Writing unit tests for C++ with Bazel and GoogleTest

For last couple of months I am in love with writing Unit Tests. I wasn’t like that. You may say I was adventurous, hardcore and love living dangerous life! But that wasn’t the case, believe me. I was just plain dumb. So how was my life before I started writing Unit Tests?

I was so afraid to refactor my codes. There is a high possibility it may break something else in somewhere that I will not be able to detect soon. But eventually when I will do, it will be very hard to trace why it is broken and fix it. Nobody around me told me to write Unit Tests and few who did, didn’t even write Unit Tests for themselves! It was like Aesob’s The Two Crabs story I read at my childhood.

Although I did some C++ codes in University and attended some Programming Competition where I’ve used C++ for writing code, but I never did Object Oriented Programming with C++. So few months ago I have started learning C++ in my free time. At first I tried to use CMAKE to build. After using it for sometime, I found Bazel. It is faster, more organized and modular.

At first lets look at the folder structure-

│   gmock.BUILD
│   WORKSPACE
│
├───src
│   ├───lib
│   │       BUILD
│   │       Greeting.cc
│   │       Greeting.h
│   │
│   └───main
│           BUILD
│           main.cc
│
└───tests
        BUILD
        Greeting_test.cc

There should be a WORKSPACE file in the root of your source code. It contains external dependencies. If you don’t have any external dependencies in your project, your WORKSPACE file should be empty, But you must have this file.

We are using GoogleTest as external dependency. Lets look inside our WORKSPACE file-

new_git_repository(
    name = "googletest",
    build_file = "gmock.BUILD",
    remote = "https://github.com/google/googletest",
    tag = "release-1.8.0",
)

Here, the dependency is added as a git repository. As a result, when we build the project, it will download the git repository and run the build_file gmock.BUILD to build the GoogleTest library, which we will import in our tests. The content of the gmock.BUILD file is-

cc_library(
    name = "gtest",
    srcs = [
        "googletest/src/gtest-all.cc",
        "googlemock/src/gmock-all.cc",
    ],
    hdrs = glob([
        "**/*.h",
        "googletest/src/*.cc",
        "googlemock/src/*.cc",
    ]),
    includes = [
        "googlemock",
        "googletest",
        "googletest/include",
        "googlemock/include",
    ],
    linkopts = ["-pthread"],
    visibility = ["//visibility:public"],
)

cc_library(
    name = "gtest_main",
    srcs = ["googlemock/src/gmock_main.cc"],
    linkopts = ["-pthread"],
    visibility = ["//visibility:public"],
    deps = [":gtest"],
)

This concludes our initial setup of GoogleTest with Bazel. Now we need to add @googletest//:gtest_main as a dependency of our test library, cc_test and import gtest/gtest.h to our unit test file. Example BUILD file tests -

cc_test(
    name = "tests",
    srcs = glob(["**/*.cc"]),
    deps = [
        "//src/lib:GreetingLib",
        "@googletest//:gtest_main",
    ],
)

Here the first dependency is cc_library dependency, where we have a Greeting class that have a public method, getGreetingMessage() that return Hello World!.

And content of the greeting_test.cc-

#include "gtest/gtest.h"
#include "src/lib/Greeting.h"

TEST(GreetingShould, ReturnHelloWorld){
    Greeting *greet = new Greeting();
    std::string actual = greet->getGreetingMessage();
    std::string expected = "Hello World!";
    EXPECT_EQ(expected, actual);
}

Building and Running unit tests

Building the gradle project is easy. You just need to run-

$ bazel build ...

to build every cc_library and cc_binary of the project. And to run all unit tests just run-

$ bazel test ...

I have created a git repository , which you can clone and use as your starting point. Please feel free to star it if you think my repository helps you.

CPP-Template