Notes From My GoogleTest Demo

I recently gave a demo of GoogleTest at Kjeller Software Community / Oslo C++ Users Group. These are the notes from my demo. My apologies to those who did not attend, these might not make much sense unless you saw the demo.


See my post about installation and setup of GoogleTest in your project.

Test types

TEST(TestCaseName, TestName)
A single test TestName belonging to the TestCaseName test case. The TEST macro converts this into class TestCaseName_TestName

TEST_F(TestFixtureName, TestName)
A single test TestName belonging to the TestFixtureName test case, which uses a fixture. The TEST_F macro converts this into class TestFixtureName_TestName : public TestFixtureName. You need to implement the TestFixtureName : public ::testing::Test class also.

TEST_P(TestFixtureName, TestName)
A single parametrized test TestName belonging to the TestFixtureName test case, which uses a fixture with a parametrized interface. You need to implement the TestFixtureName : public ::testing::WithParamInterface class also. Use GetParam() to get the parameter, and INSTANTIATE_TEST_CASE_P to instantiate tests.

Finally remember that you can use SetUp() and TearDown(), but might just as well use the plain constructor and destructor. A reason to use TearDown() instead of the destructor is if it might throw an exception (which destructors should not do).


Here are some examples of assertions:

You can also write your own assertion functions:
AssertionResult predicateFunction(...)

Or just write a void function that does all the asserts internally:
void assertWhatever()

Some final tips

Use one test project per production project, for instance NoFlyListTest for NoFlyList. This makes it easy to find the tests for a project. If the rest of your code is decoupled, it might also speed up linking a lot, since you only need to link the test project, and not your entire solution. This especially helps if you are doing TDD, in which you will typically compile and link several times a minute.

Write short tests, and only test one thing per test. This will make it easy to figure out what went wrong when tests break in the future.

Write tests before you implement the code that passes them. This will verify that the test didn’t pass just by accident. It will also let you see how the failing test looks like, so you can make sure it is self-explanatory enough that someone will understand what went wrong when it breaks.

Don’t be a terrorist, you’ll end up in a bad place.

Source Code

If you want to have a look at the code from my Kjeller Software Community demo, it is available on GitHub.

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Installing and Using GoogleTest with Visual Studio

Important note: This blog post is one of the top hits on Google for “googletest visual studio”. It is however quite old, and might no longer reflect the best way to use GoogleTest with Visual Studio. 

Google C++ Testing Framework (aka. GoogleTest) is a unittesting framework for C++. This post describes how to install it, and set it up in your project. I am using GoogleTest 1.6.0 here, but other versions should be similar. The instructions provided are for Visual Studio 2010, but 2012 should be exactly the same.


First of all, download the latest version from the GoogleTest download page, and unzip it. Inside, you will find a directory called msvc, which contains the Visual Studio solutions:

In this directory, you will find two solutions, gtest.sln, and gtest-md.sln. Which one you want depends on whether you are using a static or dynamic runtime. If you are unsure which one to use, take a look in your existing solution:

If you are using the DLL version of the runtime, use the gtest-md.sln solution, otherwise use gtest.sln. Before you open the solution though, make sure it is not read only, as Visual Studio will want to convert it to your version:

Open the solution you want, agree to convert the solution. Make sure you build it both in Debug and Release versions. The resulting libraries end up in gtest-1.6.0\msvc\gtest\Debug and gtest-1.6.0\msvc\gtest\Release, respectively. This is a good time to copy the libraries to wherever you keep libraries for your projects. The files you will need are gtestd.lib and gtest_maind.lib from the Debug directory, and gtest.lib and gtest_main.lib from the Release directory. In addition, you need all the headers from gtest-1.6.0\include. (Of course, you could just copy the entire gtest-1.6.0 directory and not care about which files you need.)

Setup for Your Project

I suggest to use one test project per production project. This makes it easy to find the tests you are looking for. Also, if your code is nicely decoupled, you might be able to link just these two projects, and not your entire solution. This can speed up your “red-green-refactor” cycle considerably. Finally, this makes it easy to exclude your test code from the final binary you ship. Here is an example from my Kjeller Software Community presentation:

Set the following properties for your test project:

  • Make sure to set up the test project to use the same runtime library as your production project (MT / MTd / MD / MDd).
  • Add an additional include directory c:\wherever\you\put\gtest\include
  • Add an additional library directory c:\wherever\you\put\the\libs
  • Under Linker -> Input , add a dependency on gtest.lib for your Release configuration, and gtestd.lib for your Debug configuration. Unless you want to write your own main function that runs all the tests, also add a dependency on gtest_main.lib / gtest_maind.lib, respectively. This will add a main() method to your project which discovers and runs all the tests.
  • Under Properties -> Linker -> System, set SubSystem to Console, to keep the test-window open after the tests have run.

Also make sure that your test project depends on the production project:

And that’s it! Now you can start writing and running tests, but since the documentation already describes that pretty well, I will not go into that here. If you want to have a look at the code from my Kjeller Software Community demo, it is available on GitHub.

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New Software Community, and Google Test Demo

Together with Håkon K. Olafsen, I founded Kjeller Software Community earlier this summer. Our first meetup is due this Wednesday (September 26). I will do a demo of Google C++ Testing Framework, aka. GoogleTest, and afterwards we will have a few beers and chat about programming and all things geeky. Hopefully we will also get some good suggestions for future events and meetups. The meetup will happen at Klimt pub in Lillestrøm, at 6:00 pm.

This meetup is done in cooperation with Oslo C++ Users Group, of which I am also a member. If you are into C++, and live in the greater Oslo area, that group is also highly recommended.

Notes from the talk, and a blog post about Google Test will be up later this week.

If you enjoyed this post, you can subscribe to my blog, or follow me on Twitter. You can also follow Kjeller Software Community on Twitter.

Private Inheritance

In which I introduce private inheritance, but discourage its use.

When inheriting in C++, you normally see

class Derived : public Base {};

It’s almost as if public is synonymous to inherits from. But did you know there is also private inheritance, and why you (probably) don’t see it a lot?

When inheriting publicly from a base class, all base members will be accessible from the derived class, with the same accessibility as in the base class. Given these classes:

class Base
    void pub() {}
    void priv() {}

class DerivedPublic : public Base

class DerivedPrivate : private Base

Public inheritance results in this:

    DerivedPublic derivedPublic;;
    //derivedPublic.priv(); //error: ‘void Base::priv()’ is private

Whereas private inheritance results in this:

    DerivedPrivate derivedPrivate;
    //; //error: ‘void Base::pub()’ is inaccessible
    //derivedPrivate.priv(); //error: ‘void Base::priv()’ is private

So why would you want to inherit privately? To allow Derived to access the public members of Base, without exposing them to the users of Derived.

Inside the class, the members are accessible:

class DerivedPrivate2: private Base
    void foo() { pub(); }

But outside, they are not:

    DerivedPrivate2 derivedPrivate2;;
    //; //error: ‘void Base::pub()’ is inaccessible

But wait a minute, doesn’t this look a whole lot like the good old inheritance (is-a) vs. composition (has-a)? It does indeed! Private inheritance is really a has-a. And in most circumstances composition and private inheritance are interchangeable. However, since inheritance results in stronger coupling, the general recommendation is to choose composition instead. Here is how DerivedPrivate2 would look using composition:

class NotDerived
    void foo() {; }
    Base b;

Now you may be thinking: “But I read somewhere that you need to use private inheritance if you want to override a virtual Base method?” You probably did, and I’ll get back to that in the next post.

As usual, the code for this blog post is available on GitHub.

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C++ Puzzle #1: Initialization Order

Time for another puzzle! What is the output of this program?

class Parent
    Parent(int p=0.0) : p(p)
        cout << "Parent(" << p << ")" << endl;

    int p;

class Member
    Member(int m=0.0) : m(m)
        cout << "Member(" << m << ")" << endl;

    Member& operator=(const Member& rhs)
            cout << "Member is copied" << endl;
            m = rhs.m;
            return *this;

    int m;

class Derived : public Parent
    Derived() : foo(10), bar(foo*2)
        m = Member(42);

    int bar;
    int foo;
    Member m;

int main()
    Derived d;
    cout << d.p << " " << << " " << << " " << d.m.m << endl;

Answer: Undefined behaviour! Which means it could output whatever, crash at any point, or format your hard drive. Can you spot the source of the undefined behaviour? Hint: Look for the use of an uninitialized variable.

Did you see that the order of foo and bar in the initializer list is not in the same order as their declarations? Members are always initialized in the order of declaration, not in the order in the initialization list. This means bar is initialized before foo, using an uninitialized foo to compute its value. If you compile with all warnings enabled (always a good idea), your compiler should warn you about this. For instance, g++ tells me:

main.cpp: In constructor ‘Derived::Derived()’:
main.cpp:29:9: warning: ‘Derived::foo’ will be initialized after [-Wreorder]
main.cpp:28:9: warning:   ‘int Derived::bar’ [-Wreorder]
main.cpp:22:5: warning:   when initialized here [-Wreorder]

Next question then, what is the likely output of this program on a real compiler? On my Ubuntu 12.04 using g++ 4.6, I get:

Member is copied
0 10 8393920 42  

Lets’ walk through what happens here.

  • 1: Derived inherits from Parent. C++ guarantees that all parent objects are fully constructed before the constructor of the derived class is invoked, so the first thing that happens is that the default constructor of Parent is called. (Did I fool you with Parent(7); in the constructor though? That line will just create a local object that is never used. Had I moved it to the initializer list, it would have been used instead of the default constructor.)
  • 2: Before the body of Derived‘s constructor, all its members will be initialized. Since we don’t specifically initialize Member m in the initializer list, it is first automatically default constructed, and then re-assigned in the body of the constructor (as seen in line 5 of the output).
  • 3: On line 34 of the program, we create a local Parent object which is never used. Maybe we meant to set p to 7, but put the Parent() call in the wrong place?
  • 4-5: Now another Member is constructed, and copy assigned to m. All this re-construction and copying could have been avoided if we had moved the call Member(42) to the initializer list.
  • 6: Finally, we have a look at the resulting values of Derived‘s members:
    • p is 0, not 7 as we maybe meant it to be, as explained in 1.
    • foo is 10, hopefully as expected.
    • bar is 8393920, due to the use of the uninitialized foo, as explained earlier. This is entirely by chance, and should not be relied on! Your program might just as well crash, or do something worse.

Finally let’s clean up the program and see what happens. We reorder the declarations of foo and bar, and move all initializations to the initializer list:

ERROR: Couldn't open file: [Errno 2] No such file or directory: '/home/anders/Documents/code/blog/initialization/main2.cpp'

Now the program is well defined, and free of repeated constructors and copying. Here is the output:

7 10 20 42

Much better! Full source here.

As usual, the code for this blog post is available on GitHub.

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