[Nexthop] Add CMake test infrastructure for FBOSS Image Builder

Integrate distro_cli Python unit tests into the FBOSS CMake build system to enable automated testing in CI/CD pipelines.

- Add FbossImageDistroCliTests.cmake to discover and register Python unit tests
- Configure test discovery for distro_cli modules (builder, cmds, lib, tools)
- Update root CMakeLists.txt to include distro_cli test suite
- Enable distro_cli tests in GitHub Actions workflow
- Update distro_cli README with build and test instructions

The CMake configuration automatically discovers all *_test.py files and registers them as CTest targets, allowing tests to run via 'ctest' or 'make test'.

Author: raghav-nexthop

CMakeLists.txt

@@ -1154,3 +1154,6 @@ if (GITHUB_ACTIONS_BUILD)
     fsdb_all_services
   )
 endif()
+
+# FBOSS Image Builder distro_cli tests
+include(cmake/FbossImageDistroCliTests.cmake)

cmake/FbossImageDistroCliTests.cmake

@@ -0,0 +1,36 @@
+# CMake to build and test fboss-image/distro_cli
+
+# In general, libraries and binaries in fboss/foo/bar are built by
+# cmake/FooBar.cmake
+
+include(FBPythonBinary)
+
+file(GLOB DISTRO_CLI_TEST_SOURCES
+  "fboss-image/distro_cli/tests/*_test.py"
+)
+
+file(GLOB DISTRO_CLI_TEST_HELPERS
+  "fboss-image/distro_cli/tests/test_helpers.py"
+)
+
+file(GLOB_RECURSE DISTRO_CLI_LIB_SOURCES
+  "fboss-image/distro_cli/builder/*.py"
+  "fboss-image/distro_cli/cmds/*.py"
+  "fboss-image/distro_cli/lib/*.py"
+  "fboss-image/distro_cli/tools/*.py"
+)
+
+file(COPY "fboss-image/distro_cli/tests/data" DESTINATION "${CMAKE_CURRENT_BINARY_DIR}/fboss-image/distro_cli/tests")
+
+add_fb_python_unittest(
+  distro_cli_tests
+  BASE_DIR "fboss-image"
+  SOURCES
+    ${DISTRO_CLI_TEST_SOURCES}
+    ${DISTRO_CLI_TEST_HELPERS}
+    ${DISTRO_CLI_LIB_SOURCES}
+  ENV
+    "PYTHONPATH=${CMAKE_CURRENT_SOURCE_DIR}/fboss-image/distro_cli"
+)
+
+install_fb_python_executable(distro_cli_tests)

fboss-image/distro_cli/README.md

@@ -110,20 +110,56 @@ Components are built in the following order:
 
 ### Running Tests
 
+#### With Bazel (Recommended)
+
 ```bash
 # Run all tests
-cd fboss-image/distro_cli
-python3 -m unittest discover -s tests -p '*_test.py'
+bazel test //fboss/fboss-image/distro_cli:all
 
 # Run specific test
-python3 -m unittest tests.cli_test
+bazel test //fboss/fboss-image/distro_cli:cli_test
+
+# Run with detailed output
+bazel test //fboss/fboss-image/distro_cli:all --test_output=all
+```
+
+#### With pytest
+
+```bash
+# Run all tests (from fboss-image directory)
+cd fboss-image
+PYTHONPATH=. python3 -m pytest distro_cli/tests/ -v
+
+# Run specific test file
+PYTHONPATH=. python3 -m pytest distro_cli/tests/cli_test.py -v
+
+# Run specific test class or method
+PYTHONPATH=. python3 -m pytest distro_cli/tests/cli_test.py::CLITest::test_cli_creation -v
+```
+
+#### With unittest
+
+```bash
+# Run all tests (from fboss-image directory)
+cd fboss-image
+PYTHONPATH=. python3 -m unittest discover -s distro_cli/tests -p '*_test.py'
+
+# Run specific test module
+PYTHONPATH=. python3 -m unittest distro_cli.tests.cli_test
+
+# Run specific test class
+PYTHONPATH=. python3 -m unittest distro_cli.tests.cli_test.CLITest
 ```
 
 ### Linting
 
 ```bash
+# With ruff (from distro_cli directory)
 cd fboss-image/distro_cli
 python3 -m ruff check .
+
+# With bazel (from repository root)
+bazel test //private-fboss/fboss-image/distro_cli:lint_check
 ```
 
 ### Project Structure
@@ -152,7 +188,7 @@ fboss-image/distro_cli/
 The CLI uses a custom OOP wrapper around argparse (stdlib only, no external dependencies):
 
 ```python
-from lib.cli import CLI
+from distro_cli.lib.cli import CLI
 
 # Create CLI
 cli = CLI(description='My CLI')
@@ -171,3 +207,27 @@ device.add_command('ssh', ssh_func, help_text='SSH to device')
 # Run
 cli.run(setup_logging_func=setup_logging)
 ```
+
+## Running Tests
+
+### Quick Tests (Default)
+Run all fast unit tests (excludes long-running E2E tests):
+```bash
+python3 -m pytest distro_cli/tests/ -v
+# or explicitly exclude e2e tests:
+python3 -m pytest distro_cli/tests/ -m "not e2e" -v
+```
+
+### E2E Tests Only
+Run only the end-to-end tests (kernel build, SAI build):
+```bash
+python3 -m pytest distro_cli/tests/ -m e2e -v -s
+```
+
+### All Tests (Including E2E)
+Run everything:
+```bash
+python3 -m pytest distro_cli/tests/ -v -s
+```
+
+**Note:** E2E tests can take 10-60 minutes and require actual source files (kernel sources, SAI SDK, etc.).