leds: Provide skeleton KUnit testing for the LEDs framework

Apply a very basic implementation of KUnit LED testing.

More tests / use-cases will be added steadily over time.

CMD:
  tools/testing/kunit/kunit.py run --kunitconfig drivers/leds

OUTPUT:
  [15:34:19] Configuring KUnit Kernel ...
  [15:34:19] Building KUnit Kernel ...
  Populating config with:
  $ make ARCH=um O=.kunit olddefconfig
  Building with:
  $ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=20
  [15:34:22] Starting KUnit Kernel (1/1)...
  [15:34:22] ============================================================
  Running tests with:
  $ .kunit/linux kunit.enable=1 mem=1G console=tty kunit_shutdown=halt
  [15:34:23] ===================== led (1 subtest) ======================
  [15:34:23] [PASSED] led_test_class_register
  [15:34:23] ======================= [PASSED] led =======================
  [15:34:23] ============================================================
  [15:34:23] Testing complete. Ran 1 tests: passed: 1
  [15:34:23] Elapsed time: 4.268s total, 0.001s configuring, 3.048s building, 1.214s running

Link: https://lore.kernel.org/r/20250424144544.1438584-1-lee@kernel.org
Signed-off-by: Lee Jones <lee@kernel.org>

drivers/leds/.kunitconfig

@@ -0,0 +1,4 @@
+CONFIG_KUNIT=y
+CONFIG_NEW_LEDS=y
+CONFIG_LEDS_CLASS=y
+CONFIG_LEDS_KUNIT_TEST=y

drivers/leds/Kconfig

@@ -55,6 +55,13 @@ config LEDS_BRIGHTNESS_HW_CHANGED
 
 	  See Documentation/ABI/testing/sysfs-class-led for details.
 
+config LEDS_KUNIT_TEST
+	tristate "KUnit tests for LEDs"
+	depends on KUNIT && LEDS_CLASS
+	default KUNIT_ALL_TESTS
+	help
+	  Say Y here to enable KUnit testing for the LEDs framework.
+
 comment "LED drivers"
 
 config LEDS_88PM860X

drivers/leds/Makefile

@@ -6,6 +6,7 @@ obj-$(CONFIG_LEDS_CLASS)		+= led-class.o
 obj-$(CONFIG_LEDS_CLASS_FLASH)		+= led-class-flash.o
 obj-$(CONFIG_LEDS_CLASS_MULTICOLOR)	+= led-class-multicolor.o
 obj-$(CONFIG_LEDS_TRIGGERS)		+= led-triggers.o
+obj-$(CONFIG_LEDS_KUNIT_TEST)		+= led-test.o
 
 # LED Platform Drivers (keep this sorted, M-| sort)
 obj-$(CONFIG_LEDS_88PM860X)		+= leds-88pm860x.o

drivers/leds/led-test.c

@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ *
+ * Author: Lee Jones <lee@kernel.org>
+ */
+
+#include <kunit/device.h>
+#include <kunit/test.h>
+#include <linux/device.h>
+#include <linux/leds.h>
+
+struct led_test_ddata {
+	struct led_classdev cdev;
+	struct device *dev;
+};
+
+static void led_test_class_register(struct kunit *test)
+{
+	struct led_test_ddata *ddata = test->priv;
+	struct led_classdev *cdev = &ddata->cdev;
+	struct device *dev = ddata->dev;
+	int ret;
+
+	cdev->name = "led-test";
+
+	ret = devm_led_classdev_register(dev, cdev);
+	KUNIT_ASSERT_EQ(test, ret, 0);
+	if (ret)
+		return;
+}
+
+static struct kunit_case led_test_cases[] = {
+	KUNIT_CASE(led_test_class_register),
+	{ }
+};
+
+static int led_test_init(struct kunit *test)
+{
+	struct led_test_ddata *ddata;
+	struct device *dev;
+
+	ddata = kunit_kzalloc(test, sizeof(*ddata), GFP_KERNEL);
+	if (!ddata)
+		return -ENOMEM;
+
+	test->priv = ddata;
+
+	dev = kunit_device_register(test, "led_test");
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+
+	ddata->dev = get_device(dev);
+
+	return 0;
+}
+
+static void led_test_exit(struct kunit *test)
+{
+	struct led_test_ddata *ddata = test->priv;
+
+	if (ddata && ddata->dev)
+		put_device(ddata->dev);
+}
+
+static struct kunit_suite led_test_suite = {
+	.name = "led",
+	.init = led_test_init,
+	.exit = led_test_exit,
+	.test_cases = led_test_cases,
+};
+kunit_test_suite(led_test_suite);
+
+MODULE_AUTHOR("Lee Jones <lee@kernel.org>");
+MODULE_DESCRIPTION("KUnit tests for the LED framework");
+MODULE_LICENSE("GPL");