yaml-cpp

primer.md (23671B)

---

 # Googletest Primer
 
 ## Introduction: Why googletest?
 
 *googletest* helps you write better C++ tests.
 
 googletest is a testing framework developed by the Testing Technology team with
 Google's specific requirements and constraints in mind. Whether you work on
 Linux, Windows, or a Mac, if you write C++ code, googletest can help you. And it
 supports *any* kind of tests, not just unit tests.
 
 So what makes a good test, and how does googletest fit in? We believe:
 
 1.  Tests should be *independent* and *repeatable*. It's a pain to debug a test
     that succeeds or fails as a result of other tests. googletest isolates the
     tests by running each of them on a different object. When a test fails,
     googletest allows you to run it in isolation for quick debugging.
 2.  Tests should be well *organized* and reflect the structure of the tested
     code. googletest groups related tests into test suites that can share data
     and subroutines. This common pattern is easy to recognize and makes tests
     easy to maintain. Such consistency is especially helpful when people switch
     projects and start to work on a new code base.
 3.  Tests should be *portable* and *reusable*. Google has a lot of code that is
     platform-neutral; its tests should also be platform-neutral. googletest
     works on different OSes, with different compilers, with or without
     exceptions, so googletest tests can work with a variety of configurations.
 4.  When tests fail, they should provide as much *information* about the problem
     as possible. googletest doesn't stop at the first test failure. Instead, it
     only stops the current test and continues with the next. You can also set up
     tests that report non-fatal failures after which the current test continues.
     Thus, you can detect and fix multiple bugs in a single run-edit-compile
     cycle.
 5.  The testing framework should liberate test writers from housekeeping chores
     and let them focus on the test *content*. googletest automatically keeps
     track of all tests defined, and doesn't require the user to enumerate them
     in order to run them.
 6.  Tests should be *fast*. With googletest, you can reuse shared resources
     across tests and pay for the set-up/tear-down only once, without making
     tests depend on each other.
 
 Since googletest is based on the popular xUnit architecture, you'll feel right
 at home if you've used JUnit or PyUnit before. If not, it will take you about 10
 minutes to learn the basics and get started. So let's go!
 
 ## Beware of the nomenclature
 
 _Note:_ There might be some confusion arising from different definitions of the
 terms _Test_, _Test Case_ and _Test Suite_, so beware of misunderstanding these.
 
 Historically, googletest started to use the term _Test Case_ for grouping
 related tests, whereas current publications, including International Software
 Testing Qualifications Board ([ISTQB](http://www.istqb.org/)) materials and
 various textbooks on software quality, use the term
 _[Test Suite][istqb test suite]_ for this.
 
 The related term _Test_, as it is used in googletest, corresponds to the term
 _[Test Case][istqb test case]_ of ISTQB and others.
 
 The term _Test_ is commonly of broad enough sense, including ISTQB's definition
 of _Test Case_, so it's not much of a problem here. But the term _Test Case_ as
 was used in Google Test is of contradictory sense and thus confusing.
 
 googletest recently started replacing the term _Test Case_ with _Test Suite_.
 The preferred API is *TestSuite*. The older TestCase API is being slowly
 deprecated and refactored away.
 
 So please be aware of the different definitions of the terms:
 
 <!-- mdformat off(github rendering does not support multiline tables) -->
 
 Meaning                                                                              | googletest Term         | [ISTQB](http://www.istqb.org/) Term
 :----------------------------------------------------------------------------------- | :---------------------- | :----------------------------------
 Exercise a particular program path with specific input values and verify the results | [TEST()](#simple-tests) | [Test Case][istqb test case]
 
 <!-- mdformat on -->
 
 [istqb test case]: http://glossary.istqb.org/en/search/test%20case
 [istqb test suite]: http://glossary.istqb.org/en/search/test%20suite
 
 ## Basic Concepts
 
 When using googletest, you start by writing *assertions*, which are statements
 that check whether a condition is true. An assertion's result can be *success*,
 *nonfatal failure*, or *fatal failure*. If a fatal failure occurs, it aborts the
 current function; otherwise the program continues normally.
 
 *Tests* use assertions to verify the tested code's behavior. If a test crashes
 or has a failed assertion, then it *fails*; otherwise it *succeeds*.
 
 A *test suite* contains one or many tests. You should group your tests into test
 suites that reflect the structure of the tested code. When multiple tests in a
 test suite need to share common objects and subroutines, you can put them into a
 *test fixture* class.
 
 A *test program* can contain multiple test suites.
 
 We'll now explain how to write a test program, starting at the individual
 assertion level and building up to tests and test suites.
 
 ## Assertions
 
 googletest assertions are macros that resemble function calls. You test a class
 or function by making assertions about its behavior. When an assertion fails,
 googletest prints the assertion's source file and line number location, along
 with a failure message. You may also supply a custom failure message which will
 be appended to googletest's message.
 
 The assertions come in pairs that test the same thing but have different effects
 on the current function. `ASSERT_*` versions generate fatal failures when they
 fail, and **abort the current function**. `EXPECT_*` versions generate nonfatal
 failures, which don't abort the current function. Usually `EXPECT_*` are
 preferred, as they allow more than one failure to be reported in a test.
 However, you should use `ASSERT_*` if it doesn't make sense to continue when the
 assertion in question fails.
 
 Since a failed `ASSERT_*` returns from the current function immediately,
 possibly skipping clean-up code that comes after it, it may cause a space leak.
 Depending on the nature of the leak, it may or may not be worth fixing - so keep
 this in mind if you get a heap checker error in addition to assertion errors.
 
 To provide a custom failure message, simply stream it into the macro using the
 `<<` operator or a sequence of such operators. An example:
 
 ```c++
 ASSERT_EQ(x.size(), y.size()) << "Vectors x and y are of unequal length";
 
 for (int i = 0; i < x.size(); ++i) {
   EXPECT_EQ(x[i], y[i]) << "Vectors x and y differ at index " << i;
 }
 ```
 
 Anything that can be streamed to an `ostream` can be streamed to an assertion
 macro--in particular, C strings and `string` objects. If a wide string
 (`wchar_t*`, `TCHAR*` in `UNICODE` mode on Windows, or `std::wstring`) is
 streamed to an assertion, it will be translated to UTF-8 when printed.
 
 ### Basic Assertions
 
 These assertions do basic true/false condition testing.
 
 Fatal assertion            | Nonfatal assertion         | Verifies
 -------------------------- | -------------------------- | --------------------
 `ASSERT_TRUE(condition);`  | `EXPECT_TRUE(condition);`  | `condition` is true
 `ASSERT_FALSE(condition);` | `EXPECT_FALSE(condition);` | `condition` is false
 
 Remember, when they fail, `ASSERT_*` yields a fatal failure and returns from the
 current function, while `EXPECT_*` yields a nonfatal failure, allowing the
 function to continue running. In either case, an assertion failure means its
 containing test fails.
 
 **Availability**: Linux, Windows, Mac.
 
 ### Binary Comparison
 
 This section describes assertions that compare two values.
 
 Fatal assertion          | Nonfatal assertion       | Verifies
 ------------------------ | ------------------------ | --------------
 `ASSERT_EQ(val1, val2);` | `EXPECT_EQ(val1, val2);` | `val1 == val2`
 `ASSERT_NE(val1, val2);` | `EXPECT_NE(val1, val2);` | `val1 != val2`
 `ASSERT_LT(val1, val2);` | `EXPECT_LT(val1, val2);` | `val1 < val2`
 `ASSERT_LE(val1, val2);` | `EXPECT_LE(val1, val2);` | `val1 <= val2`
 `ASSERT_GT(val1, val2);` | `EXPECT_GT(val1, val2);` | `val1 > val2`
 `ASSERT_GE(val1, val2);` | `EXPECT_GE(val1, val2);` | `val1 >= val2`
 
 Value arguments must be comparable by the assertion's comparison operator or
 you'll get a compiler error. We used to require the arguments to support the
 `<<` operator for streaming to an `ostream`, but this is no longer necessary. If
 `<<` is supported, it will be called to print the arguments when the assertion
 fails; otherwise googletest will attempt to print them in the best way it can.
 For more details and how to customize the printing of the arguments, see the
 [documentation](../../googlemock/docs/cook_book.md#teaching-gmock-how-to-print-your-values).
 
 These assertions can work with a user-defined type, but only if you define the
 corresponding comparison operator (e.g., `==` or `<`). Since this is discouraged
 by the Google
 [C++ Style Guide](https://google.github.io/styleguide/cppguide.html#Operator_Overloading),
 you may need to use `ASSERT_TRUE()` or `EXPECT_TRUE()` to assert the equality of
 two objects of a user-defined type.
 
 However, when possible, `ASSERT_EQ(actual, expected)` is preferred to
 `ASSERT_TRUE(actual == expected)`, since it tells you `actual` and `expected`'s
 values on failure.
 
 Arguments are always evaluated exactly once. Therefore, it's OK for the
 arguments to have side effects. However, as with any ordinary C/C++ function,
 the arguments' evaluation order is undefined (i.e., the compiler is free to
 choose any order), and your code should not depend on any particular argument
 evaluation order.
 
 `ASSERT_EQ()` does pointer equality on pointers. If used on two C strings, it
 tests if they are in the same memory location, not if they have the same value.
 Therefore, if you want to compare C strings (e.g. `const char*`) by value, use
 `ASSERT_STREQ()`, which will be described later on. In particular, to assert
 that a C string is `NULL`, use `ASSERT_STREQ(c_string, NULL)`. Consider using
 `ASSERT_EQ(c_string, nullptr)` if c++11 is supported. To compare two `string`
 objects, you should use `ASSERT_EQ`.
 
 When doing pointer comparisons use `*_EQ(ptr, nullptr)` and `*_NE(ptr, nullptr)`
 instead of `*_EQ(ptr, NULL)` and `*_NE(ptr, NULL)`. This is because `nullptr` is
 typed, while `NULL` is not. See the [FAQ](faq.md) for more details.
 
 If you're working with floating point numbers, you may want to use the floating
 point variations of some of these macros in order to avoid problems caused by
 rounding. See [Advanced googletest Topics](advanced.md) for details.
 
 Macros in this section work with both narrow and wide string objects (`string`
 and `wstring`).
 
 **Availability**: Linux, Windows, Mac.
 
 **Historical note**: Before February 2016 `*_EQ` had a convention of calling it
 as `ASSERT_EQ(expected, actual)`, so lots of existing code uses this order. Now
 `*_EQ` treats both parameters in the same way.
 
 ### String Comparison
 
 The assertions in this group compare two **C strings**. If you want to compare
 two `string` objects, use `EXPECT_EQ`, `EXPECT_NE`, and etc instead.
 
 <!-- mdformat off(github rendering does not support multiline tables) -->
 
 | Fatal assertion                | Nonfatal assertion             | Verifies                                                 |
 | --------------------------     | ------------------------------ | -------------------------------------------------------- |
 | `ASSERT_STREQ(str1,str2);`     | `EXPECT_STREQ(str1,str2);`     | the two C strings have the same content   		     |
 | `ASSERT_STRNE(str1,str2);`     | `EXPECT_STRNE(str1,str2);`     | the two C strings have different contents 		     |
 | `ASSERT_STRCASEEQ(str1,str2);` | `EXPECT_STRCASEEQ(str1,str2);` | the two C strings have the same content, ignoring case   |
 | `ASSERT_STRCASENE(str1,str2);` | `EXPECT_STRCASENE(str1,str2);` | the two C strings have different contents, ignoring case |
 
 <!-- mdformat on-->
 
 Note that "CASE" in an assertion name means that case is ignored. A `NULL`
 pointer and an empty string are considered *different*.
 
 `*STREQ*` and `*STRNE*` also accept wide C strings (`wchar_t*`). If a comparison
 of two wide strings fails, their values will be printed as UTF-8 narrow strings.
 
 **Availability**: Linux, Windows, Mac.
 
 **See also**: For more string comparison tricks (substring, prefix, suffix, and
 regular expression matching, for example), see [this](advanced.md) in the
 Advanced googletest Guide.
 
 ## Simple Tests
 
 To create a test:
 
 1.  Use the `TEST()` macro to define and name a test function. These are
     ordinary C++ functions that don't return a value.
 2.  In this function, along with any valid C++ statements you want to include,
     use the various googletest assertions to check values.
 3.  The test's result is determined by the assertions; if any assertion in the
     test fails (either fatally or non-fatally), or if the test crashes, the
     entire test fails. Otherwise, it succeeds.
 
 ```c++
 TEST(TestSuiteName, TestName) {
   ... test body ...
 }
 ```
 
 `TEST()` arguments go from general to specific. The *first* argument is the name
 of the test suite, and the *second* argument is the test's name within the test
 case. Both names must be valid C++ identifiers, and they should not contain
 any underscores (`_`). A test's *full name* consists of its containing test suite and
 its individual name. Tests from different test suites can have the same
 individual name.
 
 For example, let's take a simple integer function:
 
 ```c++
 int Factorial(int n);  // Returns the factorial of n
 ```
 
 A test suite for this function might look like:
 
 ```c++
 // Tests factorial of 0.
 TEST(FactorialTest, HandlesZeroInput) {
   EXPECT_EQ(Factorial(0), 1);
 }
 
 // Tests factorial of positive numbers.
 TEST(FactorialTest, HandlesPositiveInput) {
   EXPECT_EQ(Factorial(1), 1);
   EXPECT_EQ(Factorial(2), 2);
   EXPECT_EQ(Factorial(3), 6);
   EXPECT_EQ(Factorial(8), 40320);
 }
 ```
 
 googletest groups the test results by test suites, so logically related tests
 should be in the same test suite; in other words, the first argument to their
 `TEST()` should be the same. In the above example, we have two tests,
 `HandlesZeroInput` and `HandlesPositiveInput`, that belong to the same test
 suite `FactorialTest`.
 
 When naming your test suites and tests, you should follow the same convention as
 for
 [naming functions and classes](https://google.github.io/styleguide/cppguide.html#Function_Names).
 
 **Availability**: Linux, Windows, Mac.
 
 ## Test Fixtures: Using the Same Data Configuration for Multiple Tests {#same-data-multiple-tests}
 
 If you find yourself writing two or more tests that operate on similar data, you
 can use a *test fixture*. This allows you to reuse the same configuration of
 objects for several different tests.
 
 To create a fixture:
 
 1.  Derive a class from `::testing::Test` . Start its body with `protected:`, as
     we'll want to access fixture members from sub-classes.
 2.  Inside the class, declare any objects you plan to use.
 3.  If necessary, write a default constructor or `SetUp()` function to prepare
     the objects for each test. A common mistake is to spell `SetUp()` as
     **`Setup()`** with a small `u` - Use `override` in C++11 to make sure you
     spelled it correctly.
 4.  If necessary, write a destructor or `TearDown()` function to release any
     resources you allocated in `SetUp()` . To learn when you should use the
     constructor/destructor and when you should use `SetUp()/TearDown()`, read
     the [FAQ](faq.md#CtorVsSetUp).
 5.  If needed, define subroutines for your tests to share.
 
 When using a fixture, use `TEST_F()` instead of `TEST()` as it allows you to
 access objects and subroutines in the test fixture:
 
 ```c++
 TEST_F(TestFixtureName, TestName) {
   ... test body ...
 }
 ```
 
 Like `TEST()`, the first argument is the test suite name, but for `TEST_F()`
 this must be the name of the test fixture class. You've probably guessed: `_F`
 is for fixture.
 
 Unfortunately, the C++ macro system does not allow us to create a single macro
 that can handle both types of tests. Using the wrong macro causes a compiler
 error.
 
 Also, you must first define a test fixture class before using it in a
 `TEST_F()`, or you'll get the compiler error "`virtual outside class
 declaration`".
 
 For each test defined with `TEST_F()`, googletest will create a *fresh* test
 fixture at runtime, immediately initialize it via `SetUp()`, run the test,
 clean up by calling `TearDown()`, and then delete the test fixture. Note that
 different tests in the same test suite have different test fixture objects, and
 googletest always deletes a test fixture before it creates the next one.
 googletest does **not** reuse the same test fixture for multiple tests. Any
 changes one test makes to the fixture do not affect other tests.
 
 As an example, let's write tests for a FIFO queue class named `Queue`, which has
 the following interface:
 
 ```c++
 template <typename E>  // E is the element type.
 class Queue {
  public:
   Queue();
   void Enqueue(const E& element);
   E* Dequeue();  // Returns NULL if the queue is empty.
   size_t size() const;
   ...
 };
 ```
 
 First, define a fixture class. By convention, you should give it the name
 `FooTest` where `Foo` is the class being tested.
 
 ```c++
 class QueueTest : public ::testing::Test {
  protected:
   void SetUp() override {
      q1_.Enqueue(1);
      q2_.Enqueue(2);
      q2_.Enqueue(3);
   }
 
   // void TearDown() override {}
 
   Queue<int> q0_;
   Queue<int> q1_;
   Queue<int> q2_;
 };
 ```
 
 In this case, `TearDown()` is not needed since we don't have to clean up after
 each test, other than what's already done by the destructor.
 
 Now we'll write tests using `TEST_F()` and this fixture.
 
 ```c++
 TEST_F(QueueTest, IsEmptyInitially) {
   EXPECT_EQ(q0_.size(), 0);
 }
 
 TEST_F(QueueTest, DequeueWorks) {
   int* n = q0_.Dequeue();
   EXPECT_EQ(n, nullptr);
 
   n = q1_.Dequeue();
   ASSERT_NE(n, nullptr);
   EXPECT_EQ(*n, 1);
   EXPECT_EQ(q1_.size(), 0);
   delete n;
 
   n = q2_.Dequeue();
   ASSERT_NE(n, nullptr);
   EXPECT_EQ(*n, 2);
   EXPECT_EQ(q2_.size(), 1);
   delete n;
 }
 ```
 
 The above uses both `ASSERT_*` and `EXPECT_*` assertions. The rule of thumb is
 to use `EXPECT_*` when you want the test to continue to reveal more errors after
 the assertion failure, and use `ASSERT_*` when continuing after failure doesn't
 make sense. For example, the second assertion in the `Dequeue` test is
 `ASSERT_NE(nullptr, n)`, as we need to dereference the pointer `n` later, which
 would lead to a segfault when `n` is `NULL`.
 
 When these tests run, the following happens:
 
 1.  googletest constructs a `QueueTest` object (let's call it `t1`).
 2.  `t1.SetUp()` initializes `t1`.
 3.  The first test (`IsEmptyInitially`) runs on `t1`.
 4.  `t1.TearDown()` cleans up after the test finishes.
 5.  `t1` is destructed.
 6.  The above steps are repeated on another `QueueTest` object, this time
     running the `DequeueWorks` test.
 
 **Availability**: Linux, Windows, Mac.
 
 ## Invoking the Tests
 
 `TEST()` and `TEST_F()` implicitly register their tests with googletest. So,
 unlike with many other C++ testing frameworks, you don't have to re-list all
 your defined tests in order to run them.
 
 After defining your tests, you can run them with `RUN_ALL_TESTS()`, which
 returns `0` if all the tests are successful, or `1` otherwise. Note that
 `RUN_ALL_TESTS()` runs *all tests* in your link unit--they can be from
 different test suites, or even different source files.
 
 When invoked, the `RUN_ALL_TESTS()` macro:
 
 *   Saves the state of all googletest flags.
 
 *   Creates a test fixture object for the first test.
 
 *   Initializes it via `SetUp()`.
 
 *   Runs the test on the fixture object.
 
 *   Cleans up the fixture via `TearDown()`.
 
 *   Deletes the fixture.
 
 *   Restores the state of all googletest flags.
 
 *   Repeats the above steps for the next test, until all tests have run.
 
 If a fatal failure happens the subsequent steps will be skipped.
 
 > IMPORTANT: You must **not** ignore the return value of `RUN_ALL_TESTS()`, or
 > you will get a compiler error. The rationale for this design is that the
 > automated testing service determines whether a test has passed based on its
 > exit code, not on its stdout/stderr output; thus your `main()` function must
 > return the value of `RUN_ALL_TESTS()`.
 >
 > Also, you should call `RUN_ALL_TESTS()` only **once**. Calling it more than
 > once conflicts with some advanced googletest features (e.g., thread-safe
 > [death tests](advanced.md#death-tests)) and thus is not supported.
 
 **Availability**: Linux, Windows, Mac.
 
 ## Writing the main() Function
 
 Write your own main() function, which should return the value of
 `RUN_ALL_TESTS()`.
 
 You can start from this boilerplate:
 
 ```c++
 #include "this/package/foo.h"
 #include "gtest/gtest.h"
 
 namespace {
 
 // The fixture for testing class Foo.
 class FooTest : public ::testing::Test {
  protected:
   // You can remove any or all of the following functions if its body
   // is empty.
 
   FooTest() {
      // You can do set-up work for each test here.
   }
 
   ~FooTest() override {
      // You can do clean-up work that doesn't throw exceptions here.
   }
 
   // If the constructor and destructor are not enough for setting up
   // and cleaning up each test, you can define the following methods:
 
   void SetUp() override {
      // Code here will be called immediately after the constructor (right
      // before each test).
   }
 
   void TearDown() override {
      // Code here will be called immediately after each test (right
      // before the destructor).
   }
 
   // Objects declared here can be used by all tests in the test suite for Foo.
 };
 
 // Tests that the Foo::Bar() method does Abc.
 TEST_F(FooTest, MethodBarDoesAbc) {
   const std::string input_filepath = "this/package/testdata/myinputfile.dat";
   const std::string output_filepath = "this/package/testdata/myoutputfile.dat";
   Foo f;
   EXPECT_EQ(f.Bar(input_filepath, output_filepath), 0);
 }
 
 // Tests that Foo does Xyz.
 TEST_F(FooTest, DoesXyz) {
   // Exercises the Xyz feature of Foo.
 }
 
 }  // namespace
 
 int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);
   return RUN_ALL_TESTS();
 }
 ```
 
 The `::testing::InitGoogleTest()` function parses the command line for
 googletest flags, and removes all recognized flags. This allows the user to
 control a test program's behavior via various flags, which we'll cover in
 the [AdvancedGuide](advanced.md). You **must** call this function before calling
 `RUN_ALL_TESTS()`, or the flags won't be properly initialized.
 
 On Windows, `InitGoogleTest()` also works with wide strings, so it can be used
 in programs compiled in `UNICODE` mode as well.
 
 But maybe you think that writing all those main() functions is too much work? We
 agree with you completely, and that's why Google Test provides a basic
 implementation of main(). If it fits your needs, then just link your test with
 gtest\_main library and you are good to go.
 
 NOTE: `ParseGUnitFlags()` is deprecated in favor of `InitGoogleTest()`.
 
 ## Known Limitations
 
 *   Google Test is designed to be thread-safe. The implementation is thread-safe
     on systems where the `pthreads` library is available. It is currently
     _unsafe_ to use Google Test assertions from two threads concurrently on
     other systems (e.g. Windows). In most tests this is not an issue as usually
     the assertions are done in the main thread. If you want to help, you can
     volunteer to implement the necessary synchronization primitives in
     `gtest-port.h` for your platform.