kunit: Add example parameterized test with direct dynamic parameter array setup

Introduce example_params_test_with_init_dynamic_arr(). This new
KUnit test demonstrates directly assigning a dynamic parameter
array, using the kunit_register_params_array() macro, to a
parameterized test context.

It highlights the use of param_init() and param_exit() for
initialization and exit of a parameterized test, and their
registration to the test case with KUNIT_CASE_PARAM_WITH_INIT().

Link: https://lore.kernel.org/r/20250826091341.1427123-7-davidgow@google.com
Reviewed-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Marie Zhussupova <marievic@google.com>
Signed-off-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

lib/kunit/kunit-example-test.c

@@ -388,6 +388,107 @@ static void example_params_test_with_init(struct kunit *test)
 	kunit_put_resource(res);
 }
 
+/*
+ * Helper function to create a parameter array of Fibonacci numbers. This example
+ * highlights a parameter generation scenario that is:
+ * 1. Not feasible to fully pre-generate at compile time.
+ * 2. Challenging to implement with a standard generate_params() function,
+ * as it only provides the previous parameter, while Fibonacci requires
+ * access to two preceding values for calculation.
+ */
+static void *make_fibonacci_params(struct kunit *test, size_t seq_size)
+{
+	int *seq;
+
+	if (seq_size <= 0)
+		return NULL;
+	/*
+	 * Using kunit_kmalloc_array here ties the lifetime of the array to
+	 * the parameterized test i.e. it will get automatically cleaned up
+	 * by KUnit after the parameterized test finishes.
+	 */
+	seq = kunit_kmalloc_array(test, seq_size, sizeof(int), GFP_KERNEL);
+
+	if (!seq)
+		return NULL;
+	if (seq_size >= 1)
+		seq[0] = 0;
+	if (seq_size >= 2)
+		seq[1] = 1;
+	for (int i = 2; i < seq_size; i++)
+		seq[i] = seq[i - 1] + seq[i - 2];
+	return seq;
+}
+
+/*
+ * This is an example of a function that provides a description for each of the
+ * parameters.
+ */
+static void example_param_dynamic_arr_get_desc(struct kunit *test, const void *p, char *desc)
+{
+	const int *fib_num = p;
+
+	snprintf(desc, KUNIT_PARAM_DESC_SIZE, "fibonacci param: %d", *fib_num);
+}
+
+/*
+ * Example of a parameterized test param_init() function that registers a dynamic
+ * array of parameters.
+ */
+static int example_param_init_dynamic_arr(struct kunit *test)
+{
+	size_t seq_size;
+	int *fibonacci_params;
+
+	kunit_info(test, "initializing parameterized test\n");
+
+	seq_size = 6;
+	fibonacci_params = make_fibonacci_params(test, seq_size);
+
+	if (!fibonacci_params)
+		return -ENOMEM;
+
+	/*
+	 * Passes the dynamic parameter array information to the parameterized test
+	 * context struct kunit. The array and its metadata will be stored in
+	 * test->parent->params_array. The array itself will be located in
+	 * params_data.params.
+	 *
+	 * Note that you will need to pass kunit_array_gen_params() as the
+	 * generator function to KUNIT_CASE_PARAM_WITH_INIT() when registering
+	 * a parameter array this route.
+	 */
+	kunit_register_params_array(test, fibonacci_params, seq_size,
+				    example_param_dynamic_arr_get_desc);
+	return 0;
+}
+
+/*
+ * Example of a parameterized test param_exit() function that outputs a log
+ * at the end of the parameterized test. It could also be used for any other
+ * teardown logic.
+ */
+static void example_param_exit_dynamic_arr(struct kunit *test)
+{
+	kunit_info(test, "exiting parameterized test\n");
+}
+
+/*
+ * Example of test that uses the registered dynamic array to perform assertions
+ * and expectations.
+ */
+static void example_params_test_with_init_dynamic_arr(struct kunit *test)
+{
+	const int *param = test->param_value;
+	int param_val;
+
+	/* By design, param pointer will not be NULL. */
+	KUNIT_ASSERT_NOT_NULL(test, param);
+
+	param_val = *param;
+	KUNIT_EXPECT_EQ(test, param_val - param_val, 0);
+}
+
 /*
  * Here we make a list of all the test cases we want to add to the test suite
  * below.
@@ -409,6 +510,9 @@ static struct kunit_case example_test_cases[] = {
 	KUNIT_CASE_PARAM(example_params_test, example_gen_params),
 	KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, kunit_array_gen_params,
 				   example_param_init, NULL),
+	KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init_dynamic_arr,
+				   kunit_array_gen_params, example_param_init_dynamic_arr,
+				   example_param_exit_dynamic_arr),
 	KUNIT_CASE_SLOW(example_slow_test),
 	{}
 };