[PATCH 7/9] kunit: Add example parameterized test with shared resources and direct static parameter array setup

[Marie Zhussupova <marievic@google.com>]

Add `example_params_test_with_init` to illustrate how to manage
shared resources across parameterized KUnit tests. This example
showcases the use of the new `param_init` function and its registration
to a test using the `KUNIT_CASE_PARAM_WITH_INIT` macro.

Additionally, the test demonstrates:
- How to directly assign a static parameter array to a test via
  `kunit_register_params_array`.
- Leveraging the Resource API for test resource management.

Signed-off-by: Marie Zhussupova <marievic@google.com>
---
 lib/kunit/kunit-example-test.c | 112 +++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)

diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c
index 3056d6bc705d..5bf559e243f6 100644
--- a/lib/kunit/kunit-example-test.c
+++ b/lib/kunit/kunit-example-test.c
@@ -277,6 +277,116 @@ static void example_slow_test(struct kunit *test)
 	KUNIT_EXPECT_EQ(test, 1 + 1, 2);
 }
 
+/*
+ * This custom function allocates memory for the kunit_resource data field.
+ * The function is passed to kunit_alloc_resource() and executed once
+ * by the internal helper __kunit_add_resource().
+ */
+static int example_resource_init(struct kunit_resource *res, void *context)
+{
+	int *info = kmalloc(sizeof(*info), GFP_KERNEL);
+
+	if (!info)
+		return -ENOMEM;
+	*info = *(int *)context;
+	res->data = info;
+	return 0;
+}
+
+/*
+ * This function deallocates memory for the 'kunit_resource' data field.
+ * The function is passed to kunit_alloc_resource() and automatically
+ * executes within kunit_release_resource() when the resource's reference
+ * count, via kunit_put_resource(), drops to zero. KUnit uses reference
+ * counting to ensure that resources are not freed prematurely.
+ */
+static void example_resource_free(struct kunit_resource *res)
+{
+	kfree(res->data);
+}
+
+/*
+ * This match function is invoked by kunit_find_resource() to locate
+ * a test resource based on defined criteria. The current example
+ * uniquely identifies the resource by its free function; however,
+ * alternative custom criteria can be implemented. Refer to
+ * lib/kunit/platform.c and lib/kunit/static_stub.c for further examples.
+ */
+static bool example_resource_alloc_match(struct kunit *test,
+					 struct kunit_resource *res,
+					 void *match_data)
+{
+	return res->data && res->free == example_resource_free;
+}
+
+/*
+ * This is an example of a function that provides a description for each of the
+ * parameters.
+ */
+static void example_param_array_get_desc(const void *p, char *desc)
+{
+	const struct example_param *param = p;
+
+	snprintf(desc, KUNIT_PARAM_DESC_SIZE,
+		 "example check if %d is less than or equal to 3", param->value);
+}
+
+/*
+ * Initializes the parent kunit struct for parameterized KUnit tests.
+ * This function enables sharing resources across all parameterized
+ * tests by adding them to the `parent` kunit test struct. It also supports
+ * registering either static or dynamic arrays of test parameters.
+ */
+static int example_param_init(struct kunit *test)
+{
+	int ctx = 3; /* Data to be stored. */
+	int arr_size = ARRAY_SIZE(example_params_array);
+
+	/*
+	 * This allocates a struct kunit_resource, sets its data field to
+	 * ctx, and adds it to the kunit struct's resources list. Note that
+	 * this is test managed so we don't need to have a custom exit function
+	 * to free it.
+	 */
+	void *data = kunit_alloc_resource(test, example_resource_init, example_resource_free,
+					  GFP_KERNEL, &ctx);
+
+	if (!data)
+		return -ENOMEM;
+	/* Pass the static param array information to the parent struct kunit. */
+	kunit_register_params_array(test, example_params_array, arr_size,
+				    example_param_array_get_desc);
+	return 0;
+}
+
+/*
+ * This is an example of a parameterized test that uses shared resources
+ * available from the struct kunit parent field of the kunit struct.
+ */
+static void example_params_test_with_init(struct kunit *test)
+{
+	int threshold;
+	struct kunit_resource *res;
+	const struct example_param *param = test->param_value;
+
+	/* By design, param pointer will not be NULL. */
+	KUNIT_ASSERT_NOT_NULL(test, param);
+
+	/* Here we access the parent pointer of the test to find the shared resource. */
+	res = kunit_find_resource(test->parent, example_resource_alloc_match, NULL);
+
+	KUNIT_ASSERT_NOT_NULL(test, res);
+
+	/* Since the data field in kunit_resource is a void pointer we need to typecast it. */
+	threshold = *((int *)res->data);
+
+	/* Assert that the parameter is less than or equal to a certain threshold. */
+	KUNIT_ASSERT_LE(test, param->value, threshold);
+
+	/* This decreases the reference count after calling kunit_find_resource(). */
+	kunit_put_resource(res);
+}
+
 /*
  * Here we make a list of all the test cases we want to add to the test suite
  * below.
@@ -296,6 +406,8 @@ static struct kunit_case example_test_cases[] = {
 	KUNIT_CASE(example_static_stub_using_fn_ptr_test),
 	KUNIT_CASE(example_priv_test),
 	KUNIT_CASE_PARAM(example_params_test, example_gen_params),
+	KUNIT_CASE_PARAM_WITH_INIT(example_params_test_with_init, NULL,
+				   example_param_init, NULL),
 	KUNIT_CASE_SLOW(example_slow_test),
 	{}
 };
-- 
2.50.1.552.g942d659e1b-goog