From: Brendan Higgins <brendanhigg...@google.com>

Introduce basic class mocking, the ability to automatically generate a
Linux C-style class implementation whose behavior is controlled by test
cases, which can also set expectations on when and how mocks are called.

Co-developed-by: Daniel Latypov <dlaty...@google.com>
Signed-off-by: Daniel Latypov <dlaty...@google.com>
Signed-off-by: Brendan Higgins <brendanhigg...@google.com>
---
 include/kunit/mock.h           | 433 +++++++++++++++++++++++++++++++++
 lib/kunit/Makefile             |   5 +-
 lib/kunit/kunit-example-test.c |  98 ++++++++
 lib/kunit/mock-macro-test.c    |  91 +++++++
 lib/kunit/mock-test.c          | 320 ++++++++++++++++++++++++
 5 files changed, 945 insertions(+), 2 deletions(-)
 create mode 100644 lib/kunit/mock-test.c

diff --git a/include/kunit/mock.h b/include/kunit/mock.h
index 13fdeb8730b5..9252a0abd295 100644
--- a/include/kunit/mock.h
+++ b/include/kunit/mock.h
@@ -123,6 +123,439 @@ struct mock_expectation *mock_add_matcher(struct mock 
*mock,
                                          struct mock_param_matcher *matchers[],
                                          int len);
 
+#define MOCK(name) name##_mock
+
+/**
+ * KUNIT_EXPECT_CALL() - Declares a *call expectation* on a mock function.
+ * @expectation_call: a mocked method or function with parameters replaced with
+ *                    matchers.
+ *
+ * Example:
+ *
+ * .. code-block:: c
+ *
+ *     // Class to mock.
+ *     struct example {
+ *             int (*foo)(struct example *, int);
+ *     };
+ *
+ *     // Define the mock.
+ *     DECLARE_STRUCT_CLASS_MOCK_PREREQS(example);
+ *
+ *     DEFINE_STRUCT_CLASS_MOCK(METHOD(foo), CLASS(example),
+ *                              RETURNS(int),
+ *                              PARAMS(struct example *, int));
+ *
+ *     static int example_init(struct MOCK(example) *mock_example)
+ *     {
+ *             struct example *example = mock_get_trgt(mock_example);
+ *
+ *             example->foo = foo;
+ *             return 0;
+ *     }
+ *
+ *     DEFINE_STRUCT_CLASS_MOCK_INIT(example, example_init);
+ *
+ *     static void foo_example_test_success(struct kunit *test)
+ *     {
+ *             struct MOCK(example) *mock_example;
+ *             struct example *example = mock_get_trgt(mock_example);
+ *             struct mock_expectation *handle;
+ *
+ *             mock_example = CONSTRUCT_MOCK(example, test);
+ *
+ *             handle = KUNIT_EXPECT_CALL(foo(mock_get_ctrl(mock_example),
+ *                                            kunit_int_eq(test, 5)));
+ *             handle->action = int_return(test, 2);
+ *
+ *             KUNIT_EXPECT_EQ(test, 2, example_bar(example, 5));
+ *     }
+ *
+ * Return:
+ * A &struct mock_expectation representing the call expectation.
+ * allowing additional conditions and actions to be specified.
+ */
+#define KUNIT_EXPECT_CALL(expectation_call) mock_master_##expectation_call
+
+#define mock_get_ctrl_internal(mock_object) (&(mock_object)->ctrl)
+#define mock_get_ctrl(mock_object) mock_get_ctrl_internal(mock_object)
+
+#define mock_get_trgt_internal(mock_object) (&(mock_object)->trgt)
+#define mock_get_trgt(mock_object) mock_get_trgt_internal(mock_object)
+
+#define mock_get_test(mock_object) (mock_get_ctrl(mock_object)->test)
+
+#define CLASS(struct_name) struct_name
+#define HANDLE_INDEX(index) index
+#define METHOD(method_name) method_name
+#define RETURNS(return_type) return_type
+/* #define PARAMS(...) __VA_ARGS__ included by linux/tracepoint.h */
+
+#define MOCK_INIT_ID(struct_name) struct_name##mock_init
+#define REAL_ID(func_name) __real__##func_name
+#define INVOKE_ID(func_name) __invoke__##func_name
+
+#define DECLARE_MOCK_CLIENT(name, return_type, param_types...) \
+               return_type name(PARAM_LIST_FROM_TYPES(param_types))
+
+#define DECLARE_MOCK_MASTER(name, ctrl_index, param_types...)                 \
+               struct mock_expectation *mock_master_##name(                   \
+                               MATCHER_PARAM_LIST_FROM_TYPES(ctrl_index,      \
+                                                             param_types))
+
+#define DECLARE_MOCK_COMMON(name, handle_index, return_type, param_types...)   
\
+               DECLARE_MOCK_CLIENT(name, return_type, param_types);           \
+               DECLARE_MOCK_MASTER(name, handle_index, param_types)
+
+#define DECLARE_STRUCT_CLASS_MOCK_STRUCT(struct_name)                         \
+               struct MOCK(struct_name) {                                     \
+                       struct mock             ctrl;                          \
+                       struct struct_name      trgt;                          \
+               }
+
+#define DECLARE_STRUCT_CLASS_MOCK_CONVERTER(struct_name)                      \
+               static inline struct mock *from_##struct_name##_to_mock(       \
+                               const struct struct_name *trgt)                \
+               {                                                              \
+                       return mock_get_ctrl(                                  \
+                                       container_of(trgt,                     \
+                                                    struct MOCK(struct_name), \
+                                                    trgt));                   \
+               }
+
+/**
+ * DECLARE_STRUCT_CLASS_MOCK_PREREQS() - Create a mock child class
+ * @struct_name: name of the class/struct to be mocked
+ *
+ * Creates a mock child class of ``struct_name`` named
+ * ``struct MOCK(struct_name)`` along with supporting internally used methods.
+ *
+ * See KUNIT_EXPECT_CALL() for example usages.
+ */
+#define DECLARE_STRUCT_CLASS_MOCK_PREREQS(struct_name)                        \
+               DECLARE_STRUCT_CLASS_MOCK_STRUCT(struct_name);                 \
+               DECLARE_STRUCT_CLASS_MOCK_CONVERTER(struct_name)
+
+#define DECLARE_STRUCT_CLASS_MOCK_HANDLE_INDEX_INTERNAL(name,                 \
+                                                       struct_name,           \
+                                                       handle_index,          \
+                                                       return_type,           \
+                                                       param_types...)        \
+               DECLARE_MOCK_COMMON(name,                                      \
+                                   handle_index,                              \
+                                   return_type,                               \
+                                   param_types)
+
+#define DECLARE_STRUCT_CLASS_MOCK_HANDLE_INDEX(name,                          \
+                                              struct_name,                    \
+                                              handle_index,                   \
+                                              return_type,                    \
+                                              param_types...)                 \
+               DECLARE_STRUCT_CLASS_MOCK_HANDLE_INDEX_INTERNAL(name,          \
+                                                               struct_name,   \
+                                                               handle_index,  \
+                                                               return_type,   \
+                                                               param_types)
+
+/**
+ * DECLARE_STRUCT_CLASS_MOCK()
+ * @name: method name
+ * @struct_name: name of the class/struct
+ * @return_type: return type of the method
+ * @param_types: parameters of the method
+ *
+ * Same as DEFINE_STRUCT_CLASS_MOCK(), but only makes header compatible
+ * declarations.
+ */
+#define DECLARE_STRUCT_CLASS_MOCK(name,                                        
       \
+                                 struct_name,                                 \
+                                 return_type,                                 \
+                                 param_types...)                              \
+               DECLARE_STRUCT_CLASS_MOCK_HANDLE_INDEX(name,                   \
+                                                      struct_name,            \
+                                                      0,                      \
+                                                      return_type,            \
+                                                      param_types)
+
+/**
+ * DECLARE_STRUCT_CLASS_MOCK_VOID_RETURN()
+ * @name: method name
+ * @struct_name: name of the class/struct
+ * @param_types: parameters of the method
+ *
+ * Same as DEFINE_STRUCT_CLASS_MOCK_VOID_RETURN(), but only makes header
+ * compatible declarations.
+ */
+#define DECLARE_STRUCT_CLASS_MOCK_VOID_RETURN(name,                           \
+                                             struct_name,                     \
+                                             param_types...)                  \
+               DECLARE_STRUCT_CLASS_MOCK_HANDLE_INDEX(name,                   \
+                                                      struct_name,            \
+                                                      0,                      \
+                                                      void,                   \
+                                                      param_types)
+
+/**
+ * DECLARE_STRUCT_CLASS_MOCK_INIT()
+ * @struct_name: name of the class/struct
+ *
+ * Same as DEFINE_STRUCT_CLASS_MOCK_INIT(), but only makes header compatible
+ * declarations.
+ */
+#define DECLARE_STRUCT_CLASS_MOCK_INIT(struct_name)                           \
+               struct MOCK(struct_name) *MOCK_INIT_ID(struct_name)(           \
+                               struct kunit *test)
+
+/**
+ * CONSTRUCT_MOCK()
+ * @struct_name: name of the class
+ * @test: associated test
+ *
+ * Constructs and allocates a test managed ``struct MOCK(struct_name)`` given
+ * the name of the class for which the mock is defined and a test object.
+ *
+ * See KUNIT_EXPECT_CALL() for example usage.
+ */
+#define CONSTRUCT_MOCK(struct_name, test) MOCK_INIT_ID(struct_name)(test)
+
+#define DEFINE_MOCK_CLIENT_COMMON(name,                                        
       \
+                                 handle_index,                                \
+                                 MOCK_SOURCE,                                 \
+                                 mock_source_ctx,                             \
+                                 return_type,                                 \
+                                 RETURN,                                      \
+                                 param_types...)                              \
+               return_type name(PARAM_LIST_FROM_TYPES(param_types))           \
+               {                                                              \
+                       struct mock *mock = MOCK_SOURCE(mock_source_ctx,       \
+                                                       handle_index);         \
+                       static const char * const param_type_names[] = {       \
+                               TYPE_NAMES_FROM_TYPES(handle_index,            \
+                                                     param_types)             \
+                       };                                                     \
+                       const void *params[] = {                               \
+                               PTR_TO_ARG_FROM_TYPES(handle_index,            \
+                                                     param_types)             \
+                       };                                                     \
+                       const void *retval;                                    \
+                                                                              \
+                       retval = mock->do_expect(mock,                         \
+                                                #name,                        \
+                                                name,                         \
+                                                param_type_names,             \
+                                                params,                       \
+                                                ARRAY_SIZE(params));          \
+                       KUNIT_ASSERT_NOT_ERR_OR_NULL(mock->test, retval);      \
+                       if (!retval) {                                         \
+                               kunit_info(mock->test,                         \
+                                          "no action installed for 
"#name"\n");\
+                               BUG();                                         \
+                       }                                                      \
+                       RETURN(return_type, retval);                           \
+               }
+
+#define CLASS_MOCK_CLIENT_SOURCE(ctx, handle_index) ctx(arg##handle_index)
+#define DEFINE_MOCK_METHOD_CLIENT_COMMON(name,                                \
+                                        handle_index,                         \
+                                        mock_converter,                       \
+                                        return_type,                          \
+                                        RETURN,                               \
+                                        param_types...)                       \
+               DEFINE_MOCK_CLIENT_COMMON(name,                                \
+                                         handle_index,                        \
+                                         CLASS_MOCK_CLIENT_SOURCE,            \
+                                         mock_converter,                      \
+                                         return_type,                         \
+                                         RETURN,                              \
+                                         param_types)
+
+#define CAST_AND_RETURN(return_type, retval) return *((return_type *) retval)
+#define NO_RETURN(return_type, retval)
+
+#define DEFINE_MOCK_METHOD_CLIENT(name,                                        
       \
+                                 handle_index,                                \
+                                 mock_converter,                              \
+                                 return_type,                                 \
+                                 param_types...)                              \
+               DEFINE_MOCK_METHOD_CLIENT_COMMON(name,                         \
+                                                handle_index,                 \
+                                                mock_converter,               \
+                                                return_type,                  \
+                                                CAST_AND_RETURN,              \
+                                                param_types)
+
+#define DEFINE_MOCK_METHOD_CLIENT_VOID_RETURN(name,                           \
+                                             handle_index,                    \
+                                             mock_converter,                  \
+                                             param_types...)                  \
+               DEFINE_MOCK_METHOD_CLIENT_COMMON(name,                         \
+                                                handle_index,                 \
+                                                mock_converter,               \
+                                                void,                         \
+                                                NO_RETURN,                    \
+                                                param_types)
+
+#define DEFINE_MOCK_MASTER_COMMON_INTERNAL(name,                              \
+                                          ctrl_index,                         \
+                                          MOCK_SOURCE,                        \
+                                          param_types...)                     \
+               struct mock_expectation *mock_master_##name(                   \
+                               MATCHER_PARAM_LIST_FROM_TYPES(ctrl_index,      \
+                                                             param_types))    \
+               { \
+                       struct mock_param_matcher *matchers[] = {              \
+                               ARG_NAMES_FROM_TYPES(ctrl_index, param_types)  \
+                       };                                                     \
+                                                                              \
+                       return mock_add_matcher(MOCK_SOURCE(ctrl_index),       \
+                                               #name,                         \
+                                               (const void *) name,           \
+                                               matchers,                      \
+                                               ARRAY_SIZE(matchers));         \
+               }
+#define DEFINE_MOCK_MASTER_COMMON(name,                                        
       \
+                                 ctrl_index,                                  \
+                                 MOCK_SOURCE,                                 \
+                                 param_types...)                              \
+               DEFINE_MOCK_MASTER_COMMON_INTERNAL(name,                       \
+                                                  ctrl_index,                 \
+                                                  MOCK_SOURCE,                \
+                                                  param_types)
+
+#define CLASS_MOCK_MASTER_SOURCE(ctrl_index) arg##ctrl_index
+#define DEFINE_MOCK_METHOD_MASTER(name, ctrl_index, param_types...)           \
+               DEFINE_MOCK_MASTER_COMMON(name,                                \
+                                         ctrl_index,                          \
+                                         CLASS_MOCK_MASTER_SOURCE,            \
+                                         param_types)
+
+#define DEFINE_MOCK_COMMON(name,                                              \
+                          handle_index,                                       \
+                          mock_converter,                                     \
+                          return_type,                                        \
+                          param_types...)                                     \
+               DEFINE_MOCK_METHOD_CLIENT(name,                                \
+                                         handle_index,                        \
+                                         mock_converter,                      \
+                                         return_type,                         \
+                                         param_types);                        \
+               DEFINE_MOCK_METHOD_MASTER(name, handle_index, param_types)
+
+#define DEFINE_MOCK_COMMON_VOID_RETURN(name,                                  \
+                                      handle_index,                           \
+                                      mock_converter,                         \
+                                      param_types...)                         \
+               DEFINE_MOCK_METHOD_CLIENT_VOID_RETURN(name,                    \
+                                                     handle_index,            \
+                                                     mock_converter,          \
+                                                     param_types);            \
+               DEFINE_MOCK_METHOD_MASTER(name, handle_index, param_types)
+
+#define DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_INTERNAL(name,                  \
+                                                      struct_name,            \
+                                                      handle_index,           \
+                                                      return_type,            \
+                                                      param_types...)         \
+               DEFINE_MOCK_COMMON(name,                                       \
+                                  handle_index,                               \
+                                  from_##struct_name##_to_mock,               \
+                                  return_type, param_types)
+#define DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX(name,                           \
+                                             struct_name,                     \
+                                             handle_index,                    \
+                                             return_type,                     \
+                                             param_types...)                  \
+               DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_INTERNAL(name,           \
+                                                              struct_name,    \
+                                                              handle_index,   \
+                                                              return_type,    \
+                                                              param_types)
+
+#define DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_VOID_RETURN_INTERNAL(           \
+               name,                                                          \
+               struct_name,                                                   \
+               handle_index,                                                  \
+               param_types...)                                                \
+               DEFINE_MOCK_COMMON_VOID_RETURN(name,                           \
+                                              handle_index,                   \
+                                              from_##struct_name##_to_mock,   \
+                                              param_types)
+#define DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_VOID_RETURN(name,                
       \
+                                                         struct_name,         \
+                                                         handle_index,        \
+                                                         param_types...)      \
+               DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_VOID_RETURN_INTERNAL(    \
+                               name,                                          \
+                               struct_name,                                   \
+                               handle_index,                                  \
+                               param_types)
+
+/**
+ * DEFINE_STRUCT_CLASS_MOCK()
+ * @name: name of the method
+ * @struct_name: name of the class of which the method belongs
+ * @return_type: return type of the method to be created. **Must not be void.**
+ * @param_types: parameters to method to be created.
+ *
+ * See KUNIT_EXPECT_CALL() for example usage.
+ */
+#define DEFINE_STRUCT_CLASS_MOCK(name,                                        \
+                                struct_name,                                  \
+                                return_type,                                  \
+                                param_types...)                               \
+               DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX(name,                    \
+                                                     struct_name,             \
+                                                     0,                       \
+                                                     return_type,             \
+                                                     param_types)
+
+/**
+ * DEFINE_STRUCT_CLASS_MOCK_VOID_RETURN()
+ * @name: name of the method
+ * @struct_name: name of the class of which the method belongs
+ * @param_types: parameters to method to be created.
+ *
+ * Same as DEFINE_STRUCT_CLASS_MOCK() except the method has a ``void`` return
+ * type.
+ */
+#define DEFINE_STRUCT_CLASS_MOCK_VOID_RETURN(name, struct_name, 
param_types...)\
+               DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX_VOID_RETURN(name,        \
+                                                                 struct_name, \
+                                                                 0,           \
+                                                                 param_types)
+
+/**
+ * DEFINE_STRUCT_CLASS_MOCK_INIT()
+ * @struct_name: name of the class
+ * @init_func: a function of type ``int (*)(struct kunit *, struct 
MOCK(struct_name) *)``.
+ *             The function is passed a pointer to an allocated, *but not
+ *             initialized*, ``struct MOCK(struct_name)``. The job of this user
+ *             provided function is to perform remaining initialization. 
Usually
+ *             this entails assigning mock methods to the function pointers in
+ *             the parent struct.
+ *
+ * See KUNIT_EXPECT_CALL() for example usage.
+ */
+#define DEFINE_STRUCT_CLASS_MOCK_INIT(struct_name, init_func)                 \
+               struct MOCK(struct_name) *MOCK_INIT_ID(struct_name)(           \
+                               struct kunit *test)                            \
+               {                                                              \
+                       struct MOCK(struct_name) *mock_obj;                    \
+                                                                              \
+                       mock_obj = kunit_kzalloc(test,                         \
+                                               sizeof(*mock_obj),             \
+                                               GFP_KERNEL);                   \
+                       if (!mock_obj)                                         \
+                               return NULL;                                   \
+                                                                              \
+                       mock_init_ctrl(test, mock_get_ctrl(mock_obj));         \
+                                                                              \
+                       if (init_func(test, mock_obj))                         \
+                               return NULL;                                   \
+                                                                              \
+                       return mock_obj;                                       \
+               }
+
 #define CONVERT_TO_ACTUAL_TYPE(type, ptr) (*((type *) ptr))
 
 /**
diff --git a/lib/kunit/Makefile b/lib/kunit/Makefile
index a7a3c5e0a8bf..649e1c1f0d00 100644
--- a/lib/kunit/Makefile
+++ b/lib/kunit/Makefile
@@ -13,11 +13,12 @@ kunit-objs +=                               debugfs.o
 endif
 
 obj-$(CONFIG_KUNIT_TEST) +=            kunit-test.o \
-                                       mock-macro-test.o
+                                       mock-macro-test.o \
+                                       mock-test.o
 
 # string-stream-test compiles built-in only.
 ifeq ($(CONFIG_KUNIT_TEST),y)
 obj-$(CONFIG_KUNIT_TEST) +=            string-stream-test.o
 endif
 
-obj-$(CONFIG_KUNIT_EXAMPLE_TEST) +=    kunit-example-test.o
+obj-$(CONFIG_KUNIT_EXAMPLE_TEST)       += kunit-example-test.o
diff --git a/lib/kunit/kunit-example-test.c b/lib/kunit/kunit-example-test.c
index be1164ecc476..d6fff5a961ce 100644
--- a/lib/kunit/kunit-example-test.c
+++ b/lib/kunit/kunit-example-test.c
@@ -7,6 +7,7 @@
  */
 
 #include <kunit/test.h>
+#include <kunit/mock.h>
 
 /*
  * This is the most fundamental element of KUnit, the test case. A test case
@@ -29,6 +30,92 @@ static void example_simple_test(struct kunit *test)
        KUNIT_EXPECT_EQ(test, 1 + 1, 2);
 }
 
+struct example_ops;
+
+struct example {
+  struct example_ops *ops;
+};
+
+/*
+ * A lot of times, we embed "ops structs", which acts an abstraction over
+ * hardware, a file system implementation, or some other subsystem that you
+ * want to reason about in a generic way.
+ */
+struct example_ops {
+       int (*foo)(struct example *example, int num);
+};
+
+static int example_bar(struct example *example, int num)
+{
+       return example->ops->foo(example, num);
+}
+
+/*
+ * KUnit allows such a class to be "mocked out" with the following:
+ */
+
+/*
+ * This macro creates a mock subclass of the specified class.
+ */
+DECLARE_STRUCT_CLASS_MOCK_PREREQS(example);
+
+/*
+ * This macro creates a mock implementation of the specified method of the
+ * specified class.
+ */
+DEFINE_STRUCT_CLASS_MOCK(METHOD(foo), CLASS(example),
+                        RETURNS(int),
+                        PARAMS(struct example *, int));
+
+/*
+ * This tells KUnit how to initialize the parts of the mock that come from the
+ * parent. In this example, all we have to do is populate the member functions
+ * of the parent class with the mock versions we defined.
+ */
+static int example_init(struct kunit *test, struct MOCK(example) *mock_example)
+{
+       /* This is how you get a pointer to the parent class of a mock. */
+       struct example *example = mock_get_trgt(mock_example);
+
+       /*
+        * Here we create an ops struct containing our mock method instead.
+        */
+       example->ops = kunit_kzalloc(test, sizeof(*example->ops), GFP_KERNEL);
+       example->ops->foo = foo;
+
+       return 0;
+}
+
+/*
+ * This registers our parent init function above, allowing KUnit to create a
+ * constructor for the mock.
+ */
+DEFINE_STRUCT_CLASS_MOCK_INIT(example, example_init);
+
+/*
+ * This is a test case where we use our mock.
+ */
+static void example_mock_test(struct kunit *test)
+{
+       struct MOCK(example) *mock_example = test->priv;
+       struct example *example = mock_get_trgt(mock_example);
+       struct mock_expectation *handle;
+
+       /*
+        * Here we make an expectation that our mock method will be called with
+        * a parameter equal to 5 passed in.
+        */
+       handle = KUNIT_EXPECT_CALL(foo(mock_get_ctrl(mock_example),
+                                      kunit_int_eq(test, 5)));
+       /*
+        * We specify that when our mock is called in this way, we want it to
+        * return 2.
+        */
+       handle->action = kunit_int_return(test, 2);
+
+       KUNIT_EXPECT_EQ(test, 2, example_bar(example, 5));
+}
+
 /*
  * This is run once before each test case, see the comment on
  * example_test_suite for more information.
@@ -37,6 +124,16 @@ static int example_test_init(struct kunit *test)
 {
        kunit_info(test, "initializing\n");
 
+       /*
+        * Here we construct the mock and store it in test's `priv` field; this
+        * field is for KUnit users. You can put whatever you want here, but
+        * most often it is a place that the init function can put stuff to be
+        * used by test cases.
+        */
+       test->priv = CONSTRUCT_MOCK(example, test);
+       if (!test->priv)
+               return -EINVAL;
+
        return 0;
 }
 
@@ -52,6 +149,7 @@ static struct kunit_case example_test_cases[] = {
         * test suite.
         */
        KUNIT_CASE(example_simple_test),
+       KUNIT_CASE(example_mock_test),
        {}
 };
 
diff --git a/lib/kunit/mock-macro-test.c b/lib/kunit/mock-macro-test.c
index 6c3dc2193edb..d196dbee2407 100644
--- a/lib/kunit/mock-macro-test.c
+++ b/lib/kunit/mock-macro-test.c
@@ -8,6 +8,55 @@
 
 #include <kunit/test.h>
 #include <kunit/params.h>
+#include <kunit/mock.h>
+
+struct mock_macro_dummy_struct {
+       int (*one_param)(struct mock_macro_dummy_struct *test_struct);
+       int (*two_param)(struct mock_macro_dummy_struct *test_struct, int num);
+       int (*non_first_slot_param)(
+                       int num,
+                       struct mock_macro_dummy_struct *test_struct);
+       void *(*void_ptr_return)(struct mock_macro_dummy_struct *test_struct);
+};
+
+DECLARE_STRUCT_CLASS_MOCK_PREREQS(mock_macro_dummy_struct);
+
+DEFINE_STRUCT_CLASS_MOCK(METHOD(one_param), CLASS(mock_macro_dummy_struct),
+                        RETURNS(int),
+                        PARAMS(struct mock_macro_dummy_struct *));
+
+DEFINE_STRUCT_CLASS_MOCK(METHOD(two_param), CLASS(mock_macro_dummy_struct),
+                        RETURNS(int),
+                        PARAMS(struct mock_macro_dummy_struct *, int));
+
+DEFINE_STRUCT_CLASS_MOCK_HANDLE_INDEX(METHOD(non_first_slot_param),
+                        CLASS(mock_macro_dummy_struct), HANDLE_INDEX(1),
+                        RETURNS(int),
+                        PARAMS(int, struct mock_macro_dummy_struct *));
+
+DEFINE_STRUCT_CLASS_MOCK(METHOD(void_ptr_return),
+                        CLASS(mock_macro_dummy_struct),
+                        RETURNS(void *),
+                        PARAMS(struct mock_macro_dummy_struct *));
+
+static int mock_macro_dummy_struct_init(
+               struct MOCK(mock_macro_dummy_struct) *mock_test_struct)
+{
+       struct mock_macro_dummy_struct *test_struct =
+                       mock_get_trgt(mock_test_struct);
+
+       test_struct->one_param = one_param;
+       test_struct->two_param = two_param;
+       test_struct->non_first_slot_param = non_first_slot_param;
+       return 0;
+}
+
+DEFINE_STRUCT_CLASS_MOCK_INIT(mock_macro_dummy_struct,
+                             mock_macro_dummy_struct_init);
+
+struct mock_macro_context {
+       struct MOCK(mock_macro_dummy_struct) *mock_test_struct;
+};
 
 #define TO_STR_INTERNAL(...) #__VA_ARGS__
 #define TO_STR(...) TO_STR_INTERNAL(__VA_ARGS__)
@@ -132,6 +181,46 @@ static void mock_macro_arg_names_from_types(struct kunit 
*test)
                                                      type15)));
 }
 
+static void mock_macro_test_generated_method_code_works(struct kunit *test)
+{
+       struct mock_macro_context *ctx = test->priv;
+       struct MOCK(mock_macro_dummy_struct) *mock_test_struct =
+                       ctx->mock_test_struct;
+       struct mock_macro_dummy_struct *test_struct =
+                       mock_get_trgt(mock_test_struct);
+       struct mock_expectation *handle;
+
+       handle = KUNIT_EXPECT_CALL(one_param(mock_get_ctrl(mock_test_struct)));
+       handle->action = kunit_int_return(test, 0);
+       handle = KUNIT_EXPECT_CALL(two_param(mock_get_ctrl(mock_test_struct),
+                                            kunit_int_eq(test, 5)));
+       handle->action = kunit_int_return(test, 1);
+       handle = KUNIT_EXPECT_CALL(non_first_slot_param(
+                       kunit_int_eq(test, 5),
+                       mock_get_ctrl(mock_test_struct)));
+       handle->action = kunit_int_return(test, 1);
+
+       test_struct->one_param(test_struct);
+       test_struct->two_param(test_struct, 5);
+       test_struct->non_first_slot_param(5, test_struct);
+}
+
+static int mock_macro_test_init(struct kunit *test)
+{
+       struct mock_macro_context *ctx;
+
+       ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+       if (!ctx)
+               return -ENOMEM;
+       test->priv = ctx;
+
+       ctx->mock_test_struct = CONSTRUCT_MOCK(mock_macro_dummy_struct, test);
+       if (!ctx->mock_test_struct)
+               return -EINVAL;
+
+       return 0;
+}
+
 static struct kunit_case mock_macro_test_cases[] = {
        KUNIT_CASE(mock_macro_is_equal),
        KUNIT_CASE(mock_macro_if),
@@ -140,11 +229,13 @@ static struct kunit_case mock_macro_test_cases[] = {
        KUNIT_CASE(mock_macro_for_each_param),
        KUNIT_CASE(mock_macro_param_list_from_types_basic),
        KUNIT_CASE(mock_macro_arg_names_from_types),
+       KUNIT_CASE(mock_macro_test_generated_method_code_works),
        {}
 };
 
 static struct kunit_suite mock_macro_test_suite = {
        .name = "mock-macro-test",
+       .init = mock_macro_test_init,
        .test_cases = mock_macro_test_cases,
 };
 kunit_test_suite(mock_macro_test_suite);
diff --git a/lib/kunit/mock-test.c b/lib/kunit/mock-test.c
new file mode 100644
index 000000000000..8a0fa33d087c
--- /dev/null
+++ b/lib/kunit/mock-test.c
@@ -0,0 +1,320 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit test for mock.h.
+ *
+ * Copyright (C) 2020, Google LLC.
+ * Author: Brendan Higgins <brendanhigg...@google.com>
+ */
+
+#include <kunit/test.h>
+#include <kunit/mock.h>
+
+// A simple class for unit-testing/example purposes.
+struct adder {
+       int (*add)(struct adder *adder, int x, int y);
+};
+
+static int real_add(struct adder *adder, int x, int y)
+{
+       return x + y;
+}
+
+static void adder_real_init(struct adder *adder)
+{
+         adder->add = real_add;
+}
+
+DECLARE_STRUCT_CLASS_MOCK_PREREQS(adder);
+DEFINE_STRUCT_CLASS_MOCK(METHOD(mock_add), CLASS(adder), RETURNS(int),
+                                    PARAMS(struct adder*, int, int));
+DECLARE_STRUCT_CLASS_MOCK_INIT(adder);
+
+// This would normally live in the .c file.
+static int adder_mock_init(struct MOCK(adder) *mock_adder)
+{
+       struct adder *real = mock_get_trgt(mock_adder);
+
+       adder_real_init(real);
+
+       real->add = mock_add;
+       mock_set_default_action(mock_get_ctrl(mock_adder),
+                               "mock_add",
+                               mock_add,
+                               kunit_int_return(mock_get_test(mock_adder), 0));
+       return 0;
+}
+DEFINE_STRUCT_CLASS_MOCK_INIT(adder, adder_mock_init);
+
+
+/*
+ * Note: we create a new `failing_test` so we can validate that failed mock
+ * expectations mark tests as failed.
+ * Marking the real `test` as failed is obviously problematic.
+ *
+ * See mock_test_failed_expect_call_fails_test for an example.
+ */
+struct mock_test_context {
+       struct kunit *failing_test;
+       struct mock  *mock;
+};
+
+static void mock_test_do_expect_basic(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+       struct mock *mock = ctx->mock;
+       int param0 = 5, param1 = -4;
+       static const char * const two_param_types[] = {"int", "int"};
+       const void *two_params[] = {&param0, &param1};
+       struct mock_param_matcher *matchers_any_two[] = {
+               kunit_any(test), kunit_any(test)
+       };
+       struct mock_expectation *expectation;
+       const void *ret;
+
+       expectation = mock_add_matcher(mock,
+                                      "",
+                                      NULL,
+                                      matchers_any_two,
+                                      ARRAY_SIZE(matchers_any_two));
+       expectation->action = kunit_int_return(test, 5);
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+
+       ret = mock->do_expect(mock,
+                             "",
+                             NULL,
+                             two_param_types,
+                             two_params,
+                             ARRAY_SIZE(two_params));
+       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
+       KUNIT_EXPECT_EQ(test, 5, *((int *) ret));
+       KUNIT_EXPECT_EQ(test, 1, expectation->times_called);
+}
+
+static void mock_test_ptr_eq(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+       struct kunit *failing_test = ctx->failing_test;
+       struct mock *mock = ctx->mock;
+       void *param0 = ctx, *param1 = failing_test;
+       static const char * const two_param_types[] = {"void *", "void *"};
+       const void *two_params[] = {&param0, &param1};
+       struct mock_param_matcher *matchers_two_ptrs[] = {
+               kunit_ptr_eq(test, param0), kunit_ptr_eq(test, param1)
+       };
+       struct mock_expectation *expectation;
+       const void *ret;
+
+       expectation = mock_add_matcher(mock,
+                                      "",
+                                      NULL,
+                                      matchers_two_ptrs,
+                                      ARRAY_SIZE(matchers_two_ptrs));
+       expectation->action = kunit_int_return(test, 0);
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+
+       ret = mock->do_expect(mock,
+                             "",
+                             NULL,
+                             two_param_types,
+                             two_params,
+                             ARRAY_SIZE(two_params));
+       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
+       KUNIT_EXPECT_EQ(test, 1, expectation->times_called);
+}
+
+static void mock_test_ptr_eq_not_equal(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+       struct kunit *failing_test = ctx->failing_test;
+       struct mock *mock = ctx->mock;
+
+       /* Pick some two pointers, but pass in different values. */
+       void *param0 = test, *param1 = failing_test;
+       static const char * const two_param_types[] = {"void *", "void *"};
+       const void *two_params[] = {&param0, &param1};
+       struct mock_param_matcher *matchers_two_ptrs[] = {
+               kunit_ptr_eq(failing_test, param0),
+               kunit_ptr_eq(failing_test, param1 - 1)
+       };
+       struct mock_expectation *expectation;
+       const void *ret;
+
+       expectation = mock_add_matcher(mock,
+                                      "",
+                                      NULL,
+                                      matchers_two_ptrs,
+                                      ARRAY_SIZE(matchers_two_ptrs));
+       expectation->action = kunit_int_return(failing_test, 0);
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+
+       ret = mock->do_expect(mock,
+                             "",
+                             NULL,
+                             two_param_types,
+                             two_params,
+                             ARRAY_SIZE(two_params));
+       KUNIT_EXPECT_FALSE(test, ret);
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+
+       KUNIT_EXPECT_FALSE(test, failing_test->success);
+}
+
+/*
+ * In order for us to be able to rely on KUNIT_EXPECT_CALL to validate other
+ * behavior, we need to test that unsatisfied KUNIT_EXPECT_CALL causes a test
+ * failure.
+ *
+ * In order to understand what this test is testing we must first understand 
how
+ * KUNIT_EXPECT_CALL() works conceptually. In theory, a test specifies that it
+ * expects some function to be called some number of times (can be zero), with
+ * some particular arguments. Hence, KUNIT_EXPECT_CALL() must do two things:
+ *
+ * 1) Determine whether a function call matches the expectation.
+ *
+ * 2) Fail if there are too many or too few matches.
+ */
+static void mock_test_failed_expect_call_fails_test(struct kunit *test)
+{
+       /*
+       * We do not want to fail the real `test` object used to run this test.
+       * So we use a separate `failing_test` for KUNIT_EXPECT_CALL().
+       */
+       struct mock_test_context *ctx = test->priv;
+       struct kunit *failing_test = ctx->failing_test;
+       struct mock *mock = ctx->mock;
+
+       /*
+        * Put an expectation on mock, which we won't satisify.
+        *
+        * NOTE: it does not actually matter what function we expect here.
+        * `mock` does not represent an actual mock on anything; we just need to
+        * create some expectation, that we won't satisfy.
+        */
+       KUNIT_EXPECT_CALL(mock_add(mock,
+                              kunit_any(failing_test),
+                              kunit_any(failing_test)));
+
+       /*
+        * Validate the unsatisfied expectation that we just created. This
+        * should cause `failing_test` to fail.
+        */
+       mock_validate_expectations(mock);
+
+       /* Verify that `failing_test` has actually failed. */
+       KUNIT_EXPECT_FALSE(test, failing_test->success);
+}
+
+static void mock_test_do_expect_default_return(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+       struct mock *mock = ctx->mock;
+       int param0 = 5, param1 = -5;
+       static const char * const two_param_types[] = {"int", "int"};
+       const void *two_params[] = {&param0, &param1};
+       struct mock_param_matcher *matchers[] = {
+               kunit_int_eq(test, 5),
+               kunit_int_eq(test, -4)
+       };
+       struct mock_expectation *expectation;
+       const void *ret;
+
+       expectation = mock_add_matcher(mock,
+                                      "add",
+                                      mock_add,
+                                      matchers,
+                                      ARRAY_SIZE(matchers));
+       expectation->action = kunit_int_return(test, 5);
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+
+       KUNIT_EXPECT_FALSE(test,
+                          mock_set_default_action(mock,
+                                                  "add",
+                                                  mock_add,
+                                                  kunit_int_return(test, -4)));
+
+       ret = mock->do_expect(mock,
+                             "add",
+                             mock_add,
+                             two_param_types,
+                             two_params,
+                             ARRAY_SIZE(two_params));
+       KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
+       KUNIT_EXPECT_EQ(test, -4, *((int *) ret));
+       KUNIT_EXPECT_EQ(test, 0, expectation->times_called);
+}
+
+static void mock_test_mock_validate_expectations(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+       struct kunit *failing_test = ctx->failing_test;
+       struct mock *mock = ctx->mock;
+
+       struct mock_param_matcher *matchers[] = {
+               kunit_int_eq(failing_test, 5),
+               kunit_int_eq(failing_test, -4)
+       };
+       struct mock_expectation *expectation;
+
+
+       expectation = mock_add_matcher(mock,
+                                      "add",
+                                      mock_add,
+                                      matchers,
+                                      ARRAY_SIZE(matchers));
+       expectation->times_called = 0;
+       expectation->min_calls_expected = 1;
+       expectation->max_calls_expected = 1;
+
+       mock_validate_expectations(mock);
+
+       KUNIT_EXPECT_FALSE(test, failing_test->success);
+}
+
+static int mock_test_init(struct kunit *test)
+{
+       struct mock_test_context *ctx;
+
+       ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
+       if (!ctx)
+               return -ENOMEM;
+       test->priv = ctx;
+
+       ctx->failing_test = kunit_kzalloc(test, sizeof(*ctx->failing_test),
+                                         GFP_KERNEL);
+       if (!ctx->failing_test)
+               return -EINVAL;
+       kunit_init_test(ctx->failing_test, NULL, NULL);
+
+       ctx->mock = kunit_kzalloc(test, sizeof(*ctx->mock), GFP_KERNEL);
+       if (!ctx->mock)
+               return -ENOMEM;
+       mock_init_ctrl(ctx->failing_test, ctx->mock);
+
+       return 0;
+}
+
+static void mock_test_exit(struct kunit *test)
+{
+       struct mock_test_context *ctx = test->priv;
+
+       kunit_cleanup(ctx->failing_test);
+}
+
+static struct kunit_case mock_test_cases[] = {
+       KUNIT_CASE(mock_test_do_expect_basic),
+       KUNIT_CASE(mock_test_ptr_eq),
+       KUNIT_CASE(mock_test_ptr_eq_not_equal),
+       KUNIT_CASE(mock_test_failed_expect_call_fails_test),
+       KUNIT_CASE(mock_test_do_expect_default_return),
+       KUNIT_CASE(mock_test_mock_validate_expectations),
+       {}
+};
+
+static struct kunit_suite mock_test_suite = {
+       .name = "mock-test",
+       .init = mock_test_init,
+       .exit = mock_test_exit,
+       .test_cases = mock_test_cases,
+};
+
+kunit_test_suite(mock_test_suite);
-- 
2.28.0.1011.ga647a8990f-goog

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