diff --git a/tests/lib/cpp/cxx/prj.conf b/tests/lib/cpp/cxx/prj.conf
index 15ae9ce1ebd4909..158eb89a201e4c0 100644
--- a/tests/lib/cpp/cxx/prj.conf
+++ b/tests/lib/cpp/cxx/prj.conf
@@ -5,8 +5,21 @@ CONFIG_ZTEST_STACK_SIZE=2048
 CONFIG_COMMON_LIBC_MALLOC_ARENA_SIZE=128
 CONFIG_CRC=y
 
+# Enable optional features that are off by default to cover as much as
+# possible of the same .h files. Ideally, kconfiglib.py would support
+# "randconfig" because turning on some options can also reduce test
+# coverage in some areas. But: 1. combinatorial explosion, 2. it does
+# not.
+
 # RTIO
 CONFIG_RTIO=y
 CONFIG_RTIO_SUBMIT_SEM=y
 CONFIG_RTIO_CONSUME_SEM=y
 CONFIG_RTIO_SYS_MEM_BLOCKS=y
+
+# Enable more features and C++ coverage in device.h, pm/device.h, pm.h...
+CONFIG_PM=y
+CONFIG_PM_DEVICE=y
+CONFIG_PM_DEVICE_RUNTIME=y
+# Deprecated but on by default! Silence the warning:
+CONFIG_PM_DEVICE_RUNTIME_EXCLUSIVE=n
diff --git a/tests/lib/cpp/cxx/src/main.cpp b/tests/lib/cpp/cxx/src/main.cpp
index a8a49a3a2540909..8b149290bab6573 100644
--- a/tests/lib/cpp/cxx/src/main.cpp
+++ b/tests/lib/cpp/cxx/src/main.cpp
@@ -15,6 +15,7 @@
 
 #include <zephyr/init.h>
 #include <zephyr/device.h>
+#include <zephyr/pm/device.h>
 #include <zephyr/kernel.h>
 #include <zephyr/net/buf.h>
 #include <zephyr/sys/crc.h>
@@ -147,3 +148,7 @@ ZTEST_SUITE(cxx_tests, NULL, NULL, NULL, NULL, NULL);
 DEVICE_DT_DEFINE(DT_NODELABEL(test_dev0_boot), NULL, NULL, NULL, NULL, POST_KERNEL, 33, NULL);
 
 DEVICE_DT_DEFINE(DT_NODELABEL(test_dev1_dfr), NULL, NULL, NULL, NULL, POST_KERNEL, 33, NULL);
+
+static int fake_pm_action(const struct device *dev,
+		enum pm_device_action pm_action) { return -1; }
+PM_DEVICE_DT_DEFINE(DT_NODELABEL(test_dev0_boot), fake_pm_action);