General reference: GoogleTest Primer.

Installation details are in the README. To sum up:

$ mkdir mybuild       # Create a directory to hold the build output.
$ cd mybuild
$ cmake ${GTEST_DIR}  # Generate native build scripts.
$ make
$ cp libgtest.a /usr/local/lib
$ cp libgtest_main.a /usr/local/lib

A bare minimum google test is:

#include <gtest/gtest.h>

TEST(MathTest, TwoPlusTwoEqualsFour) {
  EXPECT_EQ(2 + 2, 4);
}

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

and compiles with

g++ -I ${GTEST_DIR}/include/ mytest.cpp ${LIBRARIES} -lpthread -o a.out

Wrapping up everything in a nice makefile yields:

TARGET = network
TEST = check
CC = g++
CFLAGS = -g -Wall
LIBS = -lpthread

DEPS = file1.h file2.h
OBJ = file1.o file2.o

GTEST = gtest-1.7.0/include
LIBGTEST = /usr/local/lib/libgtest_main.a /usr/local/lib/libgtest.a
TESTDIR = tests

%.o: %.cpp $(DEPS)
	$(CC) -c -o $@ $< $(CFLAGS)

$(TARGET): $(OBJ) main.o
	$(CC) -o $@ $^ $(CFLAGS)

$(TEST): $(OBJ)
	$(CC) -o $@ $^ $(CFLAGS) -I $(GTEST) $(TESTDIR)/*.cc $(LIBGTEST) $(LIBS)
	./$(TEST)

clean:
	rm -rf *.o *.gch
	rm -f $(TARGET) $(TEST)