target/linux/ar7/files/include

# Googletest FAQ

<!-- GOOGLETEST_CM0014 DO NOT DELETE -->

## Why should test suite names and test names not contain underscore?

Underscore (`_`) is special, as C++ reserves the following to be used by the
compiler and the standard library:

1.  any identifier that starts with an `_` followed by an upper-case letter, and
2.  any identifier that contains two consecutive underscores (i.e. `__`)
    *anywhere* in its name.

User code is *prohibited* from using such identifiers.

Now let's look at what this means for `TEST` and `TEST_F`.

Currently `TEST(TestSuiteName, TestName)` generates a class named
`TestSuiteName_TestName_Test`. What happens if `TestSuiteName` or `TestName`
contains `_`?

1.  If `TestSuiteName` starts with an `_` followed by an upper-case letter (say,
    `_Foo`), we end up with `_Foo_TestName_Test`, which is reserved and thus
    invalid.
2.  If `TestSuiteName` ends with an `_` (say, `Foo_`), we get
    `Foo__TestName_Test`, which is invalid.
3.  If `TestName` starts with an `_` (say, `_Bar`), we get
    `TestSuiteName__Bar_Test`, which is invalid.
4.  If `TestName` ends with an `_` (say, `Bar_`), we get
    `TestSuiteName_Bar__Test`, which is invalid.

So clearly `TestSuiteName` and `TestName` cannot start or end with `_`
(Actually, `TestSuiteName` can start with `_` -- as long as the `_` isn't
followed by an upper-case letter. But that's getting complicated. So for
simplicity we just say that it cannot start with `_`.).

It may seem fine for `TestSuiteName` and `TestName` to contain `_` in the
middle. However, consider this:

```c++
TEST(Time, Flies_Like_An_Arrow) { ... }
TEST(Time_Flies, Like_An_Arrow) { ... }
```

Now, the two `TEST`s will both generate the same class
(`Time_Flies_Like_An_Arrow_Test`). That's not good.

So for simplicity, we just ask the users to avoid `_` in `TestSuiteName` and
`TestName`. The rule is more constraining than necessary, but it's simple and
easy to remember. It also gives googletest some wiggle room in case its
implementation needs to change in the future.

If you violate the rule, there may not be immediate consequences, but your test
may (just may) break with a new compiler (or a new version of the compiler you
are using) or with a new version of googletest. Therefore it's best to follow
the rule.

## Why does googletest support `EXPECT_EQ(NULL, ptr)` and `ASSERT_EQ(NULL, ptr)` but not `EXPECT_NE(NULL, ptr)` and `ASSERT_NE(NULL, ptr)`?

First of all you can use `EXPECT_NE(nullptr, ptr)` and `ASSERT_NE(nullptr,
ptr)`. This is the preferred syntax in the style guide because nullptr does not
have the type problems that NULL does. Which is why NULL does not work.

Due to some peculiarity of C++, it requires some non-trivial template meta
programming tricks to support using `NULL` as an argument of the `EXPECT_XX()`
and `ASSERT_XX()` macros. Therefore we only do it where it's most needed
(otherwise we make the implementation of googletest harder to maintain and more
error-prone than necessary).

The `EXPECT_EQ()` macro takes the *expected* value as its first argument and the
*actual* value as the second. It's reasonable that someone wants to write
`EXPECT_EQ(NULL, some_expression)`, and this indeed was requested several times.
Therefore we implemented it.

The need for `EXPECT_NE(NULL, ptr)` isn't nearly as strong. When the assertion
fails, you already know that `ptr` must be `NULL`, so it doesn't add any
information to print `ptr` in this case. That means `EXPECT_TRUE(ptr != NULL)`
works just as well.

If we were to support `EXPECT_NE(NULL, ptr)`, for consistency we'll have to
support `EXPECT_NE(ptr, NULL)` as well, as unlike `EXPECT_EQ`, we don't have a
convention on the order of the two arguments for `EXPECT_NE`. This means using
the template meta programming tricks twice in the implementation, making it even
harder to understand and maintain. We believe the benefit doesn't justify the
cost.

Finally, with the growth of the gMock matcher library, we are encouraging people
to use the unified `EXPECT_THAT(value, matcher)` syntax more often in tests. One
significant advantage of the matcher approach is that matchers can be easily
combined to form new matchers, while the `EXPECT_NE`, etc, macros cannot be
easily combined. Therefore we want to invest more in the matchers than in the
`EXPECT_XX()` macros.

## I need to test that different implementations of an interface satisfy some common requirements. Should I use typed tests or value-parameterized tests?

For testing various implementations of the same interface, either typed tests or
value-parameterized tests can get it done. It's really up to you the user to
decide which is more convenient for you, depending on your particular case. Some
rough guidelines:

*   Typed tests can be easier to write if instances of the different
    implementations can be created the same way, modulo the type. For example,
    if all these implementations have a public default constructor (such that
    you can write `new TypeParam`), or if their factory functions have the same
    form (e.g. `CreateInstance<TypeParam>()`).
*   Value-parameterized tests can be easier to write if you need different code
    patterns to create different implementations' instances, e.g. `new Foo` vs
    `new Bar(5)`. To accommodate for the differences, you can write factory
    function wrappers and pass these function pointers to the tests as their
    parameters.
*   When a typed test fails, the default output includes the name of the type,
    which can help you quickly identify which implementation is wrong.
    Value-parameterized tests only show the number of the failed iteration by
    default. You will need to define a function that returns the iteration name
    and pass it as the third parameter to INSTANTIATE_TEST_SUITE_P to have more
    useful output.
*   When using typed tests, you need to make sure you are testing against the
    interface type, not the concrete types (in other words, you want to make
    sure `implicit_cast<MyInterface*>(my_concrete_impl)` works, not just that
    `my_concrete_impl` works). It's less likely to make mistakes in this area
    when using value-parameterized tests.

I hope I didn't confuse you more. :-) If you don't mind, I'd suggest you to give
both approaches a try. Practice is a much better way to grasp the subtle
differences between the two tools. Once you have some concrete experience, you
can much more easily decide which one to use the next time.

## I got some run-time errors about invalid proto descriptors when using `ProtocolMessageEquals`. Help!

**Note:** `ProtocolMessageEquals` and `ProtocolMessageEquiv` are *deprecated*
now. Please use `EqualsProto`, etc instead.

`ProtocolMessageEquals` and `ProtocolMessageEquiv` were redefined recently and
are now less tolerant of invalid protocol buffer definitions. In particular, if
you have a `foo.proto` that doesn't fully qualify the type of a protocol message
it references (e.g. `message<Bar>` where it should be `message<blah.Bar>`), you
will now get run-time errors like:

```
... descriptor.cc:...] Invalid proto descriptor for file "path/to/foo.proto":
... descriptor.cc:...]  blah.MyMessage.my_field: ".Bar" is not defined.
```

If you see this, your `.proto` file is broken and needs to be fixed by making
the types fully qualified. The new definition of `ProtocolMessageEquals` and
`ProtocolMessageEquiv` just happen to reveal your bug.

## My death test modifies some state, but the change seems lost after the death test finishes. Why?

Death tests (`EXPECT_DEATH`, etc) are executed in a sub-process s.t. the
expected crash won't kill the test program (i.e. the parent process). As a
result, any in-memory side effects they incur are observable in their respective
sub-processes, but not in the parent process. You can think of them as running
in a parallel universe, more or less.

In particular, if you use mocking and the death test statement invokes some mock
methods, the parent process will think the calls have never occurred. Therefore,
you may want to move your `EXPECT_CALL` statements inside the `EXPECT_DEATH`
macro.

## EXPECT_EQ(htonl(blah), blah_blah) generates weird compiler errors in opt mode. Is this a googletest bug?

Actually, the bug is in `htonl()`.

According to `'man htonl'`, `htonl()` is a *function*, which means it's valid to
use `htonl` as a function pointer. However, in opt mode `htonl()` is defined as
a *macro*, which breaks this usage.

Worse, the macro definition of `htonl()` uses a `gcc` extension and is *not*
standard C++. That hacky implementation has some ad hoc limitations. In
particular, it prevents you from writing `Foo<sizeof(htonl(x))>()`, where `Foo`
is a template that has an integral argument.

The implementation of `EXPECT_EQ(a, b)` uses `sizeof(... a ...)` inside a
template argument, and thus doesn't compile in opt mode when `a` contains a call
to `htonl()`. It is difficult to make `EXPECT_EQ` bypass the `htonl()` bug, as
the solution must work with different compilers on various platforms.

`htonl()` has some other problems as described in `//util/endian/endian.h`,
which defines `ghtonl()` to replace it. `ghtonl()` does the same thing `htonl()`
does, only without its problems. We suggest you to use `ghtonl()` instead of
`htonl()`, both in your tests and production code.

`//util/endian/endian.h` also defines `ghtons()`, which solves similar problems
in `htons()`.

Don't forget to add `//util/endian` to the list of dependencies in the `BUILD`
file wherever `ghtonl()` and `ghtons()` are used. The library consists of a
single header file and will not bloat your binary.

## The compiler complains about "undefined references" to some static const member variables, but I did define them in the class body. What's wrong?

If your class has a static data member:

```c++
// foo.h
class Foo {
  ...
  static const int kBar = 100;
};
```

You also need to define it *outside* of the class body in `foo.cc`:

```c++
const int Foo::kBar;  // No initializer here.
```

Otherwise your code is **invalid C++**, and may break in unexpected ways. In
particular, using it in googletest comparison assertions (`EXPECT_EQ`, etc) will
generate an "undefined reference" linker error. The fact that "it used to work"
doesn't mean it's valid. It just means that you were lucky. :-)

## Can I derive a test fixture from another?

Yes.

Each test fixture has a corresponding and same named test suite. This means only
one test suite can use a particular fixture. Sometimes, however, multiple test
cases may want to use the same or slightly different fixtures. For example, you
may want to make sure that all of a GUI library's test suites don't leak
important system resources like fonts and brushes.

In googletest, you share a fixture among test suites by putting the shared logic
in a base test fixture, then deriving from that base a separate fixture for each
test suite that wants to use this common logic. You then use `TEST_F()` to write
tests using each derived fixture.

Typically, your code looks like this:

```c++
// Defines a base test fixture.
class BaseTest : public ::testing::Test {
 protected:
  ...
};

// Derives a fixture FooTest from BaseTest.
class FooTest : public BaseTest {
 protected:
  void SetUp() override {
    BaseTest::SetUp();  // Sets up the base fixture first.
    ... additional set-up work ...
  }

  void TearDown() override {
    ... clean-up work for FooTest ...
    BaseTest::TearDown();  // Remember to tear down the base fixture
                           // after cleaning up FooTest!
  }

  ... functions and variables for FooTest ...
};

// Tests that use the fixture FooTest.
TEST_F(FooTest, Bar) { ... }
TEST_F(FooTest, Baz) { ... }

... additional fixtures derived from BaseTest ...
```

If necessary, you can continue to derive test fixtures from a derived fixture.
googletest has no limit on how deep the hierarchy can be.

For a complete example using derived test fixtures, see
[sample5_unittest.cc](../samples/sample5_unittest.cc).

## My compiler complains "void value not ignored as it ought to be." What does this mean?

You're probably using an `ASSERT_*()` in a function that doesn't return `void`.
`ASSERT_*()` can only be used in `void` functions, due to exceptions being
disabled by our build system. Please see more details
[here](advanced.md#assertion-placement).

## My death test hangs (or seg-faults). How do I fix it?

In googletest, death tests are run in a child process and the way they work is
delicate. To write death tests you really need to understand how they work.
Please make sure you have read [this](advanced.md#how-it-works).

In particular, death tests don't like having multiple threads in the parent
process. So the first thing you can try is to eliminate creating threads outside
of `EXPECT_DEATH()`. For example, you may want to use mocks or fake objects
instead of real ones in your tests.

Sometimes this is impossible as some library you must use may be creating
threads before `main()` is even reached. In this case, you can try to minimize
the chance of conflicts by either moving as many activities as possible inside
`EXPECT_DEATH()` (in the extreme case, you want to move everything inside), or
leaving as few things as possible in it. Also, you can try to set the death test
style to `"threadsafe"`, which is safer but slower, and see if it helps.

If you go with thread-safe death tests, remember that they rerun the test
program from the beginning in the child process. Therefore make sure your
program can run side-by-side with itself and is deterministic.

In the end, this boils down to good concurrent programming. You have to make
sure that there is no race conditions or dead locks in your program. No silver
bullet - sorry!

## Should I use the constructor/destructor of the test fixture or SetUp()/TearDown()? {#CtorVsSetUp}

The first thing to remember is that googletest does **not** reuse the same test
fixture object across multiple tests. For each `TEST_F`, googletest will create
a **fresh** test fixture object, immediately call `SetUp()`, run the test body,
call `TearDown()`, and then delete the test fixture object.

When you need to write per-test set-up and tear-down logic, you have the choice
between using the test fixture constructor/destructor or `SetUp()/TearDown()`.
The former is usually preferred, as it has the following benefits:

*   By initializing a member variable in the constructor, we have the option to
    make it `const`, which helps prevent accidental changes to its value and
    makes the tests more obviously correct.
*   In case we need to subclass the test fixture class, the subclass'
    constructor is guaranteed to call the base class' constructor *first*, and
    the subclass' destructor is guaranteed to call the base class' destructor
    *afterward*. With `SetUp()/TearDown()`, a subclass may make the mistake of
Mode	Name	Size
d---------	asm-mips / ar7	30	log stats plain
d---------	linux	35	log stats plain