cmake_minimum_required(VERSION 3.10)

# specify the C++ standard
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED True)

# set the project name and version
project(Tutorial VERSION 1.1)

option(USE_MYMATH "Use tutorial provided math implementation" ON)

if (USE_MYMATH)
  # add the MathFunctions library
  add_subdirectory(MathFunctions)
  list(APPEND EXTRA_LIBS MathFunctions)
#  list(APPEND EXTRA_INCLUDES "${PROJECT_SOURCE_DIR}/MathFunctions")
endif()

# add the executable
add_executable(Tutorial tutorial.cxx)

configure_file(TutorialConfig.h.in TutorialConfig.h)

target_link_libraries(Tutorial PUBLIC ${EXTRA_LIBS})

# add the binary tree to the search path for include files
# so that we will find TutorialConfig.h
target_include_directories(Tutorial PUBLIC
                           "${PROJECT_BINARY_DIR}"
                           )

install(TARGETS Tutorial DESTINATION bin)
install(FILES "${PROJECT_BINARY_DIR}/TutorialConfig.h"
  DESTINATION include
)

enable_testing()

# does the application run
add_test(NAME Runs COMMAND Tutorial 25)

# does the usage message work?
add_test(NAME Usage COMMAND Tutorial)
set_tests_properties(Usage
  PROPERTIES PASS_REGULAR_EXPRESSION "Usage:.*number"
  )

# define a function to simplify adding tests
function(do_test target arg result)
  add_test(NAME Comp${arg} COMMAND ${target} ${arg})
  set_tests_properties(Comp${arg}
    PROPERTIES PASS_REGULAR_EXPRESSION ${result}
    )
endfunction(do_test)

# do a bunch of result based tests
do_test(Tutorial 4 "4 is 2")
do_test(Tutorial 9 "9 is 3")
do_test(Tutorial 5 "5 is 2.236")
do_test(Tutorial 7 "7 is 2.645")
do_test(Tutorial 25 "25 is 5")
do_test(Tutorial -25 "-25 is [-nan|nan|0]")
do_test(Tutorial 0.0001 "0.0001 is 0.01")

../Step2/tutorial.cxx

#include <iostream>
#include <string>
#include <cstdlib>
#include "TutorialConfig.h"

#ifdef USE_MYMATH
#  include "MathFunctions.h"
#else
#  include <cmath>
#endif

int main(int argc, char *argv[]) {
  double inputValue = 0;
  if (argc < 2) {
    std::cout << "Usage: "<< argv[0] << "number\n";
    return 0;
  }
  inputValue = atof(argv[1]);

#ifdef USE_MYMATH
  const double outputValue = mysqrt(inputValue);
#else
  std::cout << "System cmath\n";
  const double outputValue = sqrt(inputValue);
#endif
  std::cout << "sqrt " << inputValue << " is " << outputValue << "\n";
}

add_library(MathFunctions mysqrt.cxx)

target_include_directories(MathFunctions
  INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}
  )

install(TARGETS MathFunctions DESTINATION lib)
install(FILES MathFunctions.h DESTINATION include)

#ifndef MATH_FUNCTIONS
#define MATH_FUNCTIONS

#define NaN 0

double mysqrt(double c);

#endif

#include "MathFunctions.h"

double abs(double x) {
  if (x >= 0) {
    return x;
  }
  return 0-x;
}

double mysqrt(double c) {
  if (c < 0) {
    return NaN;
  }
  double err = 1e-15;
  double t = c;
  while (abs(t - c/t) > err * t) {
    t = (c/t + t) / 2.0;
  }
  return t;
}

mkdir Step2_build
cd Step2_build
cmake ../Step2
make install
make test