1 .. SPDX-License-Identifier: GPL-2.0 1 .. SPDX-License-Identifier: GPL-2.0
2 2
>> 3 ===========
>> 4 Using KUnit
>> 5 ===========
>> 6
>> 7 The purpose of this document is to describe what KUnit is, how it works, how it
>> 8 is intended to be used, and all the concepts and terminology that are needed to
>> 9 understand it. This guide assumes a working knowledge of the Linux kernel and
>> 10 some basic knowledge of testing.
>> 11
>> 12 For a high level introduction to KUnit, including setting up KUnit for your
>> 13 project, see :doc:`start`.
>> 14
>> 15 Organization of this document
>> 16 =============================
>> 17
>> 18 This document is organized into two main sections: Testing and Isolating
>> 19 Behavior. The first covers what unit tests are and how to use KUnit to write
>> 20 them. The second covers how to use KUnit to isolate code and make it possible
>> 21 to unit test code that was otherwise un-unit-testable.
>> 22
>> 23 Testing
>> 24 =======
>> 25
>> 26 What is KUnit?
>> 27 --------------
>> 28
>> 29 "K" is short for "kernel" so "KUnit" is the "(Linux) Kernel Unit Testing
>> 30 Framework." KUnit is intended first and foremost for writing unit tests; it is
>> 31 general enough that it can be used to write integration tests; however, this is
>> 32 a secondary goal. KUnit has no ambition of being the only testing framework for
>> 33 the kernel; for example, it does not intend to be an end-to-end testing
>> 34 framework.
>> 35
>> 36 What is Unit Testing?
>> 37 ---------------------
>> 38
>> 39 A `unit test <https://martinfowler.com/bliki/UnitTest.html>`_ is a test that
>> 40 tests code at the smallest possible scope, a *unit* of code. In the C
>> 41 programming language that's a function.
>> 42
>> 43 Unit tests should be written for all the publicly exposed functions in a
>> 44 compilation unit; so that is all the functions that are exported in either a
>> 45 *class* (defined below) or all functions which are **not** static.
>> 46
3 Writing Tests 47 Writing Tests
4 ============= !! 48 -------------
5 49
6 Test Cases 50 Test Cases
7 ---------- !! 51 ~~~~~~~~~~
8 52
9 The fundamental unit in KUnit is the test case 53 The fundamental unit in KUnit is the test case. A test case is a function with
10 the signature ``void (*)(struct kunit *test)`` !! 54 the signature ``void (*)(struct kunit *test)``. It calls a function to be tested
11 and then sets *expectations* for what should h 55 and then sets *expectations* for what should happen. For example:
12 56
13 .. code-block:: c 57 .. code-block:: c
14 58
15 void example_test_success(struct kunit 59 void example_test_success(struct kunit *test)
16 { 60 {
17 } 61 }
18 62
19 void example_test_failure(struct kunit 63 void example_test_failure(struct kunit *test)
20 { 64 {
21 KUNIT_FAIL(test, "This test ne 65 KUNIT_FAIL(test, "This test never passes.");
22 } 66 }
23 67
24 In the above example, ``example_test_success`` !! 68 In the above example ``example_test_success`` always passes because it does
25 nothing; no expectations are set, and therefor !! 69 nothing; no expectations are set, so all expectations pass. On the other hand
26 other hand ``example_test_failure`` always fai !! 70 ``example_test_failure`` always fails because it calls ``KUNIT_FAIL``, which is
27 which is a special expectation that logs a mes !! 71 a special expectation that logs a message and causes the test case to fail.
28 fail. <<
29 72
30 Expectations 73 Expectations
31 ~~~~~~~~~~~~ 74 ~~~~~~~~~~~~
32 An *expectation* specifies that we expect a pi !! 75 An *expectation* is a way to specify that you expect a piece of code to do
33 test. An expectation is called like a function !! 76 something in a test. An expectation is called like a function. A test is made
34 expectations about the behavior of a piece of !! 77 by setting expectations about the behavior of a piece of code under test; when
35 expectations fail, the test case fails and inf !! 78 one or more of the expectations fail, the test case fails and information about
36 logged. For example: !! 79 the failure is logged. For example:
37 80
38 .. code-block:: c 81 .. code-block:: c
39 82
40 void add_test_basic(struct kunit *test 83 void add_test_basic(struct kunit *test)
41 { 84 {
42 KUNIT_EXPECT_EQ(test, 1, add(1 85 KUNIT_EXPECT_EQ(test, 1, add(1, 0));
43 KUNIT_EXPECT_EQ(test, 2, add(1 86 KUNIT_EXPECT_EQ(test, 2, add(1, 1));
44 } 87 }
45 88
46 In the above example, ``add_test_basic`` makes !! 89 In the above example ``add_test_basic`` makes a number of assertions about the
47 behavior of a function called ``add``. The fir !! 90 behavior of a function called ``add``; the first parameter is always of type
48 ``struct kunit *``, which contains information !! 91 ``struct kunit *``, which contains information about the current test context;
49 The second parameter, in this case, is what th !! 92 the second parameter, in this case, is what the value is expected to be; the
50 last value is what the value actually is. If ` 93 last value is what the value actually is. If ``add`` passes all of these
51 expectations, the test case, ``add_test_basic` 94 expectations, the test case, ``add_test_basic`` will pass; if any one of these
52 expectations fails, the test case will fail. 95 expectations fails, the test case will fail.
53 96
54 A test case *fails* when any expectation is vi !! 97 It is important to understand that a test case *fails* when any expectation is
55 continue to run, and try other expectations un !! 98 violated; however, the test will continue running, potentially trying other
56 otherwise terminated. This is as opposed to *a !! 99 expectations until the test case ends or is otherwise terminated. This is as
57 later. !! 100 opposed to *assertions* which are discussed later.
58 101
59 To learn about more KUnit expectations, see Do !! 102 To learn about more expectations supported by KUnit, see :doc:`api/test`.
60 103
61 .. note:: 104 .. note::
62 A single test case should be short, easy to !! 105 A single test case should be pretty short, pretty easy to understand,
63 single behavior. !! 106 focused on a single behavior.
64 107
65 For example, if we want to rigorously test the !! 108 For example, if we wanted to properly test the add function above, we would
66 additional tests cases which would test each p !! 109 create additional tests cases which would each test a different property that an
67 should have as shown below: !! 110 add function should have like this:
68 111
69 .. code-block:: c 112 .. code-block:: c
70 113
71 void add_test_basic(struct kunit *test 114 void add_test_basic(struct kunit *test)
72 { 115 {
73 KUNIT_EXPECT_EQ(test, 1, add(1 116 KUNIT_EXPECT_EQ(test, 1, add(1, 0));
74 KUNIT_EXPECT_EQ(test, 2, add(1 117 KUNIT_EXPECT_EQ(test, 2, add(1, 1));
75 } 118 }
76 119
77 void add_test_negative(struct kunit *t 120 void add_test_negative(struct kunit *test)
78 { 121 {
79 KUNIT_EXPECT_EQ(test, 0, add(- 122 KUNIT_EXPECT_EQ(test, 0, add(-1, 1));
80 } 123 }
81 124
82 void add_test_max(struct kunit *test) 125 void add_test_max(struct kunit *test)
83 { 126 {
84 KUNIT_EXPECT_EQ(test, INT_MAX, 127 KUNIT_EXPECT_EQ(test, INT_MAX, add(0, INT_MAX));
85 KUNIT_EXPECT_EQ(test, -1, add( 128 KUNIT_EXPECT_EQ(test, -1, add(INT_MAX, INT_MIN));
86 } 129 }
87 130
88 void add_test_overflow(struct kunit *t 131 void add_test_overflow(struct kunit *test)
89 { 132 {
90 KUNIT_EXPECT_EQ(test, INT_MIN, 133 KUNIT_EXPECT_EQ(test, INT_MIN, add(INT_MAX, 1));
91 } 134 }
92 135
>> 136 Notice how it is immediately obvious what all the properties that we are testing
>> 137 for are.
>> 138
93 Assertions 139 Assertions
94 ~~~~~~~~~~ 140 ~~~~~~~~~~
95 141
96 An assertion is like an expectation, except th !! 142 KUnit also has the concept of an *assertion*. An assertion is just like an
97 terminates the test case if the condition is n !! 143 expectation except the assertion immediately terminates the test case if it is
98 !! 144 not satisfied.
99 .. code-block:: c <<
100 <<
101 static void test_sort(struct kunit *te <<
102 { <<
103 int *a, i, r = 1; <<
104 a = kunit_kmalloc_array(test, <<
105 KUNIT_ASSERT_NOT_ERR_OR_NULL(t <<
106 for (i = 0; i < TEST_LEN; i++) <<
107 r = (r * 725861) % 659 <<
108 a[i] = r; <<
109 } <<
110 sort(a, TEST_LEN, sizeof(*a), <<
111 for (i = 0; i < TEST_LEN-1; i+ <<
112 KUNIT_EXPECT_LE(test, <<
113 } <<
114 <<
115 In this example, we need to be able to allocat <<
116 function. So we use ``KUNIT_ASSERT_NOT_ERR_OR_ <<
117 there's an allocation error. <<
118 <<
119 .. note:: <<
120 In other test frameworks, ``ASSERT`` macros <<
121 ``return`` so they only work from the test <<
122 current kthread on failure, so you can call <<
123 <<
124 .. note:: <<
125 Warning: There is an exception to the above <<
126 in the suite's exit() function, or in the f <<
127 run when a test is shutting down, and an as <<
128 cleanup code from running, potentially lead <<
129 <<
130 Customizing error messages <<
131 -------------------------- <<
132 <<
133 Each of the ``KUNIT_EXPECT`` and ``KUNIT_ASSER <<
134 variant. These take a format string and argum <<
135 context to the automatically generated error m <<
136 <<
137 .. code-block:: c <<
138 <<
139 char some_str[41]; <<
140 generate_sha1_hex_string(some_str); <<
141 <<
142 /* Before. Not easy to tell why the te <<
143 KUNIT_EXPECT_EQ(test, strlen(some_str) <<
144 145
145 /* After. Now we see the offending str !! 146 For example:
146 KUNIT_EXPECT_EQ_MSG(test, strlen(some_ <<
147 <<
148 Alternatively, one can take full control over <<
149 ``KUNIT_FAIL()``, e.g. <<
150 147
151 .. code-block:: c 148 .. code-block:: c
152 149
153 /* Before */ !! 150 static void mock_test_do_expect_default_return(struct kunit *test)
154 KUNIT_EXPECT_EQ(test, some_setup_funct !! 151 {
155 !! 152 struct mock_test_context *ctx = test->priv;
156 /* After: full control over the failur !! 153 struct mock *mock = ctx->mock;
157 if (some_setup_function()) !! 154 int param0 = 5, param1 = -5;
158 KUNIT_FAIL(test, "Failed to se !! 155 const char *two_param_types[] = {"int", "int"};
159 !! 156 const void *two_params[] = {¶m0, ¶m1};
>> 157 const void *ret;
>> 158
>> 159 ret = mock->do_expect(mock,
>> 160 "test_printk", test_printk,
>> 161 two_param_types, two_params,
>> 162 ARRAY_SIZE(two_params));
>> 163 KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ret);
>> 164 KUNIT_EXPECT_EQ(test, -4, *((int *) ret));
>> 165 }
>> 166
>> 167 In this example, the method under test should return a pointer to a value, so
>> 168 if the pointer returned by the method is null or an errno, we don't want to
>> 169 bother continuing the test since the following expectation could crash the test
>> 170 case. `ASSERT_NOT_ERR_OR_NULL(...)` allows us to bail out of the test case if
>> 171 the appropriate conditions have not been satisfied to complete the test.
160 172
161 Test Suites 173 Test Suites
162 ~~~~~~~~~~~ 174 ~~~~~~~~~~~
163 175
164 We need many test cases covering all the unit' !! 176 Now obviously one unit test isn't very helpful; the power comes from having
165 many similar tests. In order to reduce duplica !! 177 many test cases covering all of a unit's behaviors. Consequently it is common
166 tests, most unit testing frameworks (including !! 178 to have many *similar* tests; in order to reduce duplication in these closely
167 *test suite*. A test suite is a collection of !! 179 related tests most unit testing frameworks - including KUnit - provide the
168 with optional setup and teardown functions tha !! 180 concept of a *test suite*. A *test suite* is just a collection of test cases
169 suite and/or every test case. !! 181 for a unit of code with a set up function that gets invoked before every test
170 !! 182 case and then a tear down function that gets invoked after every test case
171 .. note:: !! 183 completes.
172 A test case will only run if it is associat <<
173 184
174 For example: !! 185 Example:
175 186
176 .. code-block:: c 187 .. code-block:: c
177 188
178 static struct kunit_case example_test_ 189 static struct kunit_case example_test_cases[] = {
179 KUNIT_CASE(example_test_foo), 190 KUNIT_CASE(example_test_foo),
180 KUNIT_CASE(example_test_bar), 191 KUNIT_CASE(example_test_bar),
181 KUNIT_CASE(example_test_baz), 192 KUNIT_CASE(example_test_baz),
182 {} 193 {}
183 }; 194 };
184 195
185 static struct kunit_suite example_test 196 static struct kunit_suite example_test_suite = {
186 .name = "example", 197 .name = "example",
187 .init = example_test_init, 198 .init = example_test_init,
188 .exit = example_test_exit, 199 .exit = example_test_exit,
189 .suite_init = example_suite_in <<
190 .suite_exit = example_suite_ex <<
191 .test_cases = example_test_cas 200 .test_cases = example_test_cases,
192 }; 201 };
193 kunit_test_suite(example_test_suite); 202 kunit_test_suite(example_test_suite);
194 203
195 In the above example, the test suite ``example !! 204 In the above example the test suite, ``example_test_suite``, would run the test
196 ``example_suite_init``, then run the test case !! 205 cases ``example_test_foo``, ``example_test_bar``, and ``example_test_baz``;
197 ``example_test_bar``, and ``example_test_baz`` !! 206 each would have ``example_test_init`` called immediately before it and would
198 ``example_test_init`` called immediately befor !! 207 have ``example_test_exit`` called immediately after it.
199 called immediately after it. Finally, ``exampl !! 208 ``kunit_test_suite(example_test_suite)`` registers the test suite with the
200 after everything else. ``kunit_test_suite(exam !! 209 KUnit test framework.
201 test suite with the KUnit test framework. <<
202 210
203 .. note:: 211 .. note::
204 The ``exit`` and ``suite_exit`` functions w !! 212 A test case will only be run if it is associated with a test suite.
205 ``suite_init`` fail. Make sure that they ca <<
206 state which may result from ``init`` or ``s <<
207 or exiting early. <<
208 <<
209 ``kunit_test_suite(...)`` is a macro which tel <<
210 specified test suite in a special linker secti <<
211 either after ``late_init``, or when the test m <<
212 built as a module). <<
213 <<
214 For more information, see Documentation/dev-to <<
215 <<
216 .. _kunit-on-non-uml: <<
217 <<
218 Writing Tests For Other Architectures <<
219 ------------------------------------- <<
220 <<
221 It is better to write tests that run on UML to <<
222 particular architecture. It is better to write <<
223 another easy to obtain (and monetarily free) s <<
224 piece of hardware. <<
225 <<
226 Nevertheless, there are still valid reasons to <<
227 or hardware specific. For example, we might wa <<
228 belongs in ``arch/some-arch/*``. Even so, try <<
229 not depend on physical hardware. Some of our t <<
230 only few tests actually require the hardware t <<
231 available, instead of disabling tests, we can <<
232 <<
233 Now that we have narrowed down exactly what bi <<
234 actual procedure for writing and running the t <<
235 KUnit tests. <<
236 <<
237 .. important:: <<
238 We may have to reset hardware state. If thi <<
239 be able to run one test case per invocation <<
240 213
241 .. TODO(brendanhiggins@google.com): Add an act !! 214 ``kunit_test_suite(...)`` is a macro which tells the linker to put the specified
242 dependent KUnit test. !! 215 test suite in a special linker section so that it can be run by KUnit either
>> 216 after late_init, or when the test module is loaded (depending on whether the
>> 217 test was built in or not).
243 218
244 Common Patterns !! 219 For more information on these types of things see the :doc:`api/test`.
245 =============== <<
246 220
247 Isolating Behavior 221 Isolating Behavior
248 ------------------ !! 222 ==================
249 223
250 Unit testing limits the amount of code under t !! 224 The most important aspect of unit testing that other forms of testing do not
251 what code gets run when the unit under test ca !! 225 provide is the ability to limit the amount of code under test to a single unit.
252 is exposed as part of an API such that the def !! 226 In practice, this is only possible by being able to control what code gets run
253 changed without affecting the rest of the code !! 227 when the unit under test calls a function and this is usually accomplished
254 from two constructs: classes, which are struct !! 228 through some sort of indirection where a function is exposed as part of an API
255 provided by the implementer, and architecture- !! 229 such that the definition of that function can be changed without affecting the
256 definitions selected at compile time. !! 230 rest of the code base. In the kernel this primarily comes from two constructs,
>> 231 classes, structs that contain function pointers that are provided by the
>> 232 implementer, and architecture-specific functions which have definitions selected
>> 233 at compile time.
257 234
258 Classes 235 Classes
259 ~~~~~~~ !! 236 -------
260 237
261 Classes are not a construct that is built into 238 Classes are not a construct that is built into the C programming language;
262 however, it is an easily derived concept. Acco !! 239 however, it is an easily derived concept. Accordingly, pretty much every project
263 project that does not use a standardized objec !! 240 that does not use a standardized object oriented library (like GNOME's GObject)
264 GObject) has their own slightly different way !! 241 has their own slightly different way of doing object oriented programming; the
265 programming; the Linux kernel is no exception. !! 242 Linux kernel is no exception.
266 243
267 The central concept in kernel object oriented 244 The central concept in kernel object oriented programming is the class. In the
268 kernel, a *class* is a struct that contains fu 245 kernel, a *class* is a struct that contains function pointers. This creates a
269 contract between *implementers* and *users* si 246 contract between *implementers* and *users* since it forces them to use the
270 same function signature without having to call !! 247 same function signature without having to call the function directly. In order
271 class, the function pointers must specify that !! 248 for it to truly be a class, the function pointers must specify that a pointer
272 a *class handle*, be one of the parameters. Th !! 249 to the class, known as a *class handle*, be one of the parameters; this makes
273 known as *methods*) have access to member vari !! 250 it possible for the member functions (also known as *methods*) to have access
274 allowing the same implementation to have multi !! 251 to member variables (more commonly known as *fields*) allowing the same
275 !! 252 implementation to have multiple *instances*.
276 A class can be *overridden* by *child classes* !! 253
277 in the child class. Then when the child class !! 254 Typically a class can be *overridden* by *child classes* by embedding the
278 implementation knows that the pointer passed t !! 255 *parent class* in the child class. Then when a method provided by the child
279 within the child. Thus, the child can compute !! 256 class is called, the child implementation knows that the pointer passed to it is
280 pointer to the parent is always a fixed offset !! 257 of a parent contained within the child; because of this, the child can compute
281 This offset is the offset of the parent contai !! 258 the pointer to itself because the pointer to the parent is always a fixed offset
282 example: !! 259 from the pointer to the child; this offset is the offset of the parent contained
>> 260 in the child struct. For example:
283 261
284 .. code-block:: c 262 .. code-block:: c
285 263
286 struct shape { 264 struct shape {
287 int (*area)(struct shape *this 265 int (*area)(struct shape *this);
288 }; 266 };
289 267
290 struct rectangle { 268 struct rectangle {
291 struct shape parent; 269 struct shape parent;
292 int length; 270 int length;
293 int width; 271 int width;
294 }; 272 };
295 273
296 int rectangle_area(struct shape *this) 274 int rectangle_area(struct shape *this)
297 { 275 {
298 struct rectangle *self = conta !! 276 struct rectangle *self = container_of(this, struct shape, parent);
299 277
300 return self->length * self->wi 278 return self->length * self->width;
301 }; 279 };
302 280
303 void rectangle_new(struct rectangle *s 281 void rectangle_new(struct rectangle *self, int length, int width)
304 { 282 {
305 self->parent.area = rectangle_ 283 self->parent.area = rectangle_area;
306 self->length = length; 284 self->length = length;
307 self->width = width; 285 self->width = width;
308 } 286 }
309 287
310 In this example, computing the pointer to the !! 288 In this example (as in most kernel code) the operation of computing the pointer
311 parent is done by ``container_of``. !! 289 to the child from the pointer to the parent is done by ``container_of``.
312 290
313 Faking Classes 291 Faking Classes
314 ~~~~~~~~~~~~~~ 292 ~~~~~~~~~~~~~~
315 293
316 In order to unit test a piece of code that cal 294 In order to unit test a piece of code that calls a method in a class, the
317 behavior of the method must be controllable, o 295 behavior of the method must be controllable, otherwise the test ceases to be a
318 unit test and becomes an integration test. 296 unit test and becomes an integration test.
319 297
320 A fake class implements a piece of code that i !! 298 A fake just provides an implementation of a piece of code that is different than
321 production instance, but behaves identical fro !! 299 what runs in a production instance, but behaves identically from the standpoint
322 This is done to replace a dependency that is h !! 300 of the callers; this is usually done to replace a dependency that is hard to
323 example, implementing a fake EEPROM that store !! 301 deal with, or is slow.
324 internal buffer. Assume we have a class that r !! 302
>> 303 A good example for this might be implementing a fake EEPROM that just stores the
>> 304 "contents" in an internal buffer. For example, let's assume we have a class that
>> 305 represents an EEPROM:
325 306
326 .. code-block:: c 307 .. code-block:: c
327 308
328 struct eeprom { 309 struct eeprom {
329 ssize_t (*read)(struct eeprom 310 ssize_t (*read)(struct eeprom *this, size_t offset, char *buffer, size_t count);
330 ssize_t (*write)(struct eeprom 311 ssize_t (*write)(struct eeprom *this, size_t offset, const char *buffer, size_t count);
331 }; 312 };
332 313
333 And we want to test code that buffers writes t !! 314 And we want to test some code that buffers writes to the EEPROM:
334 315
335 .. code-block:: c 316 .. code-block:: c
336 317
337 struct eeprom_buffer { 318 struct eeprom_buffer {
338 ssize_t (*write)(struct eeprom 319 ssize_t (*write)(struct eeprom_buffer *this, const char *buffer, size_t count);
339 int flush(struct eeprom_buffer 320 int flush(struct eeprom_buffer *this);
340 size_t flush_count; /* Flushes 321 size_t flush_count; /* Flushes when buffer exceeds flush_count. */
341 }; 322 };
342 323
343 struct eeprom_buffer *new_eeprom_buffe 324 struct eeprom_buffer *new_eeprom_buffer(struct eeprom *eeprom);
344 void destroy_eeprom_buffer(struct eepr 325 void destroy_eeprom_buffer(struct eeprom *eeprom);
345 326
346 We can test this code by *faking out* the unde !! 327 We can easily test this code by *faking out* the underlying EEPROM:
347 328
348 .. code-block:: c 329 .. code-block:: c
349 330
350 struct fake_eeprom { 331 struct fake_eeprom {
351 struct eeprom parent; 332 struct eeprom parent;
352 char contents[FAKE_EEPROM_CONT 333 char contents[FAKE_EEPROM_CONTENTS_SIZE];
353 }; 334 };
354 335
355 ssize_t fake_eeprom_read(struct eeprom 336 ssize_t fake_eeprom_read(struct eeprom *parent, size_t offset, char *buffer, size_t count)
356 { 337 {
357 struct fake_eeprom *this = con 338 struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
358 339
359 count = min(count, FAKE_EEPROM 340 count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset);
360 memcpy(buffer, this->contents 341 memcpy(buffer, this->contents + offset, count);
361 342
362 return count; 343 return count;
363 } 344 }
364 345
365 ssize_t fake_eeprom_write(struct eepro 346 ssize_t fake_eeprom_write(struct eeprom *parent, size_t offset, const char *buffer, size_t count)
366 { 347 {
367 struct fake_eeprom *this = con 348 struct fake_eeprom *this = container_of(parent, struct fake_eeprom, parent);
368 349
369 count = min(count, FAKE_EEPROM 350 count = min(count, FAKE_EEPROM_CONTENTS_SIZE - offset);
370 memcpy(this->contents + offset 351 memcpy(this->contents + offset, buffer, count);
371 352
372 return count; 353 return count;
373 } 354 }
374 355
375 void fake_eeprom_init(struct fake_eepr 356 void fake_eeprom_init(struct fake_eeprom *this)
376 { 357 {
377 this->parent.read = fake_eepro 358 this->parent.read = fake_eeprom_read;
378 this->parent.write = fake_eepr 359 this->parent.write = fake_eeprom_write;
379 memset(this->contents, 0, FAKE 360 memset(this->contents, 0, FAKE_EEPROM_CONTENTS_SIZE);
380 } 361 }
381 362
382 We can now use it to test ``struct eeprom_buff 363 We can now use it to test ``struct eeprom_buffer``:
383 364
384 .. code-block:: c 365 .. code-block:: c
385 366
386 struct eeprom_buffer_test { 367 struct eeprom_buffer_test {
387 struct fake_eeprom *fake_eepro 368 struct fake_eeprom *fake_eeprom;
388 struct eeprom_buffer *eeprom_b 369 struct eeprom_buffer *eeprom_buffer;
389 }; 370 };
390 371
391 static void eeprom_buffer_test_does_no 372 static void eeprom_buffer_test_does_not_write_until_flush(struct kunit *test)
392 { 373 {
393 struct eeprom_buffer_test *ctx 374 struct eeprom_buffer_test *ctx = test->priv;
394 struct eeprom_buffer *eeprom_b 375 struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
395 struct fake_eeprom *fake_eepro 376 struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
396 char buffer[] = {0xff}; 377 char buffer[] = {0xff};
397 378
398 eeprom_buffer->flush_count = S 379 eeprom_buffer->flush_count = SIZE_MAX;
399 380
400 eeprom_buffer->write(eeprom_bu 381 eeprom_buffer->write(eeprom_buffer, buffer, 1);
401 KUNIT_EXPECT_EQ(test, fake_eep 382 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
402 383
403 eeprom_buffer->write(eeprom_bu 384 eeprom_buffer->write(eeprom_buffer, buffer, 1);
404 KUNIT_EXPECT_EQ(test, fake_eep 385 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0);
405 386
406 eeprom_buffer->flush(eeprom_bu 387 eeprom_buffer->flush(eeprom_buffer);
407 KUNIT_EXPECT_EQ(test, fake_eep 388 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
408 KUNIT_EXPECT_EQ(test, fake_eep 389 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
409 } 390 }
410 391
411 static void eeprom_buffer_test_flushes 392 static void eeprom_buffer_test_flushes_after_flush_count_met(struct kunit *test)
412 { 393 {
413 struct eeprom_buffer_test *ctx 394 struct eeprom_buffer_test *ctx = test->priv;
414 struct eeprom_buffer *eeprom_b 395 struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
415 struct fake_eeprom *fake_eepro 396 struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
416 char buffer[] = {0xff}; 397 char buffer[] = {0xff};
417 398
418 eeprom_buffer->flush_count = 2 399 eeprom_buffer->flush_count = 2;
419 400
420 eeprom_buffer->write(eeprom_bu 401 eeprom_buffer->write(eeprom_buffer, buffer, 1);
421 KUNIT_EXPECT_EQ(test, fake_eep 402 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
422 403
423 eeprom_buffer->write(eeprom_bu 404 eeprom_buffer->write(eeprom_buffer, buffer, 1);
424 KUNIT_EXPECT_EQ(test, fake_eep 405 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
425 KUNIT_EXPECT_EQ(test, fake_eep 406 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
426 } 407 }
427 408
428 static void eeprom_buffer_test_flushes 409 static void eeprom_buffer_test_flushes_increments_of_flush_count(struct kunit *test)
429 { 410 {
430 struct eeprom_buffer_test *ctx 411 struct eeprom_buffer_test *ctx = test->priv;
431 struct eeprom_buffer *eeprom_b 412 struct eeprom_buffer *eeprom_buffer = ctx->eeprom_buffer;
432 struct fake_eeprom *fake_eepro 413 struct fake_eeprom *fake_eeprom = ctx->fake_eeprom;
433 char buffer[] = {0xff, 0xff}; 414 char buffer[] = {0xff, 0xff};
434 415
435 eeprom_buffer->flush_count = 2 416 eeprom_buffer->flush_count = 2;
436 417
437 eeprom_buffer->write(eeprom_bu 418 eeprom_buffer->write(eeprom_buffer, buffer, 1);
438 KUNIT_EXPECT_EQ(test, fake_eep 419 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0);
439 420
440 eeprom_buffer->write(eeprom_bu 421 eeprom_buffer->write(eeprom_buffer, buffer, 2);
441 KUNIT_EXPECT_EQ(test, fake_eep 422 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[0], 0xff);
442 KUNIT_EXPECT_EQ(test, fake_eep 423 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[1], 0xff);
443 /* Should have only flushed th 424 /* Should have only flushed the first two bytes. */
444 KUNIT_EXPECT_EQ(test, fake_eep 425 KUNIT_EXPECT_EQ(test, fake_eeprom->contents[2], 0);
445 } 426 }
446 427
447 static int eeprom_buffer_test_init(str 428 static int eeprom_buffer_test_init(struct kunit *test)
448 { 429 {
449 struct eeprom_buffer_test *ctx 430 struct eeprom_buffer_test *ctx;
450 431
451 ctx = kunit_kzalloc(test, size 432 ctx = kunit_kzalloc(test, sizeof(*ctx), GFP_KERNEL);
452 KUNIT_ASSERT_NOT_ERR_OR_NULL(t 433 KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx);
453 434
454 ctx->fake_eeprom = kunit_kzall 435 ctx->fake_eeprom = kunit_kzalloc(test, sizeof(*ctx->fake_eeprom), GFP_KERNEL);
455 KUNIT_ASSERT_NOT_ERR_OR_NULL(t 436 KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->fake_eeprom);
456 fake_eeprom_init(ctx->fake_eep 437 fake_eeprom_init(ctx->fake_eeprom);
457 438
458 ctx->eeprom_buffer = new_eepro 439 ctx->eeprom_buffer = new_eeprom_buffer(&ctx->fake_eeprom->parent);
459 KUNIT_ASSERT_NOT_ERR_OR_NULL(t 440 KUNIT_ASSERT_NOT_ERR_OR_NULL(test, ctx->eeprom_buffer);
460 441
461 test->priv = ctx; 442 test->priv = ctx;
462 443
463 return 0; 444 return 0;
464 } 445 }
465 446
466 static void eeprom_buffer_test_exit(st 447 static void eeprom_buffer_test_exit(struct kunit *test)
467 { 448 {
468 struct eeprom_buffer_test *ctx 449 struct eeprom_buffer_test *ctx = test->priv;
469 450
470 destroy_eeprom_buffer(ctx->eep 451 destroy_eeprom_buffer(ctx->eeprom_buffer);
471 } 452 }
472 453
473 Testing Against Multiple Inputs !! 454 .. _kunit-on-non-uml:
474 ------------------------------- <<
475 <<
476 Testing just a few inputs is not enough to ens <<
477 for example: testing a hash function. <<
478 <<
479 We can write a helper macro or function. The f <<
480 For example, to test ``sha1sum(1)``, we can wr <<
481 <<
482 .. code-block:: c <<
483 <<
484 #define TEST_SHA1(in, want) \ <<
485 sha1sum(in, out); \ <<
486 KUNIT_EXPECT_STREQ_MSG(test, o <<
487 <<
488 char out[40]; <<
489 TEST_SHA1("hello world", "2aae6c35c94 <<
490 TEST_SHA1("hello world!", "430ce34d020 <<
491 <<
492 Note the use of the ``_MSG`` version of ``KUNI <<
493 detailed error and make the assertions clearer <<
494 <<
495 The ``_MSG`` variants are useful when the same <<
496 times (in a loop or helper function) and thus <<
497 identify what failed, as shown below. <<
498 <<
499 In complicated cases, we recommend using a *ta <<
500 helper macro variation, for example: <<
501 <<
502 .. code-block:: c <<
503 <<
504 int i; <<
505 char out[40]; <<
506 <<
507 struct sha1_test_case { <<
508 const char *str; <<
509 const char *sha1; <<
510 }; <<
511 <<
512 struct sha1_test_case cases[] = { <<
513 { <<
514 .str = "hello world", <<
515 .sha1 = "2aae6c35c94fc <<
516 }, <<
517 { <<
518 .str = "hello world!", <<
519 .sha1 = "430ce34d02072 <<
520 }, <<
521 }; <<
522 for (i = 0; i < ARRAY_SIZE(cases); ++i <<
523 sha1sum(cases[i].str, out); <<
524 KUNIT_EXPECT_STREQ_MSG(test, o <<
525 "sha1sum <<
526 } <<
527 <<
528 <<
529 There is more boilerplate code involved, but i <<
530 <<
531 * be more readable when there are multiple inp <<
532 <<
533 * For example, see ``fs/ext4/inode-test.c``. <<
534 <<
535 * reduce duplication if test cases are shared <<
536 <<
537 * For example: if we want to test ``sha256su <<
538 field and reuse ``cases``. <<
539 <<
540 * be converted to a "parameterized test". <<
541 <<
542 Parameterized Testing <<
543 ~~~~~~~~~~~~~~~~~~~~~ <<
544 <<
545 The table-driven testing pattern is common eno <<
546 support for it. <<
547 <<
548 By reusing the same ``cases`` array from above <<
549 "parameterized test" with the following. <<
550 <<
551 .. code-block:: c <<
552 <<
553 // This is copy-pasted from above. <<
554 struct sha1_test_case { <<
555 const char *str; <<
556 const char *sha1; <<
557 }; <<
558 const struct sha1_test_case cases[] = <<
559 { <<
560 .str = "hello world", <<
561 .sha1 = "2aae6c35c94fc <<
562 }, <<
563 { <<
564 .str = "hello world!", <<
565 .sha1 = "430ce34d02072 <<
566 }, <<
567 }; <<
568 <<
569 // Creates `sha1_gen_params()` to iter <<
570 // the struct member `str` for the cas <<
571 KUNIT_ARRAY_PARAM_DESC(sha1, cases, st <<
572 <<
573 // Looks no different from a normal te <<
574 static void sha1_test(struct kunit *te <<
575 { <<
576 // This function can just cont <<
577 // The former `cases[i]` is ac <<
578 char out[40]; <<
579 struct sha1_test_case *test_pa <<
580 <<
581 sha1sum(test_param->str, out); <<
582 KUNIT_EXPECT_STREQ_MSG(test, o <<
583 "sha1sum <<
584 } <<
585 <<
586 // Instead of KUNIT_CASE, we use KUNIT <<
587 // function declared by KUNIT_ARRAY_PA <<
588 static struct kunit_case sha1_test_cas <<
589 KUNIT_CASE_PARAM(sha1_test, sh <<
590 {} <<
591 }; <<
592 <<
593 Allocating Memory <<
594 ----------------- <<
595 <<
596 Where you might use ``kzalloc``, you can inste <<
597 will then ensure that the memory is freed once <<
598 <<
599 This is useful because it lets us use the ``KU <<
600 early from a test without having to worry abou <<
601 For example: <<
602 <<
603 .. code-block:: c <<
604 <<
605 void example_test_allocation(struct ku <<
606 { <<
607 char *buffer = kunit_kzalloc(t <<
608 /* Ensure allocation succeeded <<
609 KUNIT_ASSERT_NOT_ERR_OR_NULL(t <<
610 <<
611 KUNIT_ASSERT_STREQ(test, buffe <<
612 } <<
613 <<
614 Registering Cleanup Actions <<
615 --------------------------- <<
616 <<
617 If you need to perform some cleanup beyond sim <<
618 you can register a custom "deferred action", w <<
619 run when the test exits (whether cleanly, or v <<
620 <<
621 Actions are simple functions with no return va <<
622 context argument, and fulfill the same role as <<
623 and Go tests, "defer" statements in languages <<
624 (in some cases) destructors in RAII languages. <<
625 <<
626 These are very useful for unregistering things <<
627 files or other resources, or freeing resources <<
628 <<
629 For example: <<
630 <<
631 .. code-block:: C <<
632 <<
633 static void cleanup_device(void *ctx) <<
634 { <<
635 struct device *dev = (struct d <<
636 <<
637 device_unregister(dev); <<
638 } <<
639 <<
640 void example_device_test(struct kunit <<
641 { <<
642 struct my_device dev; <<
643 <<
644 device_register(&dev); <<
645 <<
646 kunit_add_action(test, &cleanu <<
647 } <<
648 <<
649 Note that, for functions like device_unregiste <<
650 pointer-sized argument, it's possible to autom <<
651 with the ``KUNIT_DEFINE_ACTION_WRAPPER()`` mac <<
652 <<
653 .. code-block:: C <<
654 <<
655 KUNIT_DEFINE_ACTION_WRAPPER(device_unr <<
656 kunit_add_action(test, &device_unregis <<
657 <<
658 You should do this in preference to manually c <<
659 as casting function pointers will break Contro <<
660 <<
661 ``kunit_add_action`` can fail if, for example, <<
662 You can use ``kunit_add_action_or_reset`` inst <<
663 immediately if it cannot be deferred. <<
664 <<
665 If you need more control over when the cleanup <<
666 can trigger it early using ``kunit_release_act <<
667 with ``kunit_remove_action``. <<
668 <<
669 <<
670 Testing Static Functions <<
671 ------------------------ <<
672 <<
673 If we do not want to expose functions or varia <<
674 conditionally export the used symbol. For exam <<
675 <<
676 .. code-block:: c <<
677 <<
678 /* In my_file.c */ <<
679 455
680 VISIBLE_IF_KUNIT int do_interesting_th !! 456 KUnit on non-UML architectures
681 EXPORT_SYMBOL_IF_KUNIT(do_interesting_ !! 457 ==============================
682 458
683 /* In my_file.h */ !! 459 By default KUnit uses UML as a way to provide dependencies for code under test.
>> 460 Under most circumstances KUnit's usage of UML should be treated as an
>> 461 implementation detail of how KUnit works under the hood. Nevertheless, there
>> 462 are instances where being able to run architecture-specific code or test
>> 463 against real hardware is desirable. For these reasons KUnit supports running on
>> 464 other architectures.
684 465
685 #if IS_ENABLED(CONFIG_KUNIT) !! 466 Running existing KUnit tests on non-UML architectures
686 int do_interesting_thing(void) !! 467 -----------------------------------------------------
687 #endif <<
688 468
689 Alternatively, you could conditionally ``#incl !! 469 There are some special considerations when running existing KUnit tests on
690 your .c file. For example: !! 470 non-UML architectures:
691 471
692 .. code-block:: c !! 472 * Hardware may not be deterministic, so a test that always passes or fails
>> 473 when run under UML may not always do so on real hardware.
>> 474 * Hardware and VM environments may not be hermetic. KUnit tries its best to
>> 475 provide a hermetic environment to run tests; however, it cannot manage state
>> 476 that it doesn't know about outside of the kernel. Consequently, tests that
>> 477 may be hermetic on UML may not be hermetic on other architectures.
>> 478 * Some features and tooling may not be supported outside of UML.
>> 479 * Hardware and VMs are slower than UML.
693 480
694 /* In my_file.c */ !! 481 None of these are reasons not to run your KUnit tests on real hardware; they are
>> 482 only things to be aware of when doing so.
695 483
696 static int do_interesting_thing(); !! 484 The biggest impediment will likely be that certain KUnit features and
>> 485 infrastructure may not support your target environment. For example, at this
>> 486 time the KUnit Wrapper (``tools/testing/kunit/kunit.py``) does not work outside
>> 487 of UML. Unfortunately, there is no way around this. Using UML (or even just a
>> 488 particular architecture) allows us to make a lot of assumptions that make it
>> 489 possible to do things which might otherwise be impossible.
697 490
698 #ifdef CONFIG_MY_KUNIT_TEST !! 491 Nevertheless, all core KUnit framework features are fully supported on all
699 #include "my_kunit_test.c" !! 492 architectures, and using them is straightforward: all you need to do is to take
700 #endif !! 493 your kunitconfig, your Kconfig options for the tests you would like to run, and
>> 494 merge them into whatever config your are using for your platform. That's it!
701 495
702 Injecting Test-Only Code !! 496 For example, let's say you have the following kunitconfig:
703 ------------------------ <<
704 497
705 Similar to as shown above, we can add test-spe !! 498 .. code-block:: none
706 499
707 .. code-block:: c !! 500 CONFIG_KUNIT=y
>> 501 CONFIG_KUNIT_EXAMPLE_TEST=y
708 502
709 /* In my_file.h */ !! 503 If you wanted to run this test on an x86 VM, you might add the following config
>> 504 options to your ``.config``:
710 505
711 #ifdef CONFIG_MY_KUNIT_TEST !! 506 .. code-block:: none
712 /* Defined in my_kunit_test.c */ <<
713 void test_only_hook(void); <<
714 #else <<
715 void test_only_hook(void) { } <<
716 #endif <<
717 <<
718 This test-only code can be made more useful by <<
719 as shown in next section: *Accessing The Curre <<
720 <<
721 Accessing The Current Test <<
722 -------------------------- <<
723 <<
724 In some cases, we need to call test-only code <<
725 is helpful, for example, when providing a fake <<
726 to fail any current test from within an error <<
727 We can do this via the ``kunit_test`` field in <<
728 access using the ``kunit_get_current_test()`` <<
729 <<
730 ``kunit_get_current_test()`` is safe to call e <<
731 KUnit is not enabled, or if no test is running <<
732 return ``NULL``. This compiles down to either <<
733 so will have a negligible performance impact w <<
734 507
735 The example below uses this to implement a "mo !! 508 CONFIG_KUNIT=y
>> 509 CONFIG_KUNIT_EXAMPLE_TEST=y
>> 510 CONFIG_SERIAL_8250=y
>> 511 CONFIG_SERIAL_8250_CONSOLE=y
736 512
737 .. code-block:: c !! 513 All these new options do is enable support for a common serial console needed
>> 514 for logging.
738 515
739 #include <kunit/test-bug.h> /* for kun !! 516 Next, you could build a kernel with these tests as follows:
740 517
741 struct test_data { <<
742 int foo_result; <<
743 int want_foo_called_with; <<
744 }; <<
745 518
746 static int fake_foo(int arg) !! 519 .. code-block:: bash
747 { <<
748 struct kunit *test = kunit_get <<
749 struct test_data *test_data = <<
750 520
751 KUNIT_EXPECT_EQ(test, test_dat !! 521 make ARCH=x86 olddefconfig
752 return test_data->foo_result; !! 522 make ARCH=x86
753 } <<
754 523
755 static void example_simple_test(struct !! 524 Once you have built a kernel, you could run it on QEMU as follows:
756 { <<
757 /* Assume priv (private, a mem <<
758 * the init function) is alloc <<
759 struct test_data *test_data = <<
760 525
761 test_data->foo_result = 42; !! 526 .. code-block:: bash
762 test_data->want_foo_called_wit <<
763 527
764 /* In a real test, we'd probab !! 528 qemu-system-x86_64 -enable-kvm \
765 * like an ops struct, etc. in !! 529 -m 1024 \
766 KUNIT_EXPECT_EQ(test, fake_foo !! 530 -kernel arch/x86_64/boot/bzImage \
767 } !! 531 -append 'console=ttyS0' \
>> 532 --nographic
768 533
769 In this example, we are using the ``priv`` mem !! 534 Interspersed in the kernel logs you might see the following:
770 of passing data to the test from the init func <<
771 pointer that can be used for any user data. Th <<
772 variables, as it avoids concurrency issues. <<
773 535
774 Had we wanted something more flexible, we coul !! 536 .. code-block:: none
775 Each test can have multiple resources which ha <<
776 flexibility as a ``priv`` member, but also, fo <<
777 functions to create resources without conflict <<
778 possible to define a clean up function for eac <<
779 avoid resource leaks. For more information, se <<
780 537
781 Failing The Current Test !! 538 TAP version 14
782 ------------------------ !! 539 # Subtest: example
>> 540 1..1
>> 541 # example_simple_test: initializing
>> 542 ok 1 - example_simple_test
>> 543 ok 1 - example
783 544
784 If we want to fail the current test, we can us !! 545 Congratulations, you just ran a KUnit test on the x86 architecture!
785 which is defined in ``<kunit/test-bug.h>`` and <<
786 For example, we have an option to enable some <<
787 structures as shown below: <<
788 546
789 .. code-block:: c !! 547 In a similar manner, kunit and kunit tests can also be built as modules,
>> 548 so if you wanted to run tests in this way you might add the following config
>> 549 options to your ``.config``:
790 550
791 #include <kunit/test-bug.h> !! 551 .. code-block:: none
792 552
793 #ifdef CONFIG_EXTRA_DEBUG_CHECKS !! 553 CONFIG_KUNIT=m
794 static void validate_my_data(struct da !! 554 CONFIG_KUNIT_EXAMPLE_TEST=m
795 { <<
796 if (is_valid(data)) <<
797 return; <<
798 555
799 kunit_fail_current_test("data !! 556 Once the kernel is built and installed, a simple
800 <<
801 /* Normal, non-KUnit, error re <<
802 } <<
803 #else <<
804 static void my_debug_function(void) { <<
805 #endif <<
806 <<
807 ``kunit_fail_current_test()`` is safe to call <<
808 KUnit is not enabled, or if no test is running <<
809 nothing. This compiles down to either a no-op <<
810 have a negligible performance impact when no t <<
811 <<
812 Managing Fake Devices and Drivers <<
813 --------------------------------- <<
814 <<
815 When testing drivers or code which interacts w <<
816 require a ``struct device`` or ``struct device <<
817 up a real device is not required to test any g <<
818 can be used instead. <<
819 <<
820 KUnit provides helper functions to create and <<
821 are internally of type ``struct kunit_device`` <<
822 ``kunit_bus``. These devices support managed d <<
823 described in Documentation/driver-api/driver-m <<
824 <<
825 To create a KUnit-managed ``struct device_driv <<
826 which will create a driver with the given name <<
827 will automatically be destroyed when the corre <<
828 be manually destroyed with ``driver_unregister <<
829 <<
830 To create a fake device, use the ``kunit_devic <<
831 and register a device, using a new KUnit-manag <<
832 To provide a specific, non-KUnit-managed drive <<
833 instead. Like with managed drivers, KUnit-mana <<
834 cleaned up when the test finishes, but can be <<
835 ``kunit_device_unregister()``. <<
836 <<
837 The KUnit devices should be used in preference <<
838 instead of ``platform_device_register()`` in c <<
839 a platform device. <<
840 557
841 For example: !! 558 .. code-block:: bash
842 559
843 .. code-block:: c !! 560 modprobe example-test
844 561
845 #include <kunit/device.h> !! 562 ...will run the tests.
846 563
847 static void test_my_device(struct kuni !! 564 .. note::
848 { !! 565 Note that you should make sure your test depends on ``KUNIT=y`` in Kconfig
849 struct device *fake_device; !! 566 if the test does not support module build. Otherwise, it will trigger
850 const char *dev_managed_string !! 567 compile errors if ``CONFIG_KUNIT`` is ``m``.
>> 568
>> 569 Writing new tests for other architectures
>> 570 -----------------------------------------
>> 571
>> 572 The first thing you must do is ask yourself whether it is necessary to write a
>> 573 KUnit test for a specific architecture, and then whether it is necessary to
>> 574 write that test for a particular piece of hardware. In general, writing a test
>> 575 that depends on having access to a particular piece of hardware or software (not
>> 576 included in the Linux source repo) should be avoided at all costs.
>> 577
>> 578 Even if you only ever plan on running your KUnit test on your hardware
>> 579 configuration, other people may want to run your tests and may not have access
>> 580 to your hardware. If you write your test to run on UML, then anyone can run your
>> 581 tests without knowing anything about your particular setup, and you can still
>> 582 run your tests on your hardware setup just by compiling for your architecture.
851 583
852 // Create a fake device. !! 584 .. important::
853 fake_device = kunit_device_reg !! 585 Always prefer tests that run on UML to tests that only run under a particular
854 KUNIT_ASSERT_NOT_ERR_OR_NULL(t !! 586 architecture, and always prefer tests that run under QEMU or another easy
>> 587 (and monetarily free) to obtain software environment to a specific piece of
>> 588 hardware.
>> 589
>> 590 Nevertheless, there are still valid reasons to write an architecture or hardware
>> 591 specific test: for example, you might want to test some code that really belongs
>> 592 in ``arch/some-arch/*``. Even so, try your best to write the test so that it
>> 593 does not depend on physical hardware: if some of your test cases don't need the
>> 594 hardware, only require the hardware for tests that actually need it.
>> 595
>> 596 Now that you have narrowed down exactly what bits are hardware specific, the
>> 597 actual procedure for writing and running the tests is pretty much the same as
>> 598 writing normal KUnit tests. One special caveat is that you have to reset
>> 599 hardware state in between test cases; if this is not possible, you may only be
>> 600 able to run one test case per invocation.
855 601
856 // Pass it to functions which !! 602 .. TODO(brendanhiggins@google.com): Add an actual example of an architecture-
857 dev_managed_string = devm_kstr !! 603 dependent KUnit test.
858 604
859 // Everything is cleaned up au !! 605 KUnit debugfs representation
860 } !! 606 ============================
>> 607 When kunit test suites are initialized, they create an associated directory
>> 608 in ``/sys/kernel/debug/kunit/<test-suite>``. The directory contains one file
>> 609
>> 610 - results: "cat results" displays results of each test case and the results
>> 611 of the entire suite for the last test run.
>> 612
>> 613 The debugfs representation is primarily of use when kunit test suites are
>> 614 run in a native environment, either as modules or builtin. Having a way
>> 615 to display results like this is valuable as otherwise results can be
>> 616 intermixed with other events in dmesg output. The maximum size of each
>> 617 results file is KUNIT_LOG_SIZE bytes (defined in ``include/kunit/test.h``).
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