test(posix): add Windows shim header and runtime coverage

Wire up gtest-based unit tests for the Windows POSIX shim layer using
px4_add_unit_gtest. Adds two test translation units that exercise the
inline header functions (libgen, dirent, sched, syslog, mman, time,
unistd, getopt, fcntl) and the standalone shim sources (errno_map,
env, sysconf, mman, flock, dlfcn, ids, if_query, resolver, sockets).

The test subdirectory is added through a new helper in windows.cmake
guarded on BUILD_TESTING so non-test configurations are unaffected.

Signed-off-by: Nuno Marques <n.marques21@hotmail.com>

platforms/posix/CMakeLists.txt

@@ -107,6 +107,7 @@ target_link_libraries(px4 PRIVATE uORB)
 
 if(WIN32)
 	px4_posix_windows_link_libraries(px4)
+	px4_posix_windows_add_tests()
 endif()
 
 #=============================================================================

platforms/posix/cmake/windows.cmake

@@ -173,3 +173,13 @@ function(px4_posix_windows_link_libraries target_name)
 		target_link_libraries(${target_name} PRIVATE winpthread)
 	endif()
 endfunction()
+
+# Wire up the shim unit tests under platforms/posix/src/px4/windows/tests
+# when CMake testing is configured. The tests are gated to Windows hosts.
+function(px4_posix_windows_add_tests)
+	if(NOT BUILD_TESTING)
+		return()
+	endif()
+	add_subdirectory(${PX4_POSIX_WINDOWS_ROOT}/tests
+		${CMAKE_BINARY_DIR}/platforms/posix/src/px4/windows/tests)
+endfunction()

platforms/posix/src/px4/windows/tests/CMakeLists.txt

@@ -0,0 +1,93 @@
+############################################################################
+#
+#   Copyright (c) 2026 PX4 Development Team. All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+#
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in
+#    the documentation and/or other materials provided with the
+#    distribution.
+# 3. Neither the name PX4 nor the names of its contributors may be
+#    used to endorse or promote products derived from this software
+#    without specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+# FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+# COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+# BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+# OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+# AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
+# ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+# POSSIBILITY OF SUCH DAMAGE.
+#
+############################################################################
+
+#
+# Unit tests for the Windows POSIX shim layer. These targets only build
+# when CMAKE_TESTING is on (BUILD_TESTING is set by include(CTest)).
+# Tests are gated to Windows hosts because the shim headers are
+# Windows-only by design; on non-Windows the .cpp files compile to a
+# trivial sentinel test so the gtest runner still produces output.
+#
+
+if(NOT BUILD_TESTING)
+	return()
+endif()
+
+# Headers-only tests (libgen, dirent, sched, syslog, mman, time, unistd,
+# getopt, fcntl). The translation unit pulls the shim headers via the
+# existing windows_shim include path; no extra link libraries are
+# required beyond gtest itself.
+px4_add_unit_gtest(SRC test_windows_shim_headers.cpp)
+
+# Source-defined shim tests (errno_map, env, sysconf, mman, flock, dlfcn,
+# ids, if_query, resolver, socket loopback). Pulls in the standalone
+# Windows shim sources directly so the tests do not need the full PX4
+# platform/uORB stack.
+set(_px4_windows_shim_root ${CMAKE_CURRENT_SOURCE_DIR}/..)
+
+set(_px4_windows_shim_test_srcs
+	${_px4_windows_shim_root}/posix/sys/errno_map.cpp
+	${_px4_windows_shim_root}/posix/sys/sysconf.cpp
+	${_px4_windows_shim_root}/posix/proc/env.cpp
+	${_px4_windows_shim_root}/posix/proc/ids.cpp
+	${_px4_windows_shim_root}/posix/fs/flock.cpp
+	${_px4_windows_shim_root}/posix/fs/mman.cpp
+	${_px4_windows_shim_root}/posix/lib/dlfcn.cpp
+	${_px4_windows_shim_root}/posix/net/if_query.cpp
+	${_px4_windows_shim_root}/posix/net/resolver.cpp
+)
+
+px4_add_unit_gtest(
+	SRC test_windows_shim_runtime.cpp
+	EXTRA_SRCS ${_px4_windows_shim_test_srcs}
+	INCLUDES
+		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
+		${_px4_windows_shim_root}/include
+	LINKLIBS ws2_32 iphlpapi
+)
+
+# poll() inline implementation - header-only test.
+px4_add_unit_gtest(
+	SRC test_windows_shim_poll.cpp
+	INCLUDES
+		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
+	LINKLIBS ws2_32
+)
+
+# I/O helpers (pipe, fsync, dprintf, mkdir, lstat). Header-only; the
+# POSIX names route to MSVC CRT primitives via inline shim wrappers.
+px4_add_unit_gtest(
+	SRC test_windows_shim_io.cpp
+	INCLUDES
+		${PX4_SOURCE_DIR}/platforms/posix/include/windows_shim
+)