How can I use Google Test with my project that builds via autotools?

Question

It seems like there are a few answers that kind-of, sort-of make sense, but that I don't know how to carry out. And I haven't found a comprehensive answer.

The First Problem

Google Test should not be an installed library, it should be built with the project. (See the FAQ.) As far as I can tell, this means the Google Test libraries are a dependency of my unit tests, and should be built when I run "make check" within my project for the first time. This should build Google Test libraries in some directory. I don't know how to do this. It mentions some autotools script that's deprecated, and I'm not sure what they're talking about or how to point my build at it properly.

The Second Problem

Assuming the build is successful, how do I write a test that uses my locally-compiled version of Google Test to run tests? I assume that there are a bunch of Makefile.am commands I put in my tests directory. But what are they? And what's an example of a unit test that uses Google Test?

Answer 1

I have solved the problem to my satisfaction! I will move on entirely now. This is basically asking for a tutorial. There are a lot of decisions that must be made, hopefully logically, so that Google Test dovetails nicely into autotools. So I apologize in advance for the long answer, but all the details should be there.

The First Problem

In order to understand the answer, the question needs to be rephrased a little. We are compiling Google Test as a library which our test code will link to. The library will not be installed. The question we want to ask is

"How do we configure autotools to compile Google Test as a library which our test code can link against?"

In order to do that, we need to download Google Test and place it into our project. I use Github, so I do that by adding a submodule in the root path of my project:

$ git submodule add [email protected]:google/googletest.git
$ git submodule init
$ git submodule update

This downloads googletest into my root of my project:

/:
    Makefile.am
    configure.ac
    src/:
        (files for my project)
    tests/:
        (test files)
    googletest/:
        googletest/:
            include/:
                (headers, etc., to be included)
                gtest/:
                    gtest.h
            m4/:
                (directory for m4 scripts and things)
            src/:
                (source files for Google Test)

I need to compile per the instructions. I only want the Google Test library to be built upon running make check, so I will use check_LTLIBRARIES. I add the following to my tests Makefile.am in /tests:

check_LTLIBRARIES = libgtest.la
libgtest_la_SOURCES = ../googletest/googletest/src/gtest-all.cc
libgtest_la_CPPFLAGS = -I$(top_srcdir)/googletest/googletest/include -I$(top_srcdir)/googletest/googletest
libgtest_la_LDFLAGS = -pthread

This requires subdir-objects to be enabled in configure.ac. That is accomplished by adding it to the AM_INIT_AUTOMAKE line. I also need to include the makefile in AC_CONFIG_FILES. We also want to use libtool, because we are compiling library files (I'll explain why and how that works in a moment). To use libtool, we add AM_PROG_AR, LT_INIT. We want autoreconf to install m4 macros to /m4, and then we want automake to find them, so we need AC_CONFIG_MACRO_DIRS. My configure.ac has lines updated:

AM_INIT_AUTOMAKE([-Wall -Werror subdir-objects])
...
AM_PROG_AR
LT_INIT
AC_CONFIG_MACRO_DIRS([m4])
...
AC_CONFIG_FILES([Makefile
                 src/Makefile
                 tests/Makefile
                 ])

I also need to include the subdirectory and a line pointing to the macros in the /m4 macros directory in my /Makefile.am:

ACLOCAL_AMFLAGS = -I m4

SUBDIRS = src tests

What has this done? Libtool has been enabled with AM_PROG_AR and LT_INIT. The check_LTLIBRARIES means we will use libtool to create what's called a convenience library called libgtest.la. With subdir-objects enabled, it will be built into the /tests directory, but not installed. This means that, whenever we want to update our tests, we don't have to recompile the Google Test library libgtest.la. This will save time when testing and help us iterate faster. Then, we will want to compile our unit tests against it later as we update them. The library will only be compiled upon running make check, saving time by not compiling it if all we want to do is make or make install.

The Second Problem

Now, the second problem needs to be refined: How do you (a) create a test (b) that is linked to the Google Test libraries and thus uses them? The questions are kind of intertwined, so we answer them at once.

Creating a test is just a matter of putting the following code into a gtest.cpp file located at /tests/gtest.cpp:

#include "gtest/gtest.h" // we will add the path to C preprocessor later

TEST(CategoryTest, SpecificTest)
{
    ASSERT_EQ(0, 0);
}

int main(int argc, char **argv)
{
    ::testing::InitGoogleTest(&argc, argv);

    return RUN_ALL_TESTS();
}

This runs only the simple test 0=0. To create a test for your library, you need to read the primer. You'll notice we don't need a header for this (yet). We are linking to the file "gtest/gtest.h", so we'll need to make sure that we tell automake to include a directory that has gtest/gtest.h.

Next, we need to tell automake that we want to build a test and run it. The test is going to build into an executable that we don't want to install. Then automake is going to run that executable. It will report whether that executable says the tests passed or failed.

Automake does that by looking in the makefile for the variable check_PROGRAMS. These are the programs it will compile, but it won't necessarily run them. So we add to /tests/Makefile.am:

check_PROGRAMS = gtest

gtest_SOURCES = gtest.cpp

gtest_LDADD = libgtest.la

gtest_LDFLAGS = -pthread

gtest_CPPFLAGS = -I$(top_srcdir)/googletest/googletest/include -I$(top_srcdir)/googletest/googletest -pthread

The gtest_SOURCES finds the /tests/gtest.cpp file and compiles it. gtest_LDADD links against libgtest.la which will be compiled into the /tests directory. Google wants us to use the gtest_LDFLAGS line to enable pthreads. Finally, we need to include the location where the header "gtest/gtest.h" will be found, and that is the gtest_CPPFLAGS line. Google also wants us to include the /googletest/googletest location, and include the

The state of things: The Google Test library libgtest.la will compile with make into the directory /tests, but not be installed. The binary gtest will only be compiled with make check, but will not be installed.

Next we want to tell automake to actually run the compiled binary gtest and report errors. This is accomplished by adding a line to /tests/Makefile.am:

TESTS = gtest

The final /tests/Makefile.am looks like this:

check_LTLIBRARIES = libgtest.la
libgtest_la_SOURCES = ../googletest/googletest/src/gtest-all.cc
libgtest_la_CPPFLAGS = -I$(top_srcdir)/googletest/googletest/include -I$(top_srcdir)/googletest/googletest -pthread

check_PROGRAMS = gtest demo

gtest_SOURCES = gtest.cpp ../src/fields.cpp

gtest_LDADD = libgtest.la

gtest_LDFLAGS = -pthread

gtest_CPPFLAGS = -I$(top_srcdir)/googletest/googletest/include -I$(top_srcdir)/src

demo_SOURCES = demo.cpp ../src/fields.cpp

demo_CPPFLAGS = -I$(top_srcdir)/src

TESTS = gtest

Now, autoreconf -fiv (note any errors and hopefully fix them) from /, and make check and you should get a test that runs:

build(dev)$ make check
Making check in tests
/Applications/Xcode.app/Contents/Developer/usr/bin/make  gtest
make[2]: `gtest' is up to date.
/Applications/Xcode.app/Contents/Developer/usr/bin/make  check-TESTS
PASS: gtest
============================================================================
Testsuite summary for IonMotion 0.0.1
============================================================================
# TOTAL: 1
# PASS:  1
# SKIP:  0
# XFAIL: 0
# FAIL:  0
# XPASS: 0
# ERROR: 0
============================================================================