@permaweb/wasm-metering

Now that you have read [Primer](V1_5_Primer.md) and learned how to write tests using Google Test, it's time to learn some new tricks. This document will show you more assertions as well as how to construct complex failure messages, propagate fatal failures, reuse and speed up your test fixtures, and use various flags with your tests. # More Assertions # This section covers some less frequently used, but still significant, assertions. ## Explicit Success and Failure ## These three assertions do not actually test a value or expression. Instead, they generate a success or failure directly. Like the macros that actually perform a test, you may stream a custom failure message into the them. | `SUCCEED();` | |:-------------| Generates a success. This does NOT make the overall test succeed. A test is considered successful only if none of its assertions fail during its execution. Note: `SUCCEED()` is purely documentary and currently doesn't generate any user-visible output. However, we may add `SUCCEED()` messages to Google Test's output in the future. | `FAIL();` | `ADD_FAILURE();` | |:-----------|:-----------------| `FAIL*` generates a fatal failure while `ADD_FAILURE*` generates a nonfatal failure. These are useful when control flow, rather than a Boolean expression, deteremines the test's success or failure. For example, you might want to write something like: ``` switch(expression) { case 1: ... some checks ... case 2: ... some other checks ... default: FAIL() << "We shouldn't get here."; } ``` _Availability_: Linux, Windows, Mac. ## Exception Assertions ## These are for verifying that a piece of code throws (or does not throw) an exception of the given type: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_THROW(`_statement_, _exception\_type_`);` | `EXPECT_THROW(`_statement_, _exception\_type_`);` | _statement_ throws an exception of the given type | | `ASSERT_ANY_THROW(`_statement_`);` | `EXPECT_ANY_THROW(`_statement_`);` | _statement_ throws an exception of any type | | `ASSERT_NO_THROW(`_statement_`);` | `EXPECT_NO_THROW(`_statement_`);` | _statement_ doesn't throw any exception | Examples: ``` ASSERT_THROW(Foo(5), bar_exception); EXPECT_NO_THROW({ int n = 5; Bar(&n); }); ``` _Availability_: Linux, Windows, Mac; since version 1.1.0. ## Predicate Assertions for Better Error Messages ## Even though Google Test has a rich set of assertions, they can never be complete, as it's impossible (nor a good idea) to anticipate all the scenarios a user might run into. Therefore, sometimes a user has to use `EXPECT_TRUE()` to check a complex expression, for lack of a better macro. This has the problem of not showing you the values of the parts of the expression, making it hard to understand what went wrong. As a workaround, some users choose to construct the failure message by themselves, streaming it into `EXPECT_TRUE()`. However, this is awkward especially when the expression has side-effects or is expensive to evaluate. Google Test gives you three different options to solve this problem: ### Using an Existing Boolean Function ### If you already have a function or a functor that returns `bool` (or a type that can be implicitly converted to `bool`), you can use it in a _predicate assertion_ to get the function arguments printed for free: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_PRED1(`_pred1, val1_`);` | `EXPECT_PRED1(`_pred1, val1_`);` | _pred1(val1)_ returns true | | `ASSERT_PRED2(`_pred2, val1, val2_`);` | `EXPECT_PRED2(`_pred2, val1, val2_`);` | _pred2(val1, val2)_ returns true | | ... | ... | ... | In the above, _predn_ is an _n_-ary predicate function or functor, where _val1_, _val2_, ..., and _valn_ are its arguments. The assertion succeeds if the predicate returns `true` when applied to the given arguments, and fails otherwise. When the assertion fails, it prints the value of each argument. In either case, the arguments are evaluated exactly once. Here's an example. Given ``` // Returns true iff m and n have no common divisors except 1. bool MutuallyPrime(int m, int n) { ... } const int a = 3; const int b = 4; const int c = 10; ``` the assertion `EXPECT_PRED2(MutuallyPrime, a, b);` will succeed, while the assertion `EXPECT_PRED2(MutuallyPrime, b, c);` will fail with the message <pre> !MutuallyPrime(b, c) is false, where b is 4 c is 10 </pre> **Notes:** 1. If you see a compiler error "no matching function to call" when using `ASSERT_PRED*` or `EXPECT_PRED*`, please see [this](V1_5_FAQ.md#the-compiler-complains-about-undefined-references-to-some-static-const-member-variables-but-i-did-define-them-in-the-class-body-whats-wrong) for how to resolve it. 1. Currently we only provide predicate assertions of arity <= 5. If you need a higher-arity assertion, let us know. _Availability_: Linux, Windows, Mac ### Using a Function That Returns an AssertionResult ### While `EXPECT_PRED*()` and friends are handy for a quick job, the syntax is not satisfactory: you have to use different macros for different arities, and it feels more like Lisp than C++. The `::testing::AssertionResult` class solves this problem. An `AssertionResult` object represents the result of an assertion (whether it's a success or a failure, and an associated message). You can create an `AssertionResult` using one of these factory functions: ``` namespace testing { // Returns an AssertionResult object to indicate that an assertion has // succeeded. AssertionResult AssertionSuccess(); // Returns an AssertionResult object to indicate that an assertion has // failed. AssertionResult AssertionFailure(); } ``` You can then use the `<<` operator to stream messages to the `AssertionResult` object. To provide more readable messages in Boolean assertions (e.g. `EXPECT_TRUE()`), write a predicate function that returns `AssertionResult` instead of `bool`. For example, if you define `IsEven()` as: ``` ::testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return ::testing::AssertionSuccess(); else return ::testing::AssertionFailure() << n << " is odd"; } ``` instead of: ``` bool IsEven(int n) { return (n % 2) == 0; } ``` the failed assertion `EXPECT_TRUE(IsEven(Fib(4)))` will print: <pre> Value of: !IsEven(Fib(4)) Actual: false (*3 is odd*) Expected: true </pre> instead of a more opaque <pre> Value of: !IsEven(Fib(4)) Actual: false Expected: true </pre> If you want informative messages in `EXPECT_FALSE` and `ASSERT_FALSE` as well, and are fine with making the predicate slower in the success case, you can supply a success message: ``` ::testing::AssertionResult IsEven(int n) { if ((n % 2) == 0) return ::testing::AssertionSuccess() << n << " is even"; else return ::testing::AssertionFailure() << n << " is odd"; } ``` Then the statement `EXPECT_FALSE(IsEven(Fib(6)))` will print <pre> Value of: !IsEven(Fib(6)) Actual: true (8 is even) Expected: false </pre> _Availability_: Linux, Windows, Mac; since version 1.4.1. ### Using a Predicate-Formatter ### If you find the default message generated by `(ASSERT|EXPECT)_PRED*` and `(ASSERT|EXPECT)_(TRUE|FALSE)` unsatisfactory, or some arguments to your predicate do not support streaming to `ostream`, you can instead use the following _predicate-formatter assertions_ to _fully_ customize how the message is formatted: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_PRED_FORMAT1(`_pred\_format1, val1_`);` | `EXPECT_PRED_FORMAT1(`_pred\_format1, val1_`); | _pred\_format1(val1)_ is successful | | `ASSERT_PRED_FORMAT2(`_pred\_format2, val1, val2_`);` | `EXPECT_PRED_FORMAT2(`_pred\_format2, val1, val2_`);` | _pred\_format2(val1, val2)_ is successful | | `...` | `...` | `...` | The difference between this and the previous two groups of macros is that instead of a predicate, `(ASSERT|EXPECT)_PRED_FORMAT*` take a _predicate-formatter_ (_pred\_formatn_), which is a function or functor with the signature: `::testing::AssertionResult PredicateFormattern(const char* `_expr1_`, const char* `_expr2_`, ... const char* `_exprn_`, T1 `_val1_`, T2 `_val2_`, ... Tn `_valn_`);` where _val1_, _val2_, ..., and _valn_ are the values of the predicate arguments, and _expr1_, _expr2_, ..., and _exprn_ are the corresponding expressions as they appear in the source code. The types `T1`, `T2`, ..., and `Tn` can be either value types or reference types. For example, if an argument has type `Foo`, you can declare it as either `Foo` or `const Foo&`, whichever is appropriate. A predicate-formatter returns a `::testing::AssertionResult` object to indicate whether the assertion has succeeded or not. The only way to create such an object is to call one of these factory functions: As an example, let's improve the failure message in the previous example, which uses `EXPECT_PRED2()`: ``` // Returns the smallest prime common divisor of m and n, // or 1 when m and n are mutually prime. int SmallestPrimeCommonDivisor(int m, int n) { ... } // A predicate-formatter for asserting that two integers are mutually prime. ::testing::AssertionResult AssertMutuallyPrime(const char* m_expr, const char* n_expr, int m, int n) { if (MutuallyPrime(m, n)) return ::testing::AssertionSuccess(); return ::testing::AssertionFailure() << m_expr << " and " << n_expr << " (" << m << " and " << n << ") are not mutually prime, " << "as they have a common divisor " << SmallestPrimeCommonDivisor(m, n); } ``` With this predicate-formatter, we can use ``` EXPECT_PRED_FORMAT2(AssertMutuallyPrime, b, c); ``` to generate the message <pre> b and c (4 and 10) are not mutually prime, as they have a common divisor 2. </pre> As you may have realized, many of the assertions we introduced earlier are special cases of `(EXPECT|ASSERT)_PRED_FORMAT*`. In fact, most of them are indeed defined using `(EXPECT|ASSERT)_PRED_FORMAT*`. _Availability_: Linux, Windows, Mac. ## Floating-Point Comparison ## Comparing floating-point numbers is tricky. Due to round-off errors, it is very unlikely that two floating-points will match exactly. Therefore, `ASSERT_EQ` 's naive comparison usually doesn't work. And since floating-points can have a wide value range, no single fixed error bound works. It's better to compare by a fixed relative error bound, except for values close to 0 due to the loss of precision there. In general, for floating-point comparison to make sense, the user needs to carefully choose the error bound. If they don't want or care to, comparing in terms of Units in the Last Place (ULPs) is a good default, and Google Test provides assertions to do this. Full details about ULPs are quite long; if you want to learn more, see [this article on float comparison](http://www.cygnus-software.com/papers/comparingfloats/comparingfloats.htm). ### Floating-Point Macros ### | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_FLOAT_EQ(`_expected, actual_`);` | `EXPECT_FLOAT_EQ(`_expected, actual_`);` | the two `float` values are almost equal | | `ASSERT_DOUBLE_EQ(`_expected, actual_`);` | `EXPECT_DOUBLE_EQ(`_expected, actual_`);` | the two `double` values are almost equal | By "almost equal", we mean the two values are within 4 ULP's from each other. The following assertions allow you to choose the acceptable error bound: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_NEAR(`_val1, val2, abs\_error_`);` | `EXPECT_NEAR`_(val1, val2, abs\_error_`);` | the difference between _val1_ and _val2_ doesn't exceed the given absolute error | _Availability_: Linux, Windows, Mac. ### Floating-Point Predicate-Format Functions ### Some floating-point operations are useful, but not that often used. In order to avoid an explosion of new macros, we provide them as predicate-format functions that can be used in predicate assertion macros (e.g. `EXPECT_PRED_FORMAT2`, etc). ``` EXPECT_PRED_FORMAT2(::testing::FloatLE, val1, val2); EXPECT_PRED_FORMAT2(::testing::DoubleLE, val1, val2); ``` Verifies that _val1_ is less than, or almost equal to, _val2_. You can replace `EXPECT_PRED_FORMAT2` in the above table with `ASSERT_PRED_FORMAT2`. _Availability_: Linux, Windows, Mac. ## Windows HRESULT assertions ## These assertions test for `HRESULT` success or failure. | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_HRESULT_SUCCEEDED(`_expression_`);` | `EXPECT_HRESULT_SUCCEEDED(`_expression_`);` | _expression_ is a success `HRESULT` | | `ASSERT_HRESULT_FAILED(`_expression_`);` | `EXPECT_HRESULT_FAILED(`_expression_`);` | _expression_ is a failure `HRESULT` | The generated output contains the human-readable error message associated with the `HRESULT` code returned by _expression_. You might use them like this: ``` CComPtr shell; ASSERT_HRESULT_SUCCEEDED(shell.CoCreateInstance(L"Shell.Application")); CComVariant empty; ASSERT_HRESULT_SUCCEEDED(shell->ShellExecute(CComBSTR(url), empty, empty, empty, empty)); ``` _Availability_: Windows. ## Type Assertions ## You can call the function ``` ::testing::StaticAssertTypeEq<T1, T2>(); ``` to assert that types `T1` and `T2` are the same. The function does nothing if the assertion is satisfied. If the types are different, the function call will fail to compile, and the compiler error message will likely (depending on the compiler) show you the actual values of `T1` and `T2`. This is mainly useful inside template code. _Caveat:_ When used inside a member function of a class template or a function template, `StaticAssertTypeEq<T1, T2>()` is effective _only if_ the function is instantiated. For example, given: ``` template <typename T> class Foo { public: void Bar() { ::testing::StaticAssertTypeEq<int, T>(); } }; ``` the code: ``` void Test1() { Foo<bool> foo; } ``` will _not_ generate a compiler error, as `Foo<bool>::Bar()` is never actually instantiated. Instead, you need: ``` void Test2() { Foo<bool> foo; foo.Bar(); } ``` to cause a compiler error. _Availability:_ Linux, Windows, Mac; since version 1.3.0. ## Assertion Placement ## You can use assertions in any C++ function. In particular, it doesn't have to be a method of the test fixture class. The one constraint is that assertions that generate a fatal failure (`FAIL*` and `ASSERT_*`) can only be used in void-returning functions. This is a consequence of Google Test not using exceptions. By placing it in a non-void function you'll get a confusing compile error like `"error: void value not ignored as it ought to be"`. If you need to use assertions in a function that returns non-void, one option is to make the function return the value in an out parameter instead. For example, you can rewrite `T2 Foo(T1 x)` to `void Foo(T1 x, T2* result)`. You need to make sure that `*result` contains some sensible value even when the function returns prematurely. As the function now returns `void`, you can use any assertion inside of it. If changing the function's type is not an option, you should just use assertions that generate non-fatal failures, such as `ADD_FAILURE*` and `EXPECT_*`. _Note_: Constructors and destructors are not considered void-returning functions, according to the C++ language specification, and so you may not use fatal assertions in them. You'll get a compilation error if you try. A simple workaround is to transfer the entire body of the constructor or destructor to a private void-returning method. However, you should be aware that a fatal assertion failure in a constructor does not terminate the current test, as your intuition might suggest; it merely returns from the constructor early, possibly leaving your object in a partially-constructed state. Likewise, a fatal assertion failure in a destructor may leave your object in a partially-destructed state. Use assertions carefully in these situations! # Death Tests # In many applications, there are assertions that can cause application failure if a condition is not met. These sanity checks, which ensure that the program is in a known good state, are there to fail at the earliest possible time after some program state is corrupted. If the assertion checks the wrong condition, then the program may proceed in an erroneous state, which could lead to memory corruption, security holes, or worse. Hence it is vitally important to test that such assertion statements work as expected. Since these precondition checks cause the processes to die, we call such tests _death tests_. More generally, any test that checks that a program terminates in an expected fashion is also a death test. If you want to test `EXPECT_*()/ASSERT_*()` failures in your test code, see [Catching Failures](#catching-failures). ## How to Write a Death Test ## Google Test has the following macros to support death tests: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_DEATH(`_statement, regex_`); | `EXPECT_DEATH(`_statement, regex_`); | _statement_ crashes with the given error | | `ASSERT_DEATH_IF_SUPPORTED(`_statement, regex_`); | `EXPECT_DEATH_IF_SUPPORTED(`_statement, regex_`); | if death tests are supported, verifies that _statement_ crashes with the given error; otherwise verifies nothing | | `ASSERT_EXIT(`_statement, predicate, regex_`); | `EXPECT_EXIT(`_statement, predicate, regex_`); |_statement_ exits with the given error and its exit code matches _predicate_ | where _statement_ is a statement that is expected to cause the process to die, _predicate_ is a function or function object that evaluates an integer exit status, and _regex_ is a regular expression that the stderr output of _statement_ is expected to match. Note that _statement_ can be _any valid statement_ (including _compound statement_) and doesn't have to be an expression. As usual, the `ASSERT` variants abort the current test function, while the `EXPECT` variants do not. **Note:** We use the word "crash" here to mean that the process terminates with a _non-zero_ exit status code. There are two possibilities: either the process has called `exit()` or `_exit()` with a non-zero value, or it may be killed by a signal. This means that if _statement_ terminates the process with a 0 exit code, it is _not_ considered a crash by `EXPECT_DEATH`. Use `EXPECT_EXIT` instead if this is the case, or if you want to restrict the exit code more precisely. A predicate here must accept an `int` and return a `bool`. The death test succeeds only if the predicate returns `true`. Google Test defines a few predicates that handle the most common cases: ``` ::testing::ExitedWithCode(exit_code) ``` This expression is `true` if the program exited normally with the given exit code. ``` ::testing::KilledBySignal(signal_number) // Not available on Windows. ``` This expression is `true` if the program was killed by the given signal. The `*_DEATH` macros are convenient wrappers for `*_EXIT` that use a predicate that verifies the process' exit code is non-zero. Note that a death test only cares about three things: 1. does _statement_ abort or exit the process? 1. (in the case of `ASSERT_EXIT` and `EXPECT_EXIT`) does the exit status satisfy _predicate_? Or (in the case of `ASSERT_DEATH` and `EXPECT_DEATH`) is the exit status non-zero? And 1. does the stderr output match _regex_? In particular, if _statement_ generates an `ASSERT_*` or `EXPECT_*` failure, it will **not** cause the death test to fail, as Google Test assertions don't abort the process. To write a death test, simply use one of the above macros inside your test function. For example, ``` TEST(My*DeathTest*, Foo) { // This death test uses a compound statement. ASSERT_DEATH({ int n = 5; Foo(&n); }, "Error on line .* of Foo()"); } TEST(MyDeathTest, NormalExit) { EXPECT_EXIT(NormalExit(), ::testing::ExitedWithCode(0), "Success"); } TEST(MyDeathTest, KillMyself) { EXPECT_EXIT(KillMyself(), ::testing::KilledBySignal(SIGKILL), "Sending myself unblockable signal"); } ``` verifies that: * calling `Foo(5)` causes the process to die with the given error message, * calling `NormalExit()` causes the process to print `"Success"` to stderr and exit with exit code 0, and * calling `KillMyself()` kills the process with signal `SIGKILL`. The test function body may contain other assertions and statements as well, if necessary. _Important:_ We strongly recommend you to follow the convention of naming your test case (not test) `*DeathTest` when it contains a death test, as demonstrated in the above example. The `Death Tests And Threads` section below explains why. If a test fixture class is shared by normal tests and death tests, you can use typedef to introduce an alias for the fixture class and avoid duplicating its code: ``` class FooTest : public ::testing::Test { ... }; typedef FooTest FooDeathTest; TEST_F(FooTest, DoesThis) { // normal test } TEST_F(FooDeathTest, DoesThat) { // death test } ``` _Availability:_ Linux, Windows (requires MSVC 8.0 or above), Cygwin, and Mac (the latter three are supported since v1.3.0). `(ASSERT|EXPECT)_DEATH_IF_SUPPORTED` are new in v1.4.0. ## Regular Expression Syntax ## On POSIX systems (e.g. Linux, Cygwin, and Mac), Google Test uses the [POSIX extended regular expression](http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap09.html#tag_09_04) syntax in death tests. To learn about this syntax, you may want to read this [Wikipedia entry](http://en.wikipedia.org/wiki/Regular_expression#POSIX_Extended_Regular_Expressions). On Windows, Google Test uses its own simple regular expression implementation. It lacks many features you can find in POSIX extended regular expressions. For example, we don't support union (`"x|y"`), grouping (`"(xy)"`), brackets (`"[xy]"`), and repetition count (`"x{5,7}"`), among others. Below is what we do support (`A` denotes a literal character, period (`.`), or a single `\\` escape sequence; `x` and `y` denote regular expressions.): | `c` | matches any literal character `c` | |:----|:----------------------------------| | `\\d` | matches any decimal digit | | `\\D` | matches any character that's not a decimal digit | | `\\f` | matches `\f` | | `\\n` | matches `\n` | | `\\r` | matches `\r` | | `\\s` | matches any ASCII whitespace, including `\n` | | `\\S` | matches any character that's not a whitespace | | `\\t` | matches `\t` | | `\\v` | matches `\v` | | `\\w` | matches any letter, `_`, or decimal digit | | `\\W` | matches any character that `\\w` doesn't match | | `\\c` | matches any literal character `c`, which must be a punctuation | | `.` | matches any single character except `\n` | | `A?` | matches 0 or 1 occurrences of `A` | | `A*` | matches 0 or many occurrences of `A` | | `A+` | matches 1 or many occurrences of `A` | | `^` | matches the beginning of a string (not that of each line) | | `$` | matches the end of a string (not that of each line) | | `xy` | matches `x` followed by `y` | To help you determine which capability is available on your system, Google Test defines macro `GTEST_USES_POSIX_RE=1` when it uses POSIX extended regular expressions, or `GTEST_USES_SIMPLE_RE=1` when it uses the simple version. If you want your death tests to work in both cases, you can either `#if` on these macros or use the more limited syntax only. ## How It Works ## Under the hood, `ASSERT_EXIT()` spawns a new process and executes the death test statement in that process. The details of of how precisely that happens depend on the platform and the variable `::testing::GTEST_FLAG(death_test_style)` (which is initialized from the command-line flag `--gtest_death_test_style`). * On POSIX systems, `fork()` (or `clone()` on Linux) is used to spawn the child, after which: * If the variable's value is `"fast"`, the death test statement is immediately executed. * If the variable's value is `"threadsafe"`, the child process re-executes the unit test binary just as it was originally invoked, but with some extra flags to cause just the single death test under consideration to be run. * On Windows, the child is spawned using the `CreateProcess()` API, and re-executes the binary to cause just the single death test under consideration to be run - much like the `threadsafe` mode on POSIX. Other values for the variable are illegal and will cause the death test to fail. Currently, the flag's default value is `"fast"`. However, we reserve the right to change it in the future. Therefore, your tests should not depend on this. In either case, the parent process waits for the child process to complete, and checks that 1. the child's exit status satisfies the predicate, and 1. the child's stderr matches the regular expression. If the death test statement runs to completion without dying, the child process will nonetheless terminate, and the assertion fails. ## Death Tests And Threads ## The reason for the two death test styles has to do with thread safety. Due to well-known problems with forking in the presence of threads, death tests should be run in a single-threaded context. Sometimes, however, it isn't feasible to arrange that kind of environment. For example, statically-initialized modules may start threads before main is ever reached. Once threads have been created, it may be difficult or impossible to clean them up. Google Test has three features intended to raise awareness of threading issues. 1. A warning is emitted if multiple threads are running when a death test is encountered. 1. Test cases with a name ending in "DeathTest" are run before all other tests. 1. It uses `clone()` instead of `fork()` to spawn the child process on Linux (`clone()` is not available on Cygwin and Mac), as `fork()` is more likely to cause the child to hang when the parent process has multiple threads. It's perfectly fine to create threads inside a death test statement; they are executed in a separate process and cannot affect the parent. ## Death Test Styles ## The "threadsafe" death test style was introduced in order to help mitigate the risks of testing in a possibly multithreaded environment. It trades increased test execution time (potentially dramatically so) for improved thread safety. We suggest using the faster, default "fast" style unless your test has specific problems with it. You can choose a particular style of death tests by setting the flag programmatically: ``` ::testing::FLAGS_gtest_death_test_style = "threadsafe"; ``` You can do this in `main()` to set the style for all death tests in the binary, or in individual tests. Recall that flags are saved before running each test and restored afterwards, so you need not do that yourself. For example: ``` TEST(MyDeathTest, TestOne) { ::testing::FLAGS_gtest_death_test_style = "threadsafe"; // This test is run in the "threadsafe" style: ASSERT_DEATH(ThisShouldDie(), ""); } TEST(MyDeathTest, TestTwo) { // This test is run in the "fast" style: ASSERT_DEATH(ThisShouldDie(), ""); } int main(int argc, char** argv) { ::testing::InitGoogleTest(&argc, argv); ::testing::FLAGS_gtest_death_test_style = "fast"; return RUN_ALL_TESTS(); } ``` ## Caveats ## The _statement_ argument of `ASSERT_EXIT()` can be any valid C++ statement except that it can not return from the current function. This means _statement_ should not contain `return` or a macro that might return (e.g. `ASSERT_TRUE()` ). If _statement_ returns before it crashes, Google Test will print an error message, and the test will fail. Since _statement_ runs in the child process, any in-memory side effect (e.g. modifying a variable, releasing memory, etc) it causes will _not_ be observable in the parent process. In particular, if you release memory in a death test, your program will fail the heap check as the parent process will never see the memory reclaimed. To solve this problem, you can 1. try not to free memory in a death test; 1. free the memory again in the parent process; or 1. do not use the heap checker in your program. Due to an implementation detail, you cannot place multiple death test assertions on the same line; otherwise, compilation will fail with an unobvious error message. Despite the improved thread safety afforded by the "threadsafe" style of death test, thread problems such as deadlock are still possible in the presence of handlers registered with `pthread_atfork(3)`. # Using Assertions in Sub-routines # ## Adding Traces to Assertions ## If a test sub-routine is called from several places, when an assertion inside it fails, it can be hard to tell which invocation of the sub-routine the failure is from. You can alleviate this problem using extra logging or custom failure messages, but that usually clutters up your tests. A better solution is to use the `SCOPED_TRACE` macro: | `SCOPED_TRACE(`_message_`);` | |:-----------------------------| where _message_ can be anything streamable to `std::ostream`. This macro will cause the current file name, line number, and the given message to be added in every failure message. The effect will be undone when the control leaves the current lexical scope. For example, ``` 10: void Sub1(int n) { 11: EXPECT_EQ(1, Bar(n)); 12: EXPECT_EQ(2, Bar(n + 1)); 13: } 14: 15: TEST(FooTest, Bar) { 16: { 17: SCOPED_TRACE("A"); // This trace point will be included in 18: // every failure in this scope. 19: Sub1(1); 20: } 21: // Now it won't. 22: Sub1(9); 23: } ``` could result in messages like these: ``` path/to/foo_test.cc:11: Failure Value of: Bar(n) Expected: 1 Actual: 2 Trace: path/to/foo_test.cc:17: A path/to/foo_test.cc:12: Failure Value of: Bar(n + 1) Expected: 2 Actual: 3 ``` Without the trace, it would've been difficult to know which invocation of `Sub1()` the two failures come from respectively. (You could add an extra message to each assertion in `Sub1()` to indicate the value of `n`, but that's tedious.) Some tips on using `SCOPED_TRACE`: 1. With a suitable message, it's often enough to use `SCOPED_TRACE` at the beginning of a sub-routine, instead of at each call site. 1. When calling sub-routines inside a loop, make the loop iterator part of the message in `SCOPED_TRACE` such that you can know which iteration the failure is from. 1. Sometimes the line number of the trace point is enough for identifying the particular invocation of a sub-routine. In this case, you don't have to choose a unique message for `SCOPED_TRACE`. You can simply use `""`. 1. You can use `SCOPED_TRACE` in an inner scope when there is one in the outer scope. In this case, all active trace points will be included in the failure messages, in reverse order they are encountered. 1. The trace dump is clickable in Emacs' compilation buffer - hit return on a line number and you'll be taken to that line in the source file! _Availability:_ Linux, Windows, Mac. ## Propagating Fatal Failures ## A common pitfall when using `ASSERT_*` and `FAIL*` is not understanding that when they fail they only abort the _current function_, not the entire test. For example, the following test will segfault: ``` void Subroutine() { // Generates a fatal failure and aborts the current function. ASSERT_EQ(1, 2); // The following won't be executed. ... } TEST(FooTest, Bar) { Subroutine(); // The intended behavior is for the fatal failure // in Subroutine() to abort the entire test. // The actual behavior: the function goes on after Subroutine() returns. int* p = NULL; *p = 3; // Segfault! } ``` Since we don't use exceptions, it is technically impossible to implement the intended behavior here. To alleviate this, Google Test provides two solutions. You could use either the `(ASSERT|EXPECT)_NO_FATAL_FAILURE` assertions or the `HasFatalFailure()` function. They are described in the following two subsections. ### Asserting on Subroutines ### As shown above, if your test calls a subroutine that has an `ASSERT_*` failure in it, the test will continue after the subroutine returns. This may not be what you want. Often people want fatal failures to propagate like exceptions. For that Google Test offers the following macros: | **Fatal assertion** | **Nonfatal assertion** | **Verifies** | |:--------------------|:-----------------------|:-------------| | `ASSERT_NO_FATAL_FAILURE(`_statement_`);` | `EXPECT_NO_FATAL_FAILURE(`_statement_`);` | _statement_ doesn't generate any new fatal failures in the current thread. | Only failures in the thread that executes the assertion are checked to determine the result of this type of assertions. If _statement_ creates new threads, failures in these threads are ignored. Examples: ``` ASSERT_NO_FATAL_FAILURE(Foo()); int i; EXPECT_NO_FATAL_FAILURE({ i = Bar(); }); ``` _Availability:_ Linux, Windows, Mac. Assertions from multiple threads are currently not supported. ### Checking for Failures in the Current Test ### `HasFatalFailure()` in the `::testing::Test` class returns `true` if an assertion in the current test has suffered a fatal failure. This allows functions to catch fatal failures in a sub-routine and return early. ``` class Test { public: ... static bool HasFatalFailure(); }; ``` The typical usage, which basically simulates the behavior of a thrown exception, is: ``` TEST(FooTest, Bar) { Subroutine(); // Aborts if Subroutine() had a fatal failure. if (HasFatalFailure()) return; // The following won't be executed. ... } ``` If `HasFatalFailure()` is used outside of `TEST()` , `TEST_F()` , or a test fixture, you must add the `::testing::Test::` prefix, as in: ``` if (::testing::Test::HasFatalFailure()) return; ``` Similarly, `HasNonfatalFailure()` returns `true` if the current test has at least one non-fatal failure, and `HasFailure()` returns `true` if the current test has at least one failure of either kind. _Availability:_ Linux, Windows, Mac. `HasNonfatalFailure()` and `HasFailure()` are available since version 1.4.0. # Logging Additional Information # In your test code, you can call `RecordProperty("key", value)` to log additional information, where `value` can be either a C string or a 32-bit integer. The _last_ value recorded for a key will be emitted to the XML output if you specify one. For example, the test ``` TEST_F(WidgetUsageTest, MinAndMaxWidgets) { RecordProperty("MaximumWidgets", ComputeMaxUsage()); RecordProperty("MinimumWidgets", ComputeMinUsage()); } ``` will output XML like this: ``` ... <testcase name="MinAndMaxWidgets" status="run" time="6" classname="WidgetUsageTest" MaximumWidgets="12" MinimumWidgets="9" /> ... ``` _Note_: * `RecordProperty()` is a static member of the `Test` class. Therefore it needs to be prefixed with `::testing::Test::` if used outside of the `TEST` body and the test fixture class. * `key` must be a valid XML attribute name, and cannot conflict with the ones already used by Google Test (`name`, `status`, `time`, and `classname`). _Availability_: Linux, Windows, Mac. # Sharing Resources Between Tests in the Same Test Case # Google Test creates a new test fixture object for each test in order to make tests independent and easier to debug. However, sometimes tests use resources that are expensive to set up, making the one-copy-per-test model prohibitively expensive. If the tests don't change the resource, there's no harm in them sharing a single resource copy. So, in addition to per-test set-up/tear-down, Google Test also supports per-test-case set-up/tear-down. To use it: 1. In your test fixture class (say `FooTest` ), define as `static` some member variables to hold the shared resources. 1. In the same test fixture class, define a `static void SetUpTestCase()` function (remember not to spell it as **`SetupTestCase`** with a small `u`!) to set up the shared resources and a `static void TearDownTestCase()` function to tear them down. That's it! Google Test automatically calls `SetUpTestCase()` before running the _first test_ in the `FooTest` test case (i.e. before creating the first `FooTest` object), and calls `TearDownTestCase()` after running the _last test_ in it (i.e. after deleting the last `FooTest` object). In between, the tests can use the shared resources. Remember that the test order is undefined, so your code can't depend on a test preceding or following another. Also, the tests must either not modify the state of any shared resource, or, if they do modify the state, they must restore the state to its original value before passing control to the next test. Here's an example of per-test-case set-up and tear-down: ``` class FooTest : public ::testing::Test { protected: // Per-test-case set-up. // Called before the first test in this test case. // Can be omitted if not needed. static void SetUpTestCase() { shared_resource_ = new ...; } // Per-test-case tear-down. // Called after the last test in this test case. // Can be omitted if not needed. static void TearDownTestCase() { delete shared_resource_; shared_resource_ = NULL; } // You can define per-test set-up and tear-down logic as usual. virtual void SetUp() { ... } virtual void TearDown() { ... } // Some expensive resource shared by all tests. static T* shared_resource_; }; T* FooTest::shared_resource_ = NULL; TEST_F(FooTest, Test1) { ... you can refer to shared_resource here ... } TEST_F(FooTest, Test2) { ... you can refer to shared_resource here ... } ``` _Availability:_ Linux, Windows, Mac. # Global Set-Up and Tear-Down # Just as you can do set-up and tear-down at the test level and the test case level, you can also do it at the test program level. Here's how. First, you subclass the `::testing::Environment` class to define a test environment, which knows how to set-up and tear-down: ``` class Environment { public: virtual ~Environment() {} // Override this to define how to set up the environment. virtual void SetUp() {} // Override this to define how to tear down the environment. virtual void TearDown() {} }; ``` Then, you register an instance of your environment class with Google Test by calling the `::testing::AddGlobalTestEnvironment()` function: ``` Environment* AddGlobalTestEnvironment(Environment* env); ``` Now, when `RUN_ALL_TESTS()` is called, it first calls the `SetUp()` method of the environment object, then runs the tests if there was no fatal failures, and finally calls `TearDown()` of the environment object. It's OK to register multiple environment objects. In this case, their `SetUp()` will be called in the order they are registered, and their `TearDown()` will be called in the reverse order. Note that Google Test takes ownership of the registered environment objects. Therefore **do not delete them** by yourself. You should call `AddGlobalTestEnvironment()` before `RUN_ALL_TESTS()` is called, probably in `main()`. If you use `gtest_main`, you need to call this before `main()` starts for it to take effect. One way to do this is to define a global variable like this: ``` ::testing::Environment* const foo_env = ::testing::AddGlobalTestEnvironment(new FooEnvironment); ``` However, we strongly recommend you to write your own `main()` and call `AddGlobalTestEnvironment()` there, as relying on initialization of global variables makes the code harder to read and may cause problems when you register multiple environments from different translation units and the environments have dependencies among them (remember that the compiler doesn't guarantee the order in which global variables from different translation units are initialized). _Availability:_ Linux, Windows, Mac. # Value Parameterized Tests # _Value-parameterized tests_ allow you to test your code with different parameters without writing multiple copies of the same test. Suppose you write a test for your code and then realize that your code is affected by a presence of a Boolean command line flag. ``` TEST(MyCodeTest, TestFoo) { // A code to test foo(). } ``` Usually people factor their test code into a function with a Boolean parameter in such situations. The function sets the flag, then executes the testing code. ``` void TestFooHelper(bool flag_value) { flag = flag_value; // A code to test foo(). } TEST(MyCodeTest, TestFooo) { TestFooHelper(false); TestFooHelper(true); } ``` But this setup has serious drawbacks. First, when a test assertion fails in your tests, it becomes unclear what value of the parameter caused it to fail. You can stream a clarifying message into your `EXPECT`/`ASSERT` statements, but it you'll have to do it with all of them. Second, you have to add one such helper function per test. What if you have ten tests? Twenty? A hundred? Value-parameterized tests will let you write your test only once and then easily instantiate and run it with an arbitrary number of parameter values. Here are some other situations when value-parameterized tests come handy: * You wan to test different implementations of an OO interface. * You want to test your code over various inputs (a.k.a. data-driven testing). This feature is easy to abuse, so please exercise your good sense when doing it! ## How to Write Value-Parameterized Tests ## To write value-parameterized tests, first you should define a fixture class. It must be derived from `::testing::TestWithParam<T>`, where `T` is the type of your parameter values. `TestWithParam<T>` is itself derived from `::testing::Test`. `T` can be any copyable type. If it's a raw pointer, you are responsible for managing the lifespan of the pointed values. ``` class FooTest : public ::testing::TestWithParam<const char*> { // You can implement all the usual fixture class members here. // To access the test parameter, call GetParam() from class // TestWithParam<T>. }; ``` Then, use the `TEST_P` macro to define as many test patterns using this fixture as you want. The `_P` suffix is for "parameterized" or "pattern", whichever you prefer to think. ``` TEST_P(FooTest, DoesBlah) { // Inside a test, access the test parameter with the GetParam() method // of the TestWithParam<T> class: EXPECT_TRUE(foo.Blah(GetParam())); ... } TEST_P(FooTest, HasBlahBlah) { ... } ``` Finally, you can use `INSTANTIATE_TEST_CASE_P` to instantiate the test case with any set of parameters you want. Google Test defines a number of functions for generating test parameters. They return what we call (surprise!) _parameter generators_. Here is a summary of them, which are all in the `testing` namespace: | `Range(begin, end[, step])` | Yields values `{begin, begin+step, begin+step+step, ...}`. The values do not include `end`. `step` defaults to 1. | |:----------------------------|:------------------------------------------------------------------------------------------------------------------| | `Values(v1, v2, ..., vN)` | Yields values `{v1, v2, ..., vN}`. | | `ValuesIn(container)` and `ValuesIn(begin, end)` | Yields values from a C-style array, an STL-style container, or an iterator range `[begin, end)`. | | `Bool()` | Yields sequence `{false, true}`. | | `Combine(g1, g2, ..., gN)` | Yields all combinations (the Cartesian product for the math savvy) of the values generated by the `N` generators. This is only available if your system provides the `<tr1/tuple>` header. If you are sure your system does, and Google Test disagrees, you can override it by defining `GTEST_HAS_TR1_TUPLE=1`. See comments in [include/gtest/internal/gtest-port.h](../include/gtest/internal/gtest-port.h) for more information. | For more details, see the comments at the definitions of these functions in the [source code](../include/gtest/gtest-param-test.h). The following statement will instantiate tests from the `FooTest` test case each with parameter values `"meeny"`, `"miny"`, and `"moe"`. ``` INSTANTIATE_TEST_CASE_P(InstantiationName, FooTest, ::testing::Values("meeny", "miny", "moe")); ``` To distinguish different instances of the pattern (yes, you can instantiate it more than once), the first argument to `INSTANTIATE_TEST_CASE_P` is a prefix that will be added to the actual test case name. Remember to pick unique prefixes for different instantiations. The tests from the instantiation above will have these names: * `InstantiationName/FooTest.DoesBlah/0` for `"meeny"` * `InstantiationName/FooTest.DoesBlah/1` for `"miny"` * `InstantiationName/FooTest.DoesBlah/2` for `"moe"` * `InstantiationName/FooTest.HasBlahBlah/0` for `"meeny"` * `InstantiationName/FooTest.HasBlahBlah/1` for `"miny"` * `InstantiationName/FooTest.HasBlahBlah/2` for `"moe"` You can use these names in [--gtest\-filter](#running-a-subset-of-the-tests). This statement will instantiate all tests from `FooTest` again, each with parameter values `"cat"` and `"dog"`: ``` const char* pets[] = {"cat", "dog"}; INSTANTIATE_TEST_CASE_P(AnotherInstantiationName, FooTest, ::testing::ValuesIn(pets)); ``` The tests from the instantiation above will have these names: * `AnotherInstantiationName/FooTest.DoesBlah/0` for `"cat"` * `AnotherInstantiationName/FooTest.DoesBlah/1` for `"dog"` * `AnotherInstantiationName/FooTest.HasBlahBlah/0` for `"cat"` * `AnotherInstantiationName/FooTest.HasBlahBlah/1` for `"dog"` Please note that `INSTANTIATE_TEST_CASE_P` will instantiate _all_ tests in the given test case, whether their definitions come before or _after_ the `INSTANTIATE_TEST_CASE_P` statement. You can see [these](../samples/sample7_unittest.cc) [files](../samples/sample8_unittest.cc) for more examples. _Availability_: Linux, Windows (requires MSVC 8.0 or above), Mac; since version 1.2.0. ## Creating Value-Parameterized Abstract Tests ## In the above, we define and instantiate `FooTest` in the same source file. Sometimes you may want to define value-parameterized tests in a library and let other people instantiate them later. This pattern is known as abstract tests. As an example of its application, when you are designing an interface you can write a standard suite of abstract tests (perhaps using a factory function as the test parameter) that all implementations of the interface are expected to pass. When someone implements the interface, he can instantiate your suite to get all the interface-conformance tests for free. To define abstract tests, you should organize your code like this: 1. Put the definition of the parameterized test fixture class (e.g. `FooTest`) in a header file, say `foo_param_test.h`. Think of this as _declaring_ your abstract tests. 1. Put the `TEST_P` definitions in `foo_param_test.cc`, which includes `foo_param_test.h`. Think of this as _implementing_ your abstract tests. Once they are defined, you can instantiate them by including `foo_param_test.h`, invoking `INSTANTIATE_TEST_CASE_P()`, and linking with `foo_param_test.cc`. You can instantiate the same abstract test case multiple times, possibly in different source files. # Typed Tests # Suppose you have multiple implementations of the same interface and want to make sure that all of them satisfy some common requirements. Or, you may have defined several types that are supposed to conform to the same "concept" and you want to verify it. In both cases, you want the same test logic repeated for different types. While you can write one `TEST` or `TEST_F` for each type you want to test (and you may even factor the test logic into a function template that you invoke from the `TEST`), it's tedious and doesn't scale: if you want _m_ tests over _n_ types, you'll end up writing _m\*n_ `TEST`s. _Typed tests_ allow you to repeat the same test logic over a list of types. You only need to write the test logic once, although you must know the type list when writing typed tests. Here's how you do it: First, define a fixture class template. It should be parameterized by a type. Remember to derive it from `::testing::Test`: ``` template <typename T> class FooTest : public ::testing::Test { public: ... typedef std::list<T> List; static T shared_; T value_; }; ``` Next, associate a list of types with the test case, which will be repeated for each type in the list: ``` typedef ::testing::Types<char, int, unsigned int> MyTypes; TYPED_TEST_CASE(FooTest, MyTypes); ``` The `typedef` is necessary for the `TYPED_TEST_CASE` macro to parse correctly. Otherwise the compiler will think that each comma in the type list introduces a new macro argument. Then, use `TYPED_TEST()` instead of `TEST_F()` to define a typed test for this test case. You can repeat this as many times as you want: ``` TYPED_TEST(FooTest, DoesBlah) { // Inside a test, refer to the special name TypeParam to get the type // parameter. Since w