C++ unit tests with googletest

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Unit tests with googletest

Unit tests let programmer know that his software works as expected. If you i have ever done heavy development or you are planning to do so, you would definitely see the obvious advantages of unit testing your software:

  • you can easily check if software works on different platforms;

  • unit tests might replace or at least supplement the samples;

  • you can assert if your code still works after refactoring;

  • unit tests can also be used to test and track performance;

  • tests can be run automatically and periodically;

  • unit tests make you try module/library API before integrating it to the other code - this way design issues can be noticed sooner;

  • unit tests inspire confidence;

  • and many more advantages...

One of the many testing frameworks for C++ if googletest. Let's see how to write unit tests for your modules.

Setup environment

We'll use googletest, CMake and debian 7.3 system. Get the prerequisites:

$ sudo apt-get install cmake unzip

Download the latest googletest version from here (by the time I wrote this article it was v1.7.0).

Unpack the package:

$ unzip gtest-1.7.0.zip

Create sample project

You can get a sample from github:

$ git clone https://github.com/povilasb-com/cpp-googletest-intro.git

Sample project directory tree:

.
|__ googletest-cmake
  |__ lib
  | |__ googletest -> ~/dev-tools/gtest-1.7.0
  |__ src
  | |__ lib1.cpp
  | |__ lib1.hpp
  |__ test
  | |__ lib1_test.cpp
  |__ CMakeLists.txt
  |__ Makefile

Create directory hierarchy

$ mkdir googletest-cmake
$ cd googletest-cmake
$ mkdir lib src test

Write sample functions that will be tested

cpp-googletest-cmake/src/lib1.hpp:

#ifndef _LIB1_H
#define _LIB1_H 1
int sum(int n1, int n2);
int mul(int n1, int n2);
#endif

cpp-googletest-cmake/src/lib1.cpp:

#include "lib1.hpp"
int
sum(int n1, int n2)
{
        return n1 + n2;
}
int
mul(int n1, int n2)
{
        return n1 * n2;
}

Create build scripts

googletest-cmake/src/CMakeLists.txt:

cmake_minimum_required (VERSION 2.6)
project (Lib1 CXX)
set (CMAKE_CXX_FLAGS "-ggdb")
set (SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/src")
include_directories ("${SRC_DIR}")
file (GLOB_RECURSE SRC_FILES "${SRC_DIR}/*.cpp")
# Compiles static lib that will be linked with tests.
set (LIB_NAME "lib1")
add_library ("${LIB_NAME}" STATIC ${SRC_FILES})
# Include googletest.
set (GTEST_DIR "${CMAKE_CURRENT_SOURCE_DIR}/lib/googletest")
add_subdirectory (${GTEST_DIR})
include_directories ("${GTEST_DIR}/include")
# Build tests executable.
set (TEST_EXEC "${LIB_NAME}_test")
set (TEST_SRC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/test")
file (GLOB_RECURSE TEST_SRC_FILES "${TEST_SRC_DIR}/*.cpp")
add_executable ("${TEST_EXEC}" ${TEST_SRC_FILES})
target_link_libraries ("${TEST_EXEC}" "${LIB_NAME}" "gtest" "gtest_main")

CMake does the main build process, but we also use a helper Makefile that runs cmake and the compiled tests executable.

googletes-cmake/src/Makefile:

BUILD_DIR = build
all: test test-run
test: $(BUILD_DIR)
        cd $(BUILD_DIR); cmake $(CURDIR); make
test-run:
        $(BUILD_DIR)/lib1_test
$(BUILD_DIR):
        mkdir -p $@
clean:
        rm -rf $(BUILD_DIR)
.PHONY: all test test-run clean

Create test suite

googletes-cmake/test/lib1_test.cpp:

#include <gtest/gtest.h>
#include "lib1.hpp"
TEST(lib1, sum)
{
        int s = sum(10, 15);
        ASSERT_TRUE(s == 25);
}
TEST(lib1, mul)
{
        int m = mul(10, 15);
        ASSERT_TRUE(m == 150);
}

This is the simplest form of the unit tests. It uses ASSERT_TRUE macro which checks if the specified expression is true. If it is not the test execution is terminated.

There are more convenience macros that you can use to assert expected values: https://code.google.com/p/googletest/wiki/V1_7_Primer.

Run tests

Simply type make in project directory. It invokes the helper Makefile that runs CMake which builds the tests executable and then Makefile runs this executable.

Successfull execution results

/images/gtest_ok.png

Example of tests failure

/images/gtest_fail.png

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