dm: test: Add a very simple of-platadata test

At present we have a pytest that covers of-platadata. Add a very simple
unit test that just checks that a device can be found. This shows the
ability to write these tests in C.

Signed-off-by: Simon Glass <sjg@chromium.org>

test/dm/Makefile

@@ -6,7 +6,9 @@ obj-$(CONFIG_UT_DM) += test-main.o
 
 # Tests for particular subsystems - when enabling driver model for a new
 # subsystem you must add sandbox tests here.
-ifeq ($(CONFIG_SPL_BUILD),)
+ifeq ($(CONFIG_SPL_BUILD),y)
+obj-$(CONFIG_SPL_OF_PLATDATA) += of_platdata.o
+else
 obj-$(CONFIG_UT_DM) += bus.o
 obj-$(CONFIG_UT_DM) += test-driver.o
 obj-$(CONFIG_UT_DM) += test-fdt.o

test/dm/of_platdata.c

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <common.h>
+#include <dm.h>
+#include <dm/test.h>
+#include <test/test.h>
+#include <test/ut.h>
+
+/* Test that we can find a device using of-platdata */
+static int dm_test_of_platdata_base(struct unit_test_state *uts)
+{
+	struct udevice *dev;
+
+	ut_assertok(uclass_first_device_err(UCLASS_SERIAL, &dev));
+	ut_asserteq_str("sandbox_serial", dev->name);
+
+	return 0;
+}
+DM_TEST(dm_test_of_platdata_base, UT_TESTF_SCAN_PDATA);