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+# gMock for Dummies {#GMockForDummies}
+
+<!-- GOOGLETEST_CM0013 DO NOT DELETE -->
+
+<!-- GOOGLETEST_CM0035 DO NOT DELETE -->
+
+## What Is gMock?
+
+When you write a prototype or test, often it's not feasible or wise to rely on
+real objects entirely. A **mock object** implements the same interface as a real
+object (so it can be used as one), but lets you specify at run time how it will
+be used and what it should do (which methods will be called? in which order? how
+many times? with what arguments? what will they return? etc).
+
+**Note:** It is easy to confuse the term *fake objects* with mock objects. Fakes
+and mocks actually mean very different things in the Test-Driven Development
+(TDD) community:
+
+*   **Fake** objects have working implementations, but usually take some
+    shortcut (perhaps to make the operations less expensive), which makes them
+    not suitable for production. An in-memory file system would be an example of
+    a fake.
+*   **Mocks** are objects pre-programmed with *expectations*, which form a
+    specification of the calls they are expected to receive.
+
+If all this seems too abstract for you, don't worry - the most important thing
+to remember is that a mock allows you to check the *interaction* between itself
+and code that uses it. The difference between fakes and mocks shall become much
+clearer once you start to use mocks.
+
+**gMock** is a library (sometimes we also call it a "framework" to make it sound
+cool) for creating mock classes and using them. It does to C++ what
+jMock/EasyMock does to Java (well, more or less).
+
+When using gMock,
+
+1.  first, you use some simple macros to describe the interface you want to
+    mock, and they will expand to the implementation of your mock class;
+2.  next, you create some mock objects and specify its expectations and behavior
+    using an intuitive syntax;
+3.  then you exercise code that uses the mock objects. gMock will catch any
+    violation to the expectations as soon as it arises.
+
+## Why gMock?
+
+While mock objects help you remove unnecessary dependencies in tests and make
+them fast and reliable, using mocks manually in C++ is *hard*:
+
+*   Someone has to implement the mocks. The job is usually tedious and
+    error-prone. No wonder people go great distance to avoid it.
+*   The quality of those manually written mocks is a bit, uh, unpredictable. You
+    may see some really polished ones, but you may also see some that were
+    hacked up in a hurry and have all sorts of ad hoc restrictions.
+*   The knowledge you gained from using one mock doesn't transfer to the next
+    one.
+
+In contrast, Java and Python programmers have some fine mock frameworks (jMock,
+EasyMock, [Mox](http://wtf/mox), etc), which automate the creation of mocks. As
+a result, mocking is a proven effective technique and widely adopted practice in
+those communities. Having the right tool absolutely makes the difference.
+
+gMock was built to help C++ programmers. It was inspired by jMock and EasyMock,
+but designed with C++'s specifics in mind. It is your friend if any of the
+following problems is bothering you:
+
+*   You are stuck with a sub-optimal design and wish you had done more
+    prototyping before it was too late, but prototyping in C++ is by no means
+    "rapid".
+*   Your tests are slow as they depend on too many libraries or use expensive
+    resources (e.g. a database).
+*   Your tests are brittle as some resources they use are unreliable (e.g. the
+    network).
+*   You want to test how your code handles a failure (e.g. a file checksum
+    error), but it's not easy to cause one.
+*   You need to make sure that your module interacts with other modules in the
+    right way, but it's hard to observe the interaction; therefore you resort to
+    observing the side effects at the end of the action, but it's awkward at
+    best.
+*   You want to "mock out" your dependencies, except that they don't have mock
+    implementations yet; and, frankly, you aren't thrilled by some of those
+    hand-written mocks.
+
+We encourage you to use gMock as
+
+*   a *design* tool, for it lets you experiment with your interface design early
+    and often. More iterations lead to better designs!
+*   a *testing* tool to cut your tests' outbound dependencies and probe the
+    interaction between your module and its collaborators.
+
+## Getting Started
+
+gMock is bundled with googletest.
+
+## A Case for Mock Turtles
+
+Let's look at an example. Suppose you are developing a graphics program that
+relies on a [LOGO](http://en.wikipedia.org/wiki/Logo_programming_language)-like
+API for drawing. How would you test that it does the right thing? Well, you can
+run it and compare the screen with a golden screen snapshot, but let's admit it:
+tests like this are expensive to run and fragile (What if you just upgraded to a
+shiny new graphics card that has better anti-aliasing? Suddenly you have to
+update all your golden images.). It would be too painful if all your tests are
+like this. Fortunately, you learned about
+[Dependency Injection](http://en.wikipedia.org/wiki/Dependency_injection) and know the right thing
+to do: instead of having your application talk to the system API directly, wrap
+the API in an interface (say, `Turtle`) and code to that interface:
+
+```cpp
+class Turtle {
+  ...
+  virtual ~Turtle() {}
+  virtual void PenUp() = 0;
+  virtual void PenDown() = 0;
+  virtual void Forward(int distance) = 0;
+  virtual void Turn(int degrees) = 0;
+  virtual void GoTo(int x, int y) = 0;
+  virtual int GetX() const = 0;
+  virtual int GetY() const = 0;
+};
+```
+
+(Note that the destructor of `Turtle` **must** be virtual, as is the case for
+**all** classes you intend to inherit from - otherwise the destructor of the
+derived class will not be called when you delete an object through a base
+pointer, and you'll get corrupted program states like memory leaks.)
+
+You can control whether the turtle's movement will leave a trace using `PenUp()`
+and `PenDown()`, and control its movement using `Forward()`, `Turn()`, and
+`GoTo()`. Finally, `GetX()` and `GetY()` tell you the current position of the
+turtle.
+
+Your program will normally use a real implementation of this interface. In
+tests, you can use a mock implementation instead. This allows you to easily
+check what drawing primitives your program is calling, with what arguments, and
+in which order. Tests written this way are much more robust (they won't break
+because your new machine does anti-aliasing differently), easier to read and
+maintain (the intent of a test is expressed in the code, not in some binary
+images), and run *much, much faster*.
+
+## Writing the Mock Class
+
+If you are lucky, the mocks you need to use have already been implemented by
+some nice people. If, however, you find yourself in the position to write a mock
+class, relax - gMock turns this task into a fun game! (Well, almost.)
+
+### How to Define It
+
+Using the `Turtle` interface as example, here are the simple steps you need to
+follow:
+
+*   Derive a class `MockTurtle` from `Turtle`.
+*   Take a *virtual* function of `Turtle` (while it's possible to
+    [mock non-virtual methods using templates](gmock_cook_book.md#MockingNonVirtualMethods),
+    it's much more involved).
+*   In the `public:` section of the child class, write `MOCK_METHOD();`
+*   Now comes the fun part: you take the function signature, cut-and-paste it
+    into the macro, and add two commas - one between the return type and the
+    name, another between the name and the argument list.
+*   If you're mocking a const method, add a 4th parameter containing `(const)`
+    (the parentheses are required).
+*   Since you're overriding a virtual method, we suggest adding the `override`
+    keyword. For const methods the 4th parameter becomes `(const, override)`,
+    for non-const methods just `(override)`. This isn't mandatory.
+*   Repeat until all virtual functions you want to mock are done. (It goes
+    without saying that *all* pure virtual methods in your abstract class must
+    be either mocked or overridden.)
+
+After the process, you should have something like:
+
+```cpp
+#include "gmock/gmock.h"  // Brings in gMock.
+
+class MockTurtle : public Turtle {
+ public:
+  ...
+  MOCK_METHOD(void, PenUp, (), (override));
+  MOCK_METHOD(void, PenDown, (), (override));
+  MOCK_METHOD(void, Forward, (int distance), (override));
+  MOCK_METHOD(void, Turn, (int degrees), (override));
+  MOCK_METHOD(void, GoTo, (int x, int y), (override));
+  MOCK_METHOD(int, GetX, (), (const, override));
+  MOCK_METHOD(int, GetY, (), (const, override));
+};
+```
+
+You don't need to define these mock methods somewhere else - the `MOCK_METHOD`
+macro will generate the definitions for you. It's that simple!
+
+### Where to Put It
+
+When you define a mock class, you need to decide where to put its definition.
+Some people put it in a `_test.cc`. This is fine when the interface being mocked
+(say, `Foo`) is owned by the same person or team. Otherwise, when the owner of
+`Foo` changes it, your test could break. (You can't really expect `Foo`'s
+maintainer to fix every test that uses `Foo`, can you?)
+
+So, the rule of thumb is: if you need to mock `Foo` and it's owned by others,
+define the mock class in `Foo`'s package (better, in a `testing` sub-package
+such that you can clearly separate production code and testing utilities), put
+it in a `.h` and a `cc_library`. Then everyone can reference them from their
+tests. If `Foo` ever changes, there is only one copy of `MockFoo` to change, and
+only tests that depend on the changed methods need to be fixed.
+
+Another way to do it: you can introduce a thin layer `FooAdaptor` on top of
+`Foo` and code to this new interface. Since you own `FooAdaptor`, you can absorb
+changes in `Foo` much more easily. While this is more work initially, carefully
+choosing the adaptor interface can make your code easier to write and more
+readable (a net win in the long run), as you can choose `FooAdaptor` to fit your
+specific domain much better than `Foo` does.
+
+<!-- GOOGLETEST_CM0029 DO NOT DELETE -->
+
+## Using Mocks in Tests
+
+Once you have a mock class, using it is easy. The typical work flow is:
+
+1.  Import the gMock names from the `testing` namespace such that you can use
+    them unqualified (You only have to do it once per file). Remember that
+    namespaces are a good idea.
+2.  Create some mock objects.
+3.  Specify your expectations on them (How many times will a method be called?
+    With what arguments? What should it do? etc.).
+4.  Exercise some code that uses the mocks; optionally, check the result using
+    googletest assertions. If a mock method is called more than expected or with
+    wrong arguments, you'll get an error immediately.
+5.  When a mock is destructed, gMock will automatically check whether all
+    expectations on it have been satisfied.
+
+Here's an example:
+
+```cpp
+#include "path/to/mock-turtle.h"
+#include "gmock/gmock.h"
+#include "gtest/gtest.h"
+
+using ::testing::AtLeast;                         // #1
+
+TEST(PainterTest, CanDrawSomething) {
+  MockTurtle turtle;                              // #2
+  EXPECT_CALL(turtle, PenDown())                  // #3
+      .Times(AtLeast(1));
+
+  Painter painter(&turtle);                       // #4
+
+  EXPECT_TRUE(painter.DrawCircle(0, 0, 10));      // #5
+}
+```
+
+As you might have guessed, this test checks that `PenDown()` is called at least
+once. If the `painter` object didn't call this method, your test will fail with
+a message like this:
+
+```text
+path/to/my_test.cc:119: Failure
+Actual function call count doesn't match this expectation:
+Actually: never called;
+Expected: called at least once.
+Stack trace:
+...
+```
+
+**Tip 1:** If you run the test from an Emacs buffer, you can hit `<Enter>` on
+the line number to jump right to the failed expectation.
+
+**Tip 2:** If your mock objects are never deleted, the final verification won't
+happen. Therefore it's a good idea to turn on the heap checker in your tests
+when you allocate mocks on the heap. You get that automatically if you use the
+`gtest_main` library already.
+
+**Important note:** gMock requires expectations to be set **before** the mock
+functions are called, otherwise the behavior is **undefined**. In particular,
+you mustn't interleave `EXPECT_CALL()s` and calls to the mock functions.
+
+This means `EXPECT_CALL()` should be read as expecting that a call will occur
+*in the future*, not that a call has occurred. Why does gMock work like that?
+Well, specifying the expectation beforehand allows gMock to report a violation
+as soon as it rises, when the context (stack trace, etc) is still available.
+This makes debugging much easier.
+
+Admittedly, this test is contrived and doesn't do much. You can easily achieve
+the same effect without using gMock. However, as we shall reveal soon, gMock
+allows you to do *so much more* with the mocks.
+
+## Setting Expectations
+
+The key to using a mock object successfully is to set the *right expectations*
+on it. If you set the expectations too strict, your test will fail as the result
+of unrelated changes. If you set them too loose, bugs can slip through. You want
+to do it just right such that your test can catch exactly the kind of bugs you
+intend it to catch. gMock provides the necessary means for you to do it "just
+right."
+
+### General Syntax
+
+In gMock we use the `EXPECT_CALL()` macro to set an expectation on a mock
+method. The general syntax is:
+
+```cpp
+EXPECT_CALL(mock_object, method(matchers))
+    .Times(cardinality)
+    .WillOnce(action)
+    .WillRepeatedly(action);
+```
+
+The macro has two arguments: first the mock object, and then the method and its
+arguments. Note that the two are separated by a comma (`,`), not a period (`.`).
+(Why using a comma? The answer is that it was necessary for technical reasons.)
+If the method is not overloaded, the macro can also be called without matchers:
+
+```cpp
+EXPECT_CALL(mock_object, non-overloaded-method)
+    .Times(cardinality)
+    .WillOnce(action)
+    .WillRepeatedly(action);
+```
+
+This syntax allows the test writer to specify "called with any arguments"
+without explicitly specifying the number or types of arguments. To avoid
+unintended ambiguity, this syntax may only be used for methods which are not
+overloaded
+
+Either form of the macro can be followed by some optional *clauses* that provide
+more information about the expectation. We'll discuss how each clause works in
+the coming sections.
+
+This syntax is designed to make an expectation read like English. For example,
+you can probably guess that
+
+```cpp
+using ::testing::Return;
+...
+EXPECT_CALL(turtle, GetX())
+    .Times(5)
+    .WillOnce(Return(100))
+    .WillOnce(Return(150))
+    .WillRepeatedly(Return(200));
+```
+
+says that the `turtle` object's `GetX()` method will be called five times, it
+will return 100 the first time, 150 the second time, and then 200 every time.
+Some people like to call this style of syntax a Domain-Specific Language (DSL).
+
+**Note:** Why do we use a macro to do this? Well it serves two purposes: first
+it makes expectations easily identifiable (either by `gsearch` or by a human
+reader), and second it allows gMock to include the source file location of a
+failed expectation in messages, making debugging easier.
+
+### Matchers: What Arguments Do We Expect?
+
+When a mock function takes arguments, we may specify what arguments we are
+expecting, for example:
+
+```cpp
+// Expects the turtle to move forward by 100 units.
+EXPECT_CALL(turtle, Forward(100));
+```
+
+Oftentimes you do not want to be too specific. Remember that talk about tests
+being too rigid? Over specification leads to brittle tests and obscures the
+intent of tests. Therefore we encourage you to specify only what's necessary—no
+more, no less. If you aren't interested in the value of an argument, write `_`
+as the argument, which means "anything goes":
+
+```cpp
+using ::testing::_;
+...
+// Expects that the turtle jumps to somewhere on the x=50 line.
+EXPECT_CALL(turtle, GoTo(50, _));
+```
+
+`_` is an instance of what we call **matchers**. A matcher is like a predicate
+and can test whether an argument is what we'd expect. You can use a matcher
+inside `EXPECT_CALL()` wherever a function argument is expected. `_` is a
+convenient way of saying "any value".
+
+In the above examples, `100` and `50` are also matchers; implicitly, they are
+the same as `Eq(100)` and `Eq(50)`, which specify that the argument must be
+equal (using `operator==`) to the matcher argument. There are many
+[built-in matchers](gmock_cheat_sheet.md#MatcherList) for common types (as well
+as [custom matchers](gmock_cook_book.md#NewMatchers)); for example:
+
+```cpp
+using ::testing::Ge;
+...
+// Expects the turtle moves forward by at least 100.
+EXPECT_CALL(turtle, Forward(Ge(100)));
+```
+
+If you don't care about *any* arguments, rather than specify `_` for each of
+them you may instead omit the parameter list:
+
+```cpp
+// Expects the turtle to move forward.
+EXPECT_CALL(turtle, Forward);
+// Expects the turtle to jump somewhere.
+EXPECT_CALL(turtle, GoTo);
+```
+
+This works for all non-overloaded methods; if a method is overloaded, you need
+to help gMock resolve which overload is expected by specifying the number of
+arguments and possibly also the
+[types of the arguments](gmock_cook_book.md#SelectOverload).
+
+### Cardinalities: How Many Times Will It Be Called?
+
+The first clause we can specify following an `EXPECT_CALL()` is `Times()`. We
+call its argument a **cardinality** as it tells *how many times* the call should
+occur. It allows us to repeat an expectation many times without actually writing
+it as many times. More importantly, a cardinality can be "fuzzy", just like a
+matcher can be. This allows a user to express the intent of a test exactly.
+
+An interesting special case is when we say `Times(0)`. You may have guessed - it
+means that the function shouldn't be called with the given arguments at all, and
+gMock will report a googletest failure whenever the function is (wrongfully)
+called.
+
+We've seen `AtLeast(n)` as an example of fuzzy cardinalities earlier. For the
+list of built-in cardinalities you can use, see
+[here](gmock_cheat_sheet.md#CardinalityList).
+
+The `Times()` clause can be omitted. **If you omit `Times()`, gMock will infer
+the cardinality for you.** The rules are easy to remember:
+
+*   If **neither** `WillOnce()` **nor** `WillRepeatedly()` is in the
+    `EXPECT_CALL()`, the inferred cardinality is `Times(1)`.
+*   If there are *n* `WillOnce()`'s but **no** `WillRepeatedly()`, where *n* >=
+    1, the cardinality is `Times(n)`.
+*   If there are *n* `WillOnce()`'s and **one** `WillRepeatedly()`, where *n* >=
+    0, the cardinality is `Times(AtLeast(n))`.
+
+**Quick quiz:** what do you think will happen if a function is expected to be
+called twice but actually called four times?
+
+### Actions: What Should It Do?
+
+Remember that a mock object doesn't really have a working implementation? We as
+users have to tell it what to do when a method is invoked. This is easy in
+gMock.
+
+First, if the return type of a mock function is a built-in type or a pointer,
+the function has a **default action** (a `void` function will just return, a
+`bool` function will return `false`, and other functions will return 0). In
+addition, in C++ 11 and above, a mock function whose return type is
+default-constructible (i.e. has a default constructor) has a default action of
+returning a default-constructed value. If you don't say anything, this behavior
+will be used.
+
+Second, if a mock function doesn't have a default action, or the default action
+doesn't suit you, you can specify the action to be taken each time the
+expectation matches using a series of `WillOnce()` clauses followed by an
+optional `WillRepeatedly()`. For example,
+
+```cpp
+using ::testing::Return;
+...
+EXPECT_CALL(turtle, GetX())
+     .WillOnce(Return(100))
+     .WillOnce(Return(200))
+     .WillOnce(Return(300));
+```
+
+says that `turtle.GetX()` will be called *exactly three times* (gMock inferred
+this from how many `WillOnce()` clauses we've written, since we didn't
+explicitly write `Times()`), and will return 100, 200, and 300 respectively.
+
+```cpp
+using ::testing::Return;
+...
+EXPECT_CALL(turtle, GetY())
+     .WillOnce(Return(100))
+     .WillOnce(Return(200))
+     .WillRepeatedly(Return(300));
+```
+
+says that `turtle.GetY()` will be called *at least twice* (gMock knows this as
+we've written two `WillOnce()` clauses and a `WillRepeatedly()` while having no
+explicit `Times()`), will return 100 and 200 respectively the first two times,
+and 300 from the third time on.
+
+Of course, if you explicitly write a `Times()`, gMock will not try to infer the
+cardinality itself. What if the number you specified is larger than there are
+`WillOnce()` clauses? Well, after all `WillOnce()`s are used up, gMock will do
+the *default* action for the function every time (unless, of course, you have a
+`WillRepeatedly()`.).
+
+What can we do inside `WillOnce()` besides `Return()`? You can return a
+reference using `ReturnRef(*variable*)`, or invoke a pre-defined function, among
+[others](gmock_cook_book.md#using-actions).
+
+**Important note:** The `EXPECT_CALL()` statement evaluates the action clause
+only once, even though the action may be performed many times. Therefore you
+must be careful about side effects. The following may not do what you want:
+
+```cpp
+using ::testing::Return;
+...
+int n = 100;
+EXPECT_CALL(turtle, GetX())
+    .Times(4)
+    .WillRepeatedly(Return(n++));
+```
+
+Instead of returning 100, 101, 102, ..., consecutively, this mock function will
+always return 100 as `n++` is only evaluated once. Similarly, `Return(new Foo)`
+will create a new `Foo` object when the `EXPECT_CALL()` is executed, and will
+return the same pointer every time. If you want the side effect to happen every
+time, you need to define a custom action, which we'll teach in the
+[cook book](http://<!-- GOOGLETEST_CM0012 DO NOT DELETE -->).
+
+Time for another quiz! What do you think the following means?
+
+```cpp
+using ::testing::Return;
+...
+EXPECT_CALL(turtle, GetY())
+    .Times(4)
+    .WillOnce(Return(100));
+```
+
+Obviously `turtle.GetY()` is expected to be called four times. But if you think
+it will return 100 every time, think twice! Remember that one `WillOnce()`
+clause will be consumed each time the function is invoked and the default action
+will be taken afterwards. So the right answer is that `turtle.GetY()` will
+return 100 the first time, but **return 0 from the second time on**, as
+returning 0 is the default action for `int` functions.
+
+### Using Multiple Expectations {#MultiExpectations}
+
+So far we've only shown examples where you have a single expectation. More
+realistically, you'll specify expectations on multiple mock methods which may be
+from multiple mock objects.
+
+By default, when a mock method is invoked, gMock will search the expectations in
+the **reverse order** they are defined, and stop when an active expectation that
+matches the arguments is found (you can think of it as "newer rules override
+older ones."). If the matching expectation cannot take any more calls, you will
+get an upper-bound-violated failure. Here's an example:
+
+```cpp
+using ::testing::_;
+...
+EXPECT_CALL(turtle, Forward(_));  // #1
+EXPECT_CALL(turtle, Forward(10))  // #2
+    .Times(2);
+```
+
+If `Forward(10)` is called three times in a row, the third time it will be an
+error, as the last matching expectation (#2) has been saturated. If, however,
+the third `Forward(10)` call is replaced by `Forward(20)`, then it would be OK,
+as now #1 will be the matching expectation.
+
+**Note:** Why does gMock search for a match in the *reverse* order of the
+expectations? The reason is that this allows a user to set up the default
+expectations in a mock object's constructor or the test fixture's set-up phase
+and then customize the mock by writing more specific expectations in the test
+body. So, if you have two expectations on the same method, you want to put the
+one with more specific matchers **after** the other, or the more specific rule
+would be shadowed by the more general one that comes after it.
+
+**Tip:** It is very common to start with a catch-all expectation for a method
+and `Times(AnyNumber())` (omitting arguments, or with `_` for all arguments, if
+overloaded). This makes any calls to the method expected. This is not necessary
+for methods that are not mentioned at all (these are "uninteresting"), but is
+useful for methods that have some expectations, but for which other calls are
+ok. See
+[Understanding Uninteresting vs Unexpected Calls](gmock_cook_book.md#uninteresting-vs-unexpected).
+
+### Ordered vs Unordered Calls {#OrderedCalls}
+
+By default, an expectation can match a call even though an earlier expectation
+hasn't been satisfied. In other words, the calls don't have to occur in the
+order the expectations are specified.
+
+Sometimes, you may want all the expected calls to occur in a strict order. To
+say this in gMock is easy:
+
+```cpp
+using ::testing::InSequence;
+...
+TEST(FooTest, DrawsLineSegment) {
+  ...
+  {
+    InSequence seq;
+
+    EXPECT_CALL(turtle, PenDown());
+    EXPECT_CALL(turtle, Forward(100));
+    EXPECT_CALL(turtle, PenUp());
+  }
+  Foo();
+}
+```
+
+By creating an object of type `InSequence`, all expectations in its scope are
+put into a *sequence* and have to occur *sequentially*. Since we are just
+relying on the constructor and destructor of this object to do the actual work,
+its name is really irrelevant.
+
+In this example, we test that `Foo()` calls the three expected functions in the
+order as written. If a call is made out-of-order, it will be an error.
+
+(What if you care about the relative order of some of the calls, but not all of
+them? Can you specify an arbitrary partial order? The answer is ... yes! The
+details can be found [here](gmock_cook_book.md#OrderedCalls).)
+
+### All Expectations Are Sticky (Unless Said Otherwise) {#StickyExpectations}
+
+Now let's do a quick quiz to see how well you can use this mock stuff already.
+How would you test that the turtle is asked to go to the origin *exactly twice*
+(you want to ignore any other instructions it receives)?
+
+After you've come up with your answer, take a look at ours and compare notes
+(solve it yourself first - don't cheat!):
+
+```cpp
+using ::testing::_;
+using ::testing::AnyNumber;
+...
+EXPECT_CALL(turtle, GoTo(_, _))  // #1
+     .Times(AnyNumber());
+EXPECT_CALL(turtle, GoTo(0, 0))  // #2
+     .Times(2);
+```
+
+Suppose `turtle.GoTo(0, 0)` is called three times. In the third time, gMock will
+see that the arguments match expectation #2 (remember that we always pick the
+last matching expectation). Now, since we said that there should be only two
+such calls, gMock will report an error immediately. This is basically what we've
+told you in the [Using Multiple Expectations](#MultiExpectations) section above.
+
+This example shows that **expectations in gMock are "sticky" by default**, in
+the sense that they remain active even after we have reached their invocation
+upper bounds. This is an important rule to remember, as it affects the meaning
+of the spec, and is **different** to how it's done in many other mocking
+frameworks (Why'd we do that? Because we think our rule makes the common cases
+easier to express and understand.).
+
+Simple? Let's see if you've really understood it: what does the following code
+say?
+
+```cpp
+using ::testing::Return;
+...
+for (int i = n; i > 0; i--) {
+  EXPECT_CALL(turtle, GetX())
+      .WillOnce(Return(10*i));
+}
+```
+
+If you think it says that `turtle.GetX()` will be called `n` times and will
+return 10, 20, 30, ..., consecutively, think twice! The problem is that, as we
+said, expectations are sticky. So, the second time `turtle.GetX()` is called,
+the last (latest) `EXPECT_CALL()` statement will match, and will immediately
+lead to an "upper bound violated" error - this piece of code is not very useful!
+
+One correct way of saying that `turtle.GetX()` will return 10, 20, 30, ..., is
+to explicitly say that the expectations are *not* sticky. In other words, they
+should *retire* as soon as they are saturated:
+
+```cpp
+using ::testing::Return;
+...
+for (int i = n; i > 0; i--) {
+  EXPECT_CALL(turtle, GetX())
+      .WillOnce(Return(10*i))
+      .RetiresOnSaturation();
+}
+```
+
+And, there's a better way to do it: in this case, we expect the calls to occur
+in a specific order, and we line up the actions to match the order. Since the
+order is important here, we should make it explicit using a sequence:
+
+```cpp
+using ::testing::InSequence;
+using ::testing::Return;
+...
+{
+  InSequence s;
+
+  for (int i = 1; i <= n; i++) {
+    EXPECT_CALL(turtle, GetX())
+        .WillOnce(Return(10*i))
+        .RetiresOnSaturation();
+  }
+}
+```
+
+By the way, the other situation where an expectation may *not* be sticky is when
+it's in a sequence - as soon as another expectation that comes after it in the
+sequence has been used, it automatically retires (and will never be used to
+match any call).
+
+### Uninteresting Calls
+
+A mock object may have many methods, and not all of them are that interesting.
+For example, in some tests we may not care about how many times `GetX()` and
+`GetY()` get called.
+
+In gMock, if you are not interested in a method, just don't say anything about
+it. If a call to this method occurs, you'll see a warning in the test output,
+but it won't be a failure. This is called "naggy" behavior; to change, see
+[The Nice, the Strict, and the Naggy](gmock_cook_book.md#NiceStrictNaggy).