sensor("sender", "s2", &rs2);
-  decoder.add_remote_binary_sensor("sender", "bs1", &rbs1);
-
-  auto &packet = encoder.sent_packets[0];
-  decoder.process_({packet.data(), packet.size()});
-
-  EXPECT_FLOAT_EQ(rs1.state, 10.0f);
-  EXPECT_FLOAT_EQ(rs2.state, 20.0f);
-  EXPECT_TRUE(rbs1.state);
-}
-#endif
-
-// --- Encrypted round-trip ---
-
-#ifdef USE_SENSOR
-TEST(PacketTransportTest, EncryptedSensorRoundTrip) {
-  std::vector<uint8_t> key(32);
-  for (int i = 0; i < 32; i++)
-    key[i] = i;
-
-  TestablePacketTransport encoder;
-  encoder.init_for_test("sender");
-  encoder.set_encryption_key(key);
-  sensor::Sensor local_sensor;
-  local_sensor.state = 99.9f;
-  encoder.add_sensor("temp", &local_sensor);
-
-  encoder.send_data_(true);
-  ASSERT_EQ(encoder.sent_packets.size(), 1u);
-
-  TestablePacketTransport decoder;
-  decoder.init_for_test("receiver");
-  sensor::Sensor remote_sensor;
-  remote_sensor.state = -999.0f;
-  decoder.add_remote_sensor("sender", "temp", &remote_sensor);
-  decoder.set_provider_encryption("sender", key);
-
-  auto &packet = encoder.sent_packets[0];
-  decoder.process_({packet.data(), packet.size()});
-  EXPECT_FLOAT_EQ(remote_sensor.state, 99.9f);
-}
-
-// --- Selective send ---
-
-TEST(PacketTransportTest, SendDataOnlyUpdated) {
-  TestablePacketTransport encoder;
-  encoder.init_for_test("sender");
-
-  sensor::Sensor s1, s2;
-  s1.state = 1.0f;
-  s2.state = 2.0f;
-  encoder.add_sensor("s1", &s1);
-  encoder.add_sensor("s2", &s2);
-
-  // Mark s1 as not updated, only s2 as updated
-  encoder.sensors_[0].updated = false;
-  encoder.sensors_[1].updated = true;
-
-  encoder.send_data_(false);
-  ASSERT_EQ(encoder.sent_packets.size(), 1u);
-
-  TestablePacketTransport decoder;
-  decoder.init_for_test("receiver");
-  sensor::Sensor rs1, rs2;
-  rs1.state = -999.0f;
-  rs2.state = -999.0f;
-  decoder.add_remote_sensor("sender", "s1", &rs1);
-  decoder.add_remote_sensor("sender", "s2", &rs2);
-
-  auto &packet = encoder.sent_packets[0];
-  decoder.process_({packet.data(), packet.size()});
-
-  EXPECT_FLOAT_EQ(rs1.state, -999.0f);  // not updated, not sent
-  EXPECT_FLOAT_EQ(rs2.state, 2.0f);     // updated, sent
-}
-#endif
-
 // --- Ping key tests ---
 
 TEST(PacketTransportTest, PingKeyStoredWhenEncrypted) {
@@ -319,73 +127,6 @@ TEST(PacketTransportTest, PingKeyMaxLimit) {
   EXPECT_FALSE(transport.ping_keys_.contains("host4"));
 }
 
-#ifdef USE_SENSOR
-TEST(PacketTransportTest, PingKeyIncludedInTransmittedPacket) {
-  std::vector<uint8_t> key(32, 0xBB);
-
-  // Responder: encrypted, owns a sensor
-  TestablePacketTransport responder;
-  responder.init_for_test("responder");
-  responder.set_encryption_key(key);
-  sensor::Sensor local_sensor;
-  local_sensor.state = 77.7f;
-  responder.add_sensor("temp", &local_sensor);
-
-  // Requester sends a MAGIC_PING that the responder processes
-  auto ping = build_ping_packet("requester", 0xDEADBEEF);
-  responder.process_({ping.data(), ping.size()});
-  ASSERT_EQ(responder.ping_keys_.size(), 1u);
-
-  // Responder sends sensor data — ping key should be embedded
-  responder.send_data_(true);
-  ASSERT_EQ(responder.sent_packets.size(), 1u);
-
-  // Requester: encrypted provider, ping-pong enabled, expects key 0xDEADBEEF
-  TestablePacketTransport requester;
-  requester.init_for_test("requester");
-  requester.set_ping_pong_enable(true);
-  requester.ping_key_ = 0xDEADBEEF;
-  sensor::Sensor remote_sensor;
-  remote_sensor.state = -999.0f;
-  requester.add_remote_sensor("responder", "temp", &remote_sensor);
-  requester.set_provider_encryption("responder", key);
-
-  // The requester decrypts the packet and finds its ping key echoed back,
-  // which gates the sensor data — if the key is missing, data is blocked.
-  auto &packet = responder.sent_packets[0];
-  requester.process_({packet.data(), packet.size()});
-  EXPECT_FLOAT_EQ(remote_sensor.state, 77.7f);
-}
-
-TEST(PacketTransportTest, MissingPingKeyBlocksSensorData) {
-  std::vector<uint8_t> key(32, 0xBB);
-
-  // Responder sends data WITHOUT receiving any MAGIC_PING first — no ping keys
-  TestablePacketTransport responder;
-  responder.init_for_test("responder");
-  responder.set_encryption_key(key);
-  sensor::Sensor local_sensor;
-  local_sensor.state = 77.7f;
-  responder.add_sensor("temp", &local_sensor);
-  responder.send_data_(true);
-  ASSERT_EQ(responder.sent_packets.size(), 1u);
-
-  // Requester with ping-pong enabled expects a key that isn't in the packet
-  TestablePacketTransport requester;
-  requester.init_for_test("requester");
-  requester.set_ping_pong_enable(true);
-  requester.ping_key_ = 0xDEADBEEF;
-  sensor::Sensor remote_sensor;
-  remote_sensor.state = -999.0f;
-  requester.add_remote_sensor("responder", "temp", &remote_sensor);
-  requester.set_provider_encryption("responder", key);
-
-  auto &packet = responder.sent_packets[0];
-  requester.process_({packet.data(), packet.size()});
-  EXPECT_FLOAT_EQ(remote_sensor.state, -999.0f);  // blocked — ping key not found
-}
-#endif
-
 // --- Process error handling ---
 
 TEST(PacketTransportTest, ProcessShortBuffer) {
diff --git a/tests/components/packet_transport/sensor/sensor_test.cpp b/tests/components/packet_transport/sensor/sensor_test.cpp
new file mode 100644
index 00000000000..2f681aee587
--- /dev/null
+++ b/tests/components/packet_transport/sensor/sensor_test.cpp
@@ -0,0 +1,170 @@
+#include "../common.h"
+
+namespace esphome::packet_transport::testing {
+
+TEST(PacketTransportSensorTest, AddSensor) {
+  TestablePacketTransport transport;
+  sensor::Sensor s;
+  transport.add_sensor("temp", &s);
+  ASSERT_EQ(transport.sensors_.size(), 1u);
+  EXPECT_STREQ(transport.sensors_[0].id, "temp");
+  EXPECT_EQ(transport.sensors_[0].sensor, &s);
+  EXPECT_TRUE(transport.sensors_[0].updated);
+}
+
+TEST(PacketTransportSensorTest, AddRemoteSensor) {
+  TestablePacketTransport transport;
+  sensor::Sensor s;
+  transport.add_remote_sensor("host1", "remote_temp", &s);
+  EXPECT_TRUE(transport.providers_.contains("host1"));
+  EXPECT_EQ(transport.remote_sensors_["host1"]["remote_temp"], &s);
+}
+
+TEST(PacketTransportSensorTest, UnencryptedSensorRoundTrip) {
+  // Encoder
+  TestablePacketTransport encoder;
+  encoder.init_for_test("sender");
+  sensor::Sensor local_sensor;
+  local_sensor.state = 42.5f;
+  encoder.add_sensor("temp", &local_sensor);
+
+  encoder.send_data_(true);
+  ASSERT_EQ(encoder.sent_packets.size(), 1u);
+
+  // Decoder
+  TestablePacketTransport decoder;
+  decoder.init_for_test("receiver");
+  sensor::Sensor remote_sensor;
+  remote_sensor.state = -999.0f;  // sentinel
+  decoder.add_remote_sensor("sender", "temp", &remote_sensor);
+
+  auto &packet = encoder.sent_packets[0];
+  decoder.process_({packet.data(), packet.size()});
+  EXPECT_FLOAT_EQ(remote_sensor.state, 42.5f);
+}
+
+TEST(PacketTransportSensorTest, EncryptedSensorRoundTrip) {
+  std::vector<uint8_t> key(32);
+  for (int i = 0; i < 32; i++)
+    key[i] = i;
+
+  TestablePacketTransport encoder;
+  encoder.init_for_test("sender");
+  encoder.set_encryption_key(key);
+  sensor::Sensor local_sensor;
+  local_sensor.state = 99.9f;
+  encoder.add_sensor("temp", &local_sensor);
+
+  encoder.send_data_(true);
+  ASSERT_EQ(encoder.sent_packets.size(), 1u);
+
+  TestablePacketTransport decoder;
+  decoder.init_for_test("receiver");
+  sensor::Sensor remote_sensor;
+  remote_sensor.state = -999.0f;
+  decoder.add_remote_sensor("sender", "temp", &remote_sensor);
+  decoder.set_provider_encryption("sender", key);
+
+  auto &packet = encoder.sent_packets[0];
+  decoder.process_({packet.data(), packet.size()});
+  EXPECT_FLOAT_EQ(remote_sensor.state, 99.9f);
+}
+
+TEST(PacketTransportSensorTest, SendDataOnlyUpdated) {
+  TestablePacketTransport encoder;
+  encoder.init_for_test("sender");
+
+  sensor::Sensor s1, s2;
+  s1.state = 1.0f;
+  s2.state = 2.0f;
+  encoder.add_sensor("s1", &s1);
+  encoder.add_sensor("s2", &s2);
+
+  // Mark s1 as not updated, only s2 as updated
+  encoder.sensors_[0].updated = false;
+  encoder.sensors_[1].updated = true;
+
+  encoder.send_data_(false);
+  ASSERT_EQ(encoder.sent_packets.size(), 1u);
+
+  TestablePacketTransport decoder;
+  decoder.init_for_test("receiver");
+  sensor::Sensor rs1, rs2;
+  rs1.state = -999.0f;
+  rs2.state = -999.0f;
+  decoder.add_remote_sensor("sender", "s1", &rs1);
+  decoder.add_remote_sensor("sender", "s2", &rs2);
+
+  auto &packet = encoder.sent_packets[0];
+  decoder.process_({packet.data(), packet.size()});
+
+  EXPECT_FLOAT_EQ(rs1.state, -999.0f);  // not updated, not sent
+  EXPECT_FLOAT_EQ(rs2.state, 2.0f);     // updated, sent
+}
+
+TEST(PacketTransportSensorTest, PingKeyIncludedInTransmittedPacket) {
+  std::vector<uint8_t> key(32, 0xBB);
+
+  // Responder: encrypted, owns a sensor
+  TestablePacketTransport responder;
+  responder.init_for_test("responder");
+  responder.set_encryption_key(key);
+  sensor::Sensor local_sensor;
+  local_sensor.state = 77.7f;
+  responder.add_sensor("temp", &local_sensor);
+
+  // Requester sends a MAGIC_PING that the responder processes
+  auto ping = build_ping_packet("requester", 0xDEADBEEF);
+  responder.process_({ping.data(), ping.size()});
+  ASSERT_EQ(responder.ping_keys_.size(), 1u);
+
+  // Responder sends sensor data — ping key should be embedded
+  responder.send_data_(true);
+  ASSERT_EQ(responder.sent_packets.size(), 1u);
+
+  // Requester: encrypted provider, ping-pong enabled, expects key 0xDEADBEEF
+  TestablePacketTransport requester;
+  requester.init_for_test("requester");
+  requester.set_ping_pong_enable(true);
+  requester.ping_key_ = 0xDEADBEEF;
+  sensor::Sensor remote_sensor;
+  remote_sensor.state = -999.0f;
+  requester.add_remote_sensor("responder", "temp", &remote_sensor);
+  requester.set_provider_encryption("responder", key);
+
+  // The requester decrypts the packet and finds its ping key echoed back,
+  // which gates the sensor data — if the key is missing, data is blocked.
+  auto &packet = responder.sent_packets[0];
+  requester.process_({packet.data(), packet.size()});
+  EXPECT_FLOAT_EQ(remote_sensor.state, 77.7f);
+}
+
+TEST(PacketTransportSensorTest, MissingPingKeyBlocksSensorData) {
+  std::vector<uint8_t> key(32, 0xBB);
+
+  // Responder sends data WITHOUT receiving any MAGIC_PING first — no ping keys
+  TestablePacketTransport responder;
+  responder.init_for_test("responder");
+  responder.set_encryption_key(key);
+  sensor::Sensor local_sensor;
+  local_sensor.state = 77.7f;
+  responder.add_sensor("temp", &local_sensor);
+  responder.send_data_(true);
+  ASSERT_EQ(responder.sent_packets.size(), 1u);
+
+  // Requester with ping-pong enabled expects a key that isn't in the packet
+  TestablePacketTransport requester;
+  requester.init_for_test("requester");
+  requester.set_ping_pong_enable(true);
+  requester.ping_key_ = 0xDEADBEEF;
+  sensor::Sensor remote_sensor;
+  remote_sensor.state = -999.0f;
+  requester.add_remote_sensor("responder", "temp", &remote_sensor);
+  requester.set_provider_encryption("responder", key);
+
+  auto &packet = responder.sent_packets[0];
+  requester.process_({packet.data(), packet.size()});
+  EXPECT_FLOAT_EQ(remote_sensor.state, -999.0f);  // blocked — ping key not found
+}
+
+}  // namespace esphome::packet_transport::testing
diff --git a/tests/script/test_helpers.py b/tests/script/test_helpers.py
index 2953a9fd428..781054eb3b9 100644
--- a/tests/script/test_helpers.py
+++ b/tests/script/test_helpers.py
@@ -1027,6 +1027,73 @@ def test_get_all_dependencies_empty_set() -> None:
     assert result == set()
 
 
+def test_get_all_dependencies_platform_component() -> None:
+    """Platform components (domain.component) are looked up via get_platform,
+    not get_component."""
+    platform_comp = Mock()
+    platform_comp.dependencies = []
+    platform_comp.auto_load = []
+
+    with (
+        patch("esphome.loader.get_component") as mock_get_component,
+        patch("helpers.get_platform") as mock_get_platform,
+    ):
+        mock_get_platform.return_value = platform_comp
+        mock_get_component.return_value = None
+
+        result = helpers.get_all_dependencies({"sensor.bthome"})
+
+        mock_get_platform.assert_called_once_with("sensor", "bthome")
+        mock_get_component.assert_not_called()
+        assert result == {"sensor.bthome"}
+
+
+def test_get_all_dependencies_platform_component_with_dependencies() -> None:
+    """Dependencies of a platform component are resolved transitively."""
+    platform_comp = Mock()
+    platform_comp.dependencies = ["sensor"]
+    platform_comp.auto_load = []
+
+    sensor_comp = Mock()
+    sensor_comp.dependencies = []
+    sensor_comp.auto_load = []
+
+    with (
+        patch("esphome.loader.get_component") as mock_get_component,
+        patch("helpers.get_platform") as mock_get_platform,
+    ):
+        mock_get_platform.return_value = platform_comp
+        mock_get_component.side_effect = lambda name: (
+            sensor_comp if name == "sensor" else None
+        )
+
+        result = helpers.get_all_dependencies({"sensor.bthome"})
+
+        assert result == {"sensor.bthome", "sensor"}
+
+
+def test_get_all_dependencies_cpp_testing_flag() -> None:
+    """cpp_testing=True propagates to CORE.cpp_testing during resolution."""
+    from esphome.core import CORE
+
+    with (
+        patch("esphome.loader.get_component") as mock_get_component,
+        patch("esphome.loader.get_platform"),
+    ):
+        observed: list[bool] = []
+
+        def capturing_get_component(name: str):
+            observed.append(CORE.cpp_testing)
+
+        mock_get_component.side_effect = capturing_get_component
+
+        helpers.get_all_dependencies({"some_comp"}, cpp_testing=True)
+
+    assert observed and all(observed), (
+        "CORE.cpp_testing should be True during resolution"
+    )
+
+
 def test_get_components_from_integration_fixtures() -> None:
     """Test extraction of components from fixture YAML files."""
     yaml_content = {
diff --git a/tests/unit_tests/test_core.py b/tests/unit_tests/test_core.py
index 174b3fec85d..22be59653aa 100644
--- a/tests/unit_tests/test_core.py
+++ b/tests/unit_tests/test_core.py
@@ -841,6 +841,18 @@ class TestEsphomeCore:
 
         assert "WiFi" in target.platformio_libraries
 
+    def test_testing_ensure_platform_registered__sets_count(self, target):
+        """Test testing_ensure_platform_registered sets count to 1 for new platform."""
+        assert target.platform_counts["sensor"] == 0
+        target.testing_ensure_platform_registered("sensor")
+        assert target.platform_counts["sensor"] == 1
+
+    def test_testing_ensure_platform_registered__does_not_overwrite(self, target):
+        """Test testing_ensure_platform_registered preserves existing count."""
+        target.platform_counts["sensor"] = 3
+        target.testing_ensure_platform_registered("sensor")
+        assert target.platform_counts["sensor"] == 3
+
     def test_add_library__extracts_short_name_from_path(self, target):
         """Test add_library extracts short name from library paths like owner/lib."""
         target.data[const.KEY_CORE] = {