C++ components unit test framework (#9284)

Co-authored-by: J. Nick Koston <nick@home-assistant.io>
Co-authored-by: J. Nick Koston <nick@koston.org>

.clang-tidy.hash

@@ -1 +1 @@
-d7693a1e996cacd4a3d1c9a16336799c2a8cc3db02e4e74084151ce964581248
+3d46b63015d761c85ca9cb77ab79a389509e5776701fb22aed16e7b79d432c0c

.github/workflows/ci.yml

@@ -178,6 +178,8 @@ jobs:
       component-test-count: ${{ steps.determine.outputs.component-test-count }}
       changed-cpp-file-count: ${{ steps.determine.outputs.changed-cpp-file-count }}
       memory_impact: ${{ steps.determine.outputs.memory-impact }}
+      cpp-unit-tests-run-all: ${{ steps.determine.outputs.cpp-unit-tests-run-all }}
+      cpp-unit-tests-components: ${{ steps.determine.outputs.cpp-unit-tests-components }}
     steps:
       - name: Check out code from GitHub
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
@@ -210,6 +212,8 @@ jobs:
           echo "component-test-count=$(echo "$output" | jq -r '.component_test_count')" >> $GITHUB_OUTPUT
           echo "changed-cpp-file-count=$(echo "$output" | jq -r '.changed_cpp_file_count')" >> $GITHUB_OUTPUT
           echo "memory-impact=$(echo "$output" | jq -c '.memory_impact')" >> $GITHUB_OUTPUT
+          echo "cpp-unit-tests-run-all=$(echo "$output" | jq -r '.cpp_unit_tests_run_all')" >> $GITHUB_OUTPUT
+          echo "cpp-unit-tests-components=$(echo "$output" | jq -c '.cpp_unit_tests_components')" >> $GITHUB_OUTPUT
 
   integration-tests:
     name: Run integration tests
@@ -247,6 +251,33 @@ jobs:
           . venv/bin/activate
           pytest -vv --no-cov --tb=native -n auto tests/integration/
 
+  cpp-unit-tests:
+    name: Run C++ unit tests
+    runs-on: ubuntu-24.04
+    needs:
+      - common
+      - determine-jobs
+    if: github.event_name == 'pull_request' && (needs.determine-jobs.outputs.cpp-unit-tests-run-all == 'true' || needs.determine-jobs.outputs.cpp-unit-tests-components != '[]')
+    steps:
+      - name: Check out code from GitHub
+        uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+
+      - name: Restore Python
+        uses: ./.github/actions/restore-python
+        with:
+          python-version: ${{ env.DEFAULT_PYTHON }}
+          cache-key: ${{ needs.common.outputs.cache-key }}
+
+      - name: Run cpp_unit_test.py
+        run: |
+          . venv/bin/activate
+          if [ "${{ needs.determine-jobs.outputs.cpp-unit-tests-run-all }}" = "true" ]; then
+            script/cpp_unit_test.py --all
+          else
+            ARGS=$(echo '${{ needs.determine-jobs.outputs.cpp-unit-tests-components }}' | jq -r '.[] | @sh' | xargs)
+            script/cpp_unit_test.py $ARGS
+          fi
+
   clang-tidy-single:
     name: ${{ matrix.name }}
     runs-on: ubuntu-24.04

platformio.ini

@@ -46,6 +46,10 @@ lib_deps =
     ; This is using the repository until a new release is published to PlatformIO
     https://github.com/Sensirion/arduino-gas-index-algorithm.git#3.2.1 ; Sensirion Gas Index Algorithm Arduino Library
     lvgl/lvgl@8.4.0                                       ; lvgl
+    ; This dependency is used only in unit tests.
+    ; Must coincide with PLATFORMIO_GOOGLE_TEST_LIB in scripts/cpp_unit_test.py
+    ; See scripts/cpp_unit_test.py and tests/components/README.md
+    google/googletest@^1.15.2
 build_flags =
     -DESPHOME_LOG_LEVEL=ESPHOME_LOG_LEVEL_VERY_VERBOSE
     -std=gnu++20

script/cpp_unit_test.py

@@ -0,0 +1,172 @@
+#!/usr/bin/env python3
+import argparse
+import hashlib
+import os
+from pathlib import Path
+import subprocess
+import sys
+
+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.core import CORE
+from esphome.platformio_api import get_idedata
+
+# This must coincide with the version in /platformio.ini
+PLATFORMIO_GOOGLE_TEST_LIB = "google/googletest@^1.15.2"
+
+# Path to /tests/components
+COMPONENTS_TESTS_DIR: Path = Path(root_path) / "tests" / "components"
+
+
+def hash_components(components: list[str]) -> str:
+    key = ",".join(components)
+    return hashlib.sha256(key.encode()).hexdigest()[:16]
+
+
+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.
+    """
+    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")):
+            filtered_components.append(component)
+        else:
+            print(
+                f"WARNING: No tests found for component '{component}', skipping.",
+                file=sys.stderr,
+            )
+    return filtered_components
+
+
+def create_test_config(config_name: str, includes: list[str]) -> dict:
+    """Create ESPHome test configuration for C++ unit tests.
+
+    Args:
+        config_name: Unique name for this test configuration
+        includes: List of include folders for the test build
+
+    Returns:
+        Configuration dict for ESPHome
+    """
+    return {
+        "esphome": {
+            "name": config_name,
+            "friendly_name": "CPP Unit Tests",
+            "libraries": PLATFORMIO_GOOGLE_TEST_LIB,
+            "platformio_options": {
+                "build_type": "debug",
+                "build_unflags": [
+                    "-Os",  # remove size-opt flag
+                ],
+                "build_flags": [
+                    "-Og",  # optimize for debug
+                ],
+                "debug_build_flags": [  # only for debug builds
+                    "-g3",  # max debug info
+                    "-ggdb3",
+                ],
+            },
+            "includes": includes,
+        },
+        "host": {},
+        "logger": {"level": "DEBUG"},
+    }
+
+
+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
+
+    # Remove components that do not have tests
+    components = filter_components_without_tests(selected_components)
+
+    if len(components) == 0:
+        print(
+            "No components specified or no tests found for the specified components.",
+            file=sys.stderr,
+        )
+        return 0
+
+    components = sorted(components)
+
+    # Obtain possible dependencies for the requested components:
+    components_with_dependencies = sorted(get_all_dependencies(set(components)))
+
+    # Build a list of include folders, one folder per component containing tests.
+    # A special replacement main.cpp is located in /tests/components/main.cpp
+    includes: list[str] = ["main.cpp"] + 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)
+
+    CORE.config_path = COMPONENTS_TESTS_DIR / "dummy.yaml"
+    CORE.dashboard = None
+
+    # 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.
+    config.update({key: {} for key in components_with_dependencies})
+
+    print(f"Testing components: {', '.join(components)}")
+    CORE.config = config
+    args = parse_args(["program", "compile", str(CORE.config_path)])
+    try:
+        exit_code: int = command_compile(args, config)
+
+        if exit_code != 0:
+            print(f"Error compiling unit tests for {', '.join(components)}")
+            return exit_code
+    except Exception as e:
+        print(
+            f"Error compiling unit tests for {', '.join(components)}. Check path. : {e}"
+        )
+        return 2
+
+    # After a successful compilation, locate the executable and run it:
+    idedata = get_idedata(config)
+    if idedata is None:
+        print("Cannot find executable")
+        return 1
+
+    program_path: str = idedata.raw["prog_path"]
+    run_cmd: list[str] = [program_path]
+    run_proc = subprocess.run(run_cmd, check=False)
+    return run_proc.returncode
+
+
+def main() -> None:
+    parser = argparse.ArgumentParser(
+        description="Run C++ unit tests for ESPHome components."
+    )
+    parser.add_argument(
+        "components",
+        nargs="*",
+        help="List of components to test. Use --all to test all known components.",
+    )
+    parser.add_argument("--all", action="store_true", help="Test all known components.")
+
+    args = parser.parse_args()
+
+    if args.all:
+        components: list[str] = get_all_components()
+    else:
+        components: list[str] = args.components
+
+    sys.exit(run_tests(components))
+
+
+if __name__ == "__main__":
+    main()

script/determine-jobs.py

@@ -52,13 +52,16 @@ from helpers import (
     CPP_FILE_EXTENSIONS,
     PYTHON_FILE_EXTENSIONS,
     changed_files,
-    filter_component_files,
+    core_changed,
+    filter_component_and_test_cpp_files,
+    filter_component_and_test_files,
     get_all_dependencies,
     get_changed_components,
     get_component_from_path,
     get_component_test_files,
     get_components_from_integration_fixtures,
     get_components_with_dependencies,
+    get_cpp_changed_components,
     git_ls_files,
     parse_test_filename,
     root_path,
@@ -143,9 +146,8 @@ def should_run_integration_tests(branch: str | None = None) -> bool:
     """
     files = changed_files(branch)
 
-    # Check if any core files changed (esphome/core/*)
-    for file in files:
-        if file.startswith("esphome/core/"):
+    if core_changed(files):
+        # If any core files changed, run integration tests
         return True
 
     # Check if any integration test files changed
@@ -283,6 +285,40 @@ def should_run_python_linters(branch: str | None = None) -> bool:
     return _any_changed_file_endswith(branch, PYTHON_FILE_EXTENSIONS)
 
 
+def determine_cpp_unit_tests(
+    branch: str | None = None,
+) -> tuple[bool, list[str]]:
+    """Determine if C++ unit tests should run based on changed files.
+
+    This function is used by the CI workflow to skip C++ unit tests when
+    no relevant files have changed, saving CI time and resources.
+
+    C++ unit tests will run when any of the following conditions are met:
+
+    1. Any C++ core source files changed (esphome/core/*), in which case
+       all cpp unit tests run.
+    2. A test file for a component changed, which triggers tests for that
+       component.
+    3. The code for a component changed, which triggers tests for that
+       component and all components that depend on it.
+
+    Args:
+        branch: Branch to compare against. If None, uses default.
+
+    Returns:
+        Tuple of (run_all, components) where:
+        - run_all: True if all tests should run, False otherwise
+        - components: List of specific components to test (empty if run_all)
+    """
+    files = changed_files(branch)
+    if core_changed(files):
+        return (True, [])
+
+    # Filter to only C++ files
+    cpp_files = list(filter(filter_component_and_test_cpp_files, files))
+    return (False, get_cpp_changed_components(cpp_files))
+
+
 def _any_changed_file_endswith(branch: str | None, extensions: tuple[str, ...]) -> bool:
     """Check if a changed file ends with any of the specified extensions."""
     return any(file.endswith(extensions) for file in changed_files(branch))
@@ -579,7 +615,7 @@ def main() -> None:
     else:
         # Get both directly changed and all changed (with dependencies)
         changed = changed_files(args.branch)
-        component_files = [f for f in changed if filter_component_files(f)]
+        component_files = [f for f in changed if filter_component_and_test_files(f)]
 
         directly_changed_components = get_components_with_dependencies(
             component_files, False
@@ -646,6 +682,9 @@ def main() -> None:
         files_to_check_count = 0
 
     # Build output
+    # Determine which C++ unit tests to run
+    cpp_run_all, cpp_components = determine_cpp_unit_tests(args.branch)
+
     output: dict[str, Any] = {
         "integration_tests": run_integration,
         "clang_tidy": run_clang_tidy,
@@ -661,6 +700,8 @@ def main() -> None:
         "dependency_only_count": len(dependency_only_components),
         "changed_cpp_file_count": changed_cpp_file_count,
         "memory_impact": memory_impact,
+        "cpp_unit_tests_run_all": cpp_run_all,
+        "cpp_unit_tests_components": cpp_components,
     }
 
     # Output as JSON

script/extract_automations.py

@@ -2,19 +2,14 @@
 
 import json
 
-from helpers import git_ls_files
+from helpers import get_all_component_files, get_components_with_dependencies
 
 from esphome.automation import ACTION_REGISTRY, CONDITION_REGISTRY
 from esphome.pins import PIN_SCHEMA_REGISTRY
 
-list_components = __import__("list-components")
-
-
 if __name__ == "__main__":
-    files = git_ls_files()
-    files = filter(list_components.filter_component_files, files)
-
-    components = list_components.get_components(files, True)
+    files = get_all_component_files()
+    components = get_components_with_dependencies(files, True)
 
     dump = {
         "actions": sorted(list(ACTION_REGISTRY.keys())),

script/helpers.py

@@ -25,12 +25,21 @@ CPP_FILE_EXTENSIONS = (".cpp", ".h", ".hpp", ".cc", ".cxx", ".c", ".tcc")
 # Python file extensions
 PYTHON_FILE_EXTENSIONS = (".py", ".pyi")
 
+# Combined C++ and Python file extensions for convenience
+CPP_AND_PYTHON_FILE_EXTENSIONS = (*CPP_FILE_EXTENSIONS, *PYTHON_FILE_EXTENSIONS)
+
 # YAML file extensions
 YAML_FILE_EXTENSIONS = (".yaml", ".yml")
 
 # Component path prefix
 ESPHOME_COMPONENTS_PATH = "esphome/components/"
 
+# Test components path prefix
+ESPHOME_TESTS_COMPONENTS_PATH = "tests/components/"
+
+# Tuple of component and test paths for efficient startswith checks
+COMPONENT_AND_TESTS_PATHS = (ESPHOME_COMPONENTS_PATH, ESPHOME_TESTS_COMPONENTS_PATH)
+
 # Base bus components - these ARE the bus implementations and should not
 # be flagged as needing migration since they are the platform/base components
 BASE_BUS_COMPONENTS = {
@@ -658,17 +667,32 @@ def get_components_from_integration_fixtures() -> set[str]:
     return components
 
 
-def filter_component_files(file_path: str) -> bool:
-    """Check if a file path is a component file.
+def filter_component_and_test_files(file_path: str) -> bool:
+    """Check if a file path is a component or test file.
 
     Args:
         file_path: Path to check
 
     Returns:
-        True if the file is in a component directory
+        True if the file is in a component or test directory
     """
-    return file_path.startswith("esphome/components/") or file_path.startswith(
-        "tests/components/"
+    return file_path.startswith(COMPONENT_AND_TESTS_PATHS) or (
+        file_path.startswith(ESPHOME_TESTS_COMPONENTS_PATH)
+        and file_path.endswith(YAML_FILE_EXTENSIONS)
+    )
+
+
+def filter_component_and_test_cpp_files(file_path: str) -> bool:
+    """Check if a file is a C++ source file in component or test directories.
+
+    Args:
+        file_path: Path to check
+
+    Returns:
+        True if the file is a C++ source/header file in component or test directories
+    """
+    return file_path.endswith(CPP_FILE_EXTENSIONS) and file_path.startswith(
+        COMPONENT_AND_TESTS_PATHS
     )
 
 
@@ -740,7 +764,7 @@ def create_components_graph() -> dict[str, list[str]]:
 
     # The root directory of the repo
     root = Path(__file__).parent.parent
-    components_dir = root / "esphome" / "components"
+    components_dir = root / ESPHOME_COMPONENTS_PATH
     # Fake some directory so that get_component works
     CORE.config_path = root
     # Various configuration to capture different outcomes used by `AUTO_LOAD` function.
@@ -873,3 +897,81 @@ def get_components_with_dependencies(
         return sorted(all_changed_components)
 
     return sorted(components)
+
+
+def get_all_component_files() -> list[str]:
+    """Get all component and test files from git.
+
+    Returns:
+        List of all component and test file paths
+    """
+    files = git_ls_files()
+    return list(filter(filter_component_and_test_files, files))
+
+
+def get_all_components() -> list[str]:
+    """Get all component names.
+
+    This function uses git to find all component files and extracts the component names.
+    It returns the same list as calling list-components.py without arguments.
+
+    Returns:
+        List of all component names
+    """
+    return get_components_with_dependencies(get_all_component_files(), False)
+
+
+def core_changed(files: list[str]) -> bool:
+    """Check if any core C++ or Python files have changed.
+
+    Args:
+        files: List of file paths to check
+
+    Returns:
+        True if any core C++ or Python files have changed
+    """
+    return any(
+        f.startswith("esphome/core/") and f.endswith(CPP_AND_PYTHON_FILE_EXTENSIONS)
+        for f in files
+    )
+
+
+def get_cpp_changed_components(files: list[str]) -> list[str]:
+    """Get components that have changed C++ files or tests.
+
+    This function analyzes a list of changed files and determines which components
+    are affected. It handles two scenarios:
+
+    1. Test files changed (tests/components/<component>/*.cpp):
+       - Adds the component to the affected list
+       - Only that component needs to be tested
+
+    2. Component C++ files changed (esphome/components/<component>/*):
+       - Adds the component to the affected list
+       - Also adds all components that depend on this component (recursively)
+       - This ensures that changes propagate to dependent components
+
+    Args:
+        files: List of file paths to analyze (should be C++ files)
+
+    Returns:
+        Sorted list of component names that need C++ unit tests run
+    """
+    components_graph = create_components_graph()
+    affected: set[str] = set()
+    for file in files:
+        if not file.endswith(CPP_FILE_EXTENSIONS):
+            continue
+        if file.startswith(ESPHOME_TESTS_COMPONENTS_PATH):
+            parts = file.split("/")
+            if len(parts) >= 4:
+                component_dir = Path(ESPHOME_TESTS_COMPONENTS_PATH) / parts[2]
+                if component_dir.is_dir():
+                    affected.add(parts[2])
+        elif file.startswith(ESPHOME_COMPONENTS_PATH):
+            parts = file.split("/")
+            if len(parts) >= 4:
+                component = parts[2]
+                affected.update(find_children_of_component(components_graph, component))
+                affected.add(component)
+    return sorted(affected)

script/list-components.py

@@ -3,18 +3,14 @@ import argparse
 
 from helpers import (
     changed_files,
-    filter_component_files,
+    filter_component_and_test_cpp_files,
+    filter_component_and_test_files,
+    get_all_component_files,
     get_components_with_dependencies,
-    git_ls_files,
+    get_cpp_changed_components,
 )
 
 
-def get_all_component_files() -> list[str]:
-    """Get all component files from git."""
-    files = git_ls_files()
-    return list(filter(filter_component_files, files))
-
-
 def main():
     parser = argparse.ArgumentParser()
     parser.add_argument(
@@ -39,16 +35,29 @@ def main():
     parser.add_argument(
         "-b", "--branch", help="Branch to compare changed files against"
     )
+    parser.add_argument(
+        "--cpp-changed",
+        action="store_true",
+        help="List components with changed C++ files",
+    )
     args = parser.parse_args()
 
     if args.branch and not (
-        args.changed or args.changed_direct or args.changed_with_deps
+        args.changed
+        or args.changed_direct
+        or args.changed_with_deps
+        or args.cpp_changed
     ):
         parser.error(
-            "--branch requires --changed, --changed-direct, or --changed-with-deps"
+            "--branch requires --changed, --changed-direct, --changed-with-deps, or --cpp-changed"
         )
 
-    if args.changed or args.changed_direct or args.changed_with_deps:
+    if (
+        args.changed
+        or args.changed_direct
+        or args.changed_with_deps
+        or args.cpp_changed
+    ):
         # When --changed* is passed, only get the changed files
         changed = changed_files(args.branch)
 
@@ -68,6 +77,11 @@ def main():
         # - --changed-with-deps: Used by CI test determination (script/determine-jobs.py)
         #   Returns: Components with code changes + their dependencies (not infrastructure)
         #   Reason: CI needs to test changed components and their dependents
+        #
+        # - --cpp-changed: Used by CI to determine if any C++ files changed (script/determine-jobs.py)
+        #   Returns: Only components with changed C++ files
+        #   Reason: Only components with C++ changes need C++ testing
+
         base_test_changed = any(
             "tests/test_build_components" in file for file in changed
         )
@@ -80,7 +94,7 @@ def main():
             # Only look at changed component files (ignore infrastructure changes)
             # For --changed-direct: only actual component code changes matter (for isolation)
             # For --changed-with-deps: only actual component code changes matter (for testing)
-            files = [f for f in changed if filter_component_files(f)]
+            files = [f for f in changed if filter_component_and_test_files(f)]
     else:
         # Get all component files
         files = get_all_component_files()
@@ -100,6 +114,11 @@ def main():
         # Return only directly changed components (without dependencies)
         for c in get_components_with_dependencies(files, False):
             print(c)
+    elif args.cpp_changed:
+        # Only look at changed cpp files
+        files = list(filter(filter_component_and_test_cpp_files, changed))
+        for c in get_cpp_changed_components(files):
+            print(c)
     else:
         # Return all changed components (with dependencies) - default behavior
         for c in get_components_with_dependencies(files, args.changed):

tests/components/.gitignore

@@ -0,0 +1,5 @@
+# Gitignore settings for ESPHome
+# This is an example and may include too much for your use-case.
+# You can modify this file to suit your needs.
+/.esphome/
+/secrets.yaml

tests/components/README.md

@@ -0,0 +1,32 @@
+# How to write C++ ESPHome unit tests
+
+1. Locate the folder with your component or create a new one with the same name as the component.
+2. Write the tests. You can add as many `.cpp` and `.h` files as you need to organize your tests.
+
+**IMPORTANT**: wrap all your testing code in a unique namespace to avoid linker collisions when compiling
+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`.
+
+
+## Running component unit tests
+
+(from the repository root)
+```bash
+./script/cpp_unit_test.py component1 component2 ...
+```
+
+The above will compile and run the provided components and their tests.
+
+To run all tests, you can invoke `cpp_unit_test.py` with the special `--all` flag:
+
+```bash
+./script/cpp_unit_test.py --all
+```
+
+To run a specific test suite, you can provide a Google Test filter:
+
+```bash
+GTEST_FILTER='UART*' ./script/cpp_unit_test.py uart modbus
+```
+
+The process will return `0` for success or nonzero for failure. In case of failure, the errors will be printed out to the console.

tests/components/main.cpp

@@ -0,0 +1,26 @@
+#include <gtest/gtest.h>
+
+/*
+This special main.cpp replaces the default one.
+It will run all the Google Tests found in all compiled cpp files and then exit with the result
+See README.md for more information
+*/
+
+// Auto generated code by esphome
+// ========== AUTO GENERATED INCLUDE BLOCK BEGIN ===========
+// ========== AUTO GENERATED INCLUDE BLOCK END ==========="
+
+void original_setup() {
+  // This function won't be run.
+
+  // ========== AUTO GENERATED CODE BEGIN ===========
+  // =========== AUTO GENERATED CODE END ============
+}
+
+void setup() {
+  ::testing::InitGoogleTest();
+  int exit_code = RUN_ALL_TESTS();
+  exit(exit_code);
+}
+
+void loop() {}

tests/components/uart/common.h

@@ -0,0 +1,37 @@
+#pragma once
+#include <vector>
+#include <cstdint>
+#include <cstring>
+#include <gmock/gmock.h>
+#include <gtest/gtest.h>
+#include "esphome/components/uart/uart_component.h"
+
+namespace esphome::uart::testing {
+
+using ::testing::_;
+using ::testing::Return;
+using ::testing::SaveArg;
+using ::testing::DoAll;
+using ::testing::Invoke;
+using ::testing::SetArgPointee;
+
+// Derive a mock from UARTComponent to test the wrapper implementations.
+class MockUARTComponent : public UARTComponent {
+ public:
+  using UARTComponent::write_array;
+  using UARTComponent::write_byte;
+
+  // NOTE: std::vector is used here for test convenience. For production code,
+  // consider using StaticVector or FixedVector from esphome/core/helpers.h instead.
+  std::vector<uint8_t> written_data;
+
+  void write_array(const uint8_t *data, size_t len) override { written_data.assign(data, data + len); }
+
+  MOCK_METHOD(bool, read_array, (uint8_t * data, size_t len), (override));
+  MOCK_METHOD(bool, peek_byte, (uint8_t * data), (override));
+  MOCK_METHOD(int, available, (), (override));
+  MOCK_METHOD(void, flush, (), (override));
+  MOCK_METHOD(void, check_logger_conflict, (), (override));
+};
+
+}  // namespace esphome::uart::testing

tests/components/uart/uart_component.cpp

@@ -0,0 +1,73 @@
+#include "common.h"
+
+namespace esphome::uart::testing {
+
+TEST(UARTComponentTest, SetGetBaudRate) {
+  MockUARTComponent mock;
+  mock.set_baud_rate(38400);
+  EXPECT_EQ(mock.get_baud_rate(), 38400);
+}
+
+TEST(UARTComponentTest, SetGetStopBits) {
+  MockUARTComponent mock;
+  mock.set_stop_bits(2);
+  EXPECT_EQ(mock.get_stop_bits(), 2);
+}
+
+TEST(UARTComponentTest, SetGetDataBits) {
+  MockUARTComponent mock;
+  mock.set_data_bits(7);
+  EXPECT_EQ(mock.get_data_bits(), 7);
+}
+
+TEST(UARTComponentTest, SetGetParity) {
+  MockUARTComponent mock;
+  mock.set_parity(UARTParityOptions::UART_CONFIG_PARITY_EVEN);
+  EXPECT_EQ(mock.get_parity(), UARTParityOptions::UART_CONFIG_PARITY_EVEN);
+}
+
+TEST(UARTComponentTest, SetGetRxBufferSize) {
+  MockUARTComponent mock;
+  mock.set_rx_buffer_size(128);
+  EXPECT_EQ(mock.get_rx_buffer_size(), 128);
+}
+
+TEST(UARTComponentTest, WriteArrayVector) {
+  MockUARTComponent mock;
+  std::vector<uint8_t> data = {10, 20, 30};
+  mock.write_array(data);
+  EXPECT_EQ(mock.written_data, data);
+}
+TEST(UARTComponentTest, WriteByte) {
+  MockUARTComponent mock;
+  uint8_t byte = 0x79;
+  mock.write_byte(byte);
+  EXPECT_EQ(mock.written_data.size(), 1);
+  EXPECT_EQ(mock.written_data[0], byte);
+}
+
+TEST(UARTComponentTest, WriteStr) {
+  MockUARTComponent mock;
+  const char *str = "Hello";
+  std::vector<uint8_t> captured;
+  mock.write_str(str);
+  EXPECT_EQ(mock.written_data.size(), strlen(str));
+  EXPECT_EQ(0, strncmp(str, (const char *) mock.written_data.data(), mock.written_data.size()));
+}
+
+// Tests for wrapper methods forwarding to pure virtual read_array
+TEST(UARTComponentTest, ReadByteSuccess) {
+  MockUARTComponent mock;
+  uint8_t value = 0;
+  EXPECT_CALL(mock, read_array(&value, 1)).WillOnce(Return(true));
+  EXPECT_TRUE(mock.read_byte(&value));
+}
+
+TEST(UARTComponentTest, ReadByteFailure) {
+  MockUARTComponent mock;
+  uint8_t value = 0xFF;
+  EXPECT_CALL(mock, read_array(&value, 1)).WillOnce(Return(false));
+  EXPECT_FALSE(mock.read_byte(&value));
+}
+
+}  // namespace esphome::uart::testing

tests/components/uart/uart_device.cpp

@@ -0,0 +1,108 @@
+#include "common.h"
+#include "esphome/components/uart/uart.h"
+
+namespace esphome::uart::testing {
+
+TEST(UARTDeviceTest, ReadByteSuccess) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  uint8_t value = 0;
+  EXPECT_CALL(mock, read_array(_, 1)).WillOnce(DoAll(SetArgPointee<0>(0x5A), Return(true)));
+  bool result = dev.read_byte(&value);
+  EXPECT_TRUE(result);
+  EXPECT_EQ(value, 0x5A);
+}
+
+TEST(UARTDeviceTest, ReadByteFailure) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  uint8_t value = 0xFF;
+  EXPECT_CALL(mock, read_array(_, 1)).WillOnce(Return(false));
+  bool result = dev.read_byte(&value);
+  EXPECT_FALSE(result);
+}
+
+TEST(UARTDeviceTest, PeekByteSuccess) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  uint8_t value = 0;
+  EXPECT_CALL(mock, peek_byte(_)).WillOnce(DoAll(SetArgPointee<0>(0xA5), Return(true)));
+  bool result = dev.peek_byte(&value);
+  EXPECT_TRUE(result);
+  EXPECT_EQ(value, 0xA5);
+}
+
+TEST(UARTDeviceTest, PeekByteFailure) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  uint8_t value = 0;
+  EXPECT_CALL(mock, peek_byte(_)).WillOnce(Return(false));
+  bool result = dev.peek_byte(&value);
+  EXPECT_FALSE(result);
+}
+
+TEST(UARTDeviceTest, Available) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  EXPECT_CALL(mock, available()).WillOnce(Return(5));
+  EXPECT_EQ(dev.available(), 5);
+}
+
+TEST(UARTDeviceTest, FlushCallsParent) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  EXPECT_CALL(mock, flush()).Times(1);
+  dev.flush();
+}
+
+TEST(UARTDeviceTest, WriteByteForwardsToWriteArray) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  dev.write_byte(0xAB);
+  EXPECT_EQ(mock.written_data.size(), 1);
+  EXPECT_EQ(mock.written_data[0], 0xAB);
+}
+TEST(UARTDeviceTest, WriteArrayPointer) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  uint8_t data[3] = {1, 2, 3};
+  dev.write_array(data, 3);
+  EXPECT_EQ(mock.written_data.size(), 3);
+  EXPECT_EQ(mock.written_data, std::vector(data, data + 3));
+}
+
+TEST(UARTDeviceTest, WriteArrayVector) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  std::vector<uint8_t> data = {4, 5, 6};
+  dev.write_array(data);
+  EXPECT_EQ(mock.written_data, data);
+}
+
+TEST(UARTDeviceTest, WriteArrayStdArray) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  std::array<uint8_t, 4> data = {7, 8, 9, 10};
+  dev.write_array(data);
+  EXPECT_EQ(mock.written_data.size(), data.size());
+  EXPECT_EQ(mock.written_data, std::vector(data.begin(), data.end()));
+}
+
+TEST(UARTDeviceTest, WriteStrForwardsToWriteArray) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  const char *str = "ESPHome";
+  dev.write_str(str);
+  EXPECT_EQ(mock.written_data.size(), strlen(str));
+  EXPECT_EQ(0, strncmp(str, (const char *) mock.written_data.data(), mock.written_data.size()));
+}
+
+TEST(UARTDeviceTest, WriteStrEmptyString) {
+  MockUARTComponent mock;
+  UARTDevice dev(&mock);
+  const char *str = "";
+  dev.write_str(str);
+  EXPECT_EQ(mock.written_data.size(), 0);
+}
+
+}  // namespace esphome::uart::testing

tests/script/test_determine_jobs.py

@@ -5,7 +5,6 @@ import importlib.util
 import json
 import os
 from pathlib import Path
-import subprocess
 import sys
 from unittest.mock import Mock, call, patch
 
@@ -56,9 +55,9 @@ def mock_should_run_python_linters() -> Generator[Mock, None, None]:
 
 
 @pytest.fixture
-def mock_subprocess_run() -> Generator[Mock, None, None]:
-    """Mock subprocess.run for list-components.py calls."""
-    with patch.object(determine_jobs.subprocess, "run") as mock:
+def mock_determine_cpp_unit_tests() -> Generator[Mock, None, None]:
+    """Mock determine_cpp_unit_tests from helpers."""
+    with patch.object(determine_jobs, "determine_cpp_unit_tests") as mock:
         yield mock
 
 
@@ -82,8 +81,8 @@ def test_main_all_tests_should_run(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
+    mock_determine_cpp_unit_tests: Mock,
     capsys: pytest.CaptureFixture[str],
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
@@ -95,6 +94,7 @@ def test_main_all_tests_should_run(
     mock_should_run_clang_tidy.return_value = True
     mock_should_run_clang_format.return_value = True
     mock_should_run_python_linters.return_value = True
+    mock_determine_cpp_unit_tests.return_value = (False, ["wifi", "api", "sensor"])
 
     # Mock changed_files to return non-component files (to avoid memory impact)
     # Memory impact only runs when component C++ files change
@@ -114,15 +114,15 @@ def test_main_all_tests_should_run(
         ),
         patch.object(
             determine_jobs,
-            "filter_component_files",
+            "filter_component_and_test_files",
             side_effect=lambda f: f.startswith("esphome/components/"),
         ),
         patch.object(
             determine_jobs,
             "get_components_with_dependencies",
-            side_effect=lambda files, deps: ["wifi", "api"]
-            if not deps
-            else ["wifi", "api", "sensor"],
+            side_effect=lambda files, deps: (
+                ["wifi", "api"] if not deps else ["wifi", "api", "sensor"]
+            ),
         ),
     ):
         determine_jobs.main()
@@ -150,6 +150,8 @@ def test_main_all_tests_should_run(
     # memory_impact should be false (no component C++ files changed)
     assert "memory_impact" in output
     assert output["memory_impact"]["should_run"] == "false"
+    assert output["cpp_unit_tests_run_all"] is False
+    assert output["cpp_unit_tests_components"] == ["wifi", "api", "sensor"]
 
 
 def test_main_no_tests_should_run(
@@ -157,8 +159,8 @@ def test_main_no_tests_should_run(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
+    mock_determine_cpp_unit_tests: Mock,
     capsys: pytest.CaptureFixture[str],
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
@@ -170,6 +172,7 @@ def test_main_no_tests_should_run(
     mock_should_run_clang_tidy.return_value = False
     mock_should_run_clang_format.return_value = False
     mock_should_run_python_linters.return_value = False
+    mock_determine_cpp_unit_tests.return_value = (False, [])
 
     # Mock changed_files to return no component files
     mock_changed_files.return_value = []
@@ -178,7 +181,9 @@ def test_main_no_tests_should_run(
     with (
         patch("sys.argv", ["determine-jobs.py"]),
         patch.object(determine_jobs, "get_changed_components", return_value=[]),
-        patch.object(determine_jobs, "filter_component_files", return_value=False),
+        patch.object(
+            determine_jobs, "filter_component_and_test_files", return_value=False
+        ),
         patch.object(
             determine_jobs, "get_components_with_dependencies", return_value=[]
         ),
@@ -202,31 +207,8 @@ def test_main_no_tests_should_run(
     # memory_impact should be present
     assert "memory_impact" in output
     assert output["memory_impact"]["should_run"] == "false"
-
-
-def test_main_list_components_fails(
-    mock_should_run_integration_tests: Mock,
-    mock_should_run_clang_tidy: Mock,
-    mock_should_run_clang_format: Mock,
-    mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
-    capsys: pytest.CaptureFixture[str],
-) -> None:
-    """Test when list-components.py fails."""
-    mock_should_run_integration_tests.return_value = True
-    mock_should_run_clang_tidy.return_value = True
-    mock_should_run_clang_format.return_value = True
-    mock_should_run_python_linters.return_value = True
-
-    # Mock list-components.py failure
-    mock_subprocess_run.side_effect = subprocess.CalledProcessError(1, "cmd")
-
-    # Run main function with mocked argv - should raise
-    with (
-        patch("sys.argv", ["determine-jobs.py"]),
-        pytest.raises(subprocess.CalledProcessError),
-    ):
-        determine_jobs.main()
+    assert output["cpp_unit_tests_run_all"] is False
+    assert output["cpp_unit_tests_components"] == []
 
 
 def test_main_with_branch_argument(
@@ -234,8 +216,8 @@ def test_main_with_branch_argument(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
+    mock_determine_cpp_unit_tests: Mock,
     capsys: pytest.CaptureFixture[str],
     monkeypatch: pytest.MonkeyPatch,
 ) -> None:
@@ -247,6 +229,7 @@ def test_main_with_branch_argument(
     mock_should_run_clang_tidy.return_value = True
     mock_should_run_clang_format.return_value = False
     mock_should_run_python_linters.return_value = True
+    mock_determine_cpp_unit_tests.return_value = (False, ["mqtt"])
 
     # Mock changed_files to return non-component files (to avoid memory impact)
     # Memory impact only runs when component C++ files change
@@ -258,7 +241,7 @@ def test_main_with_branch_argument(
         patch.object(determine_jobs, "get_changed_components", return_value=["mqtt"]),
         patch.object(
             determine_jobs,
-            "filter_component_files",
+            "filter_component_and_test_files",
             side_effect=lambda f: f.startswith("esphome/components/"),
         ),
         patch.object(
@@ -296,6 +279,8 @@ def test_main_with_branch_argument(
     # memory_impact should be false (no component C++ files changed)
     assert "memory_impact" in output
     assert output["memory_impact"]["should_run"] == "false"
+    assert output["cpp_unit_tests_run_all"] is False
+    assert output["cpp_unit_tests_components"] == ["mqtt"]
 
 
 def test_should_run_integration_tests(
@@ -506,7 +491,6 @@ def test_main_filters_components_without_tests(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
     capsys: pytest.CaptureFixture[str],
     tmp_path: Path,
@@ -556,16 +540,17 @@ def test_main_filters_components_without_tests(
         ),
         patch.object(
             determine_jobs,
-            "filter_component_files",
+            "filter_component_and_test_files",
             side_effect=lambda f: f.startswith("esphome/components/"),
         ),
         patch.object(
             determine_jobs,
             "get_components_with_dependencies",
-            side_effect=lambda files, deps: ["wifi", "sensor"]
-            if not deps
-            else ["wifi", "sensor", "airthings_ble"],
+            side_effect=lambda files, deps: (
+                ["wifi", "sensor"] if not deps else ["wifi", "sensor", "airthings_ble"]
             ),
+        ),
+        patch.object(determine_jobs, "changed_files", return_value=[]),
     ):
         # Clear the cache since we're mocking root_path
         determine_jobs._component_has_tests.cache_clear()
@@ -808,7 +793,6 @@ def test_clang_tidy_mode_full_scan(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
     capsys: pytest.CaptureFixture[str],
     monkeypatch: pytest.MonkeyPatch,
@@ -829,7 +813,9 @@ def test_clang_tidy_mode_full_scan(
         patch("sys.argv", ["determine-jobs.py"]),
         patch.object(determine_jobs, "_is_clang_tidy_full_scan", return_value=True),
         patch.object(determine_jobs, "get_changed_components", return_value=[]),
-        patch.object(determine_jobs, "filter_component_files", return_value=False),
+        patch.object(
+            determine_jobs, "filter_component_and_test_files", return_value=False
+        ),
         patch.object(
             determine_jobs, "get_components_with_dependencies", return_value=[]
         ),
@@ -873,7 +859,6 @@ def test_clang_tidy_mode_targeted_scan(
     mock_should_run_clang_tidy: Mock,
     mock_should_run_clang_format: Mock,
     mock_should_run_python_linters: Mock,
-    mock_subprocess_run: Mock,
     mock_changed_files: Mock,
     capsys: pytest.CaptureFixture[str],
     monkeypatch: pytest.MonkeyPatch,
@@ -912,7 +897,7 @@ def test_clang_tidy_mode_targeted_scan(
         patch.object(determine_jobs, "get_changed_components", return_value=components),
         patch.object(
             determine_jobs,
-            "filter_component_files",
+            "filter_component_and_test_files",
             side_effect=lambda f: f.startswith("esphome/components/"),
         ),
         patch.object(