CppUTest Example

This is an example about using CppUTest to mock C files for unit test.

Prerequisites

CMake
GNU C/C++ compiler

Directory Structure

cpputest_example
├── CMakeLists.txt                     --> main cmake configuration file
├── LICENSE
├── readme.md
├── src                                --> pythagorean example
│   ├── CMakeLists.txt
│   ├── main.c
│   ├── pythagorean.c                  --> unit under test
│   ├── pythagorean.h
│   ├── square_root.c                  --> dependency of pythagorean.c
│   └── square_root.h
└── tests                              --> unit test against pythagorean.c
    ├── CMakeLists.txt
    ├── cpputest_common.cmake
    ├── cpputest_external_proj.cmake   --> cmake configuration file to build CppUTest 
    │                                      and CppUMock as an external project.
    └── pythagorean_ut                 --> unit test using CppUTest and CppUMock
        ├── CMakeLists.txt
        ├── main.cpp
        ├── pythagorean_ut.cpp
        └── square_root_mock.cpp

Unit Test

The src folder contains the source code of an example called cpputest_example_pythagorean after it is built by CMake.

pythagorean.c implements a function called Pythagorean_hypotenuse(x, y), which calculates the hypotenuse of a right-angled triangle with x and y as the two sides of right angle.
square_root.c provides a function called SquareRoot_sqrt(number), which returns the square root of the parameter number.
The implementation of Pythagorean_hypotenuse(x, y) calls SquareRoot_sqrt(number). That is, Pythagorean_hypotenuse(x, y) depends on SquareRoot_sqrt(number).

We want to test Pythagorean_hypotenuse(x, y) function provided by pythagorean.c. From the unit test point of view, Pythagorean_hypotenuse(x, y) is the System Under Test (SUT), SquareRoot_sqrt(number) is its dependency.

Test 1 - Simple Test

TEST(Pythagorean, simpleTest)
{
    // arrange
    mock().expectOneCall("SquareRoot_sqrt")// expect Pythagorean_hypotenuse(...) call SquareRoot_sqrt(...).
          .withParameter("number", 25.0)   // bubble 2 - expect the number is passed as 25.0,
                                           // because 3.0^2 + 4.0^2 is 25.0.
          .andReturnValue(5.0f);           // bubble 3 - return the result as 5.0f,
                                           // because square root of 25.0 is 5.0.

    // act
    float hypotenuse = Pythagorean_hypotenuse(3.0, 4.0); // bubble 3, 4

    // assert
    mock().checkExpectations();
    CHECK_EQUAL(5.0f, hypotenuse);
}

Test 2 - Black Box Test

TEST(Pythagorean, BlackBoxTest)
{
    // arrange
    mock().expectOneCall("SquareRoot_sqrt")// expect Pythagorean_hypotenuse(...) call SquareRoot_sqrt(...).
          .withParameter("number", 100.0)  // bubble 2 - expect the number is passed as 100.
                                           // because 6.0^2 + 8.0^2 is 100.0.
          .andReturnValue(100.0f);         // bubble 3 - intentionally set the result as 100.0 instead of 10.0.
                                           // we want to assure Pythagorean_hypotenuse(x, y) returns whatever SquareRoot_sqrt(number)` gives.

    // act
    float hypotenuse = Pythagorean_hypotenuse(6.0, 8.0); // bubble 3, 4

    // assert
    mock().checkExpectations();
    CHECK_EQUAL(100.0f, hypotenuse);
}

Building the example on Linux

~/cpputest_example (master)$ cmake -B build -G "Unix Makefiles"
-- The C compiler identification is GNU 7.5.0
-- The CXX compiler identification is GNU 7.5.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done
-- Generating done
-- Build files have been written to: /home/max/cpputest_example/build
~/cpputest_example (master)$ ls
CMakeLists.txt  LICENSE  build  readme.md  src  tests
~/cpputest_example (master)$ cd build
~/cpputest_example/build (master)$ make
Scanning dependencies of target CppUTest
...
...
...
[ 93%] Building C object src/CMakeFiles/cpputest_example_pythagorean.dir/main.c.o
[ 95%] Building C object src/CMakeFiles/cpputest_example_pythagorean.dir/pythagorean.c.o
[ 97%] Building C object src/CMakeFiles/cpputest_example_pythagorean.dir/square_root.c.o
[100%] Linking C executable cpputest_example_pythagorean
[100%] Built target cpputest_example_pythagorean

Test Result

~/cpputest_example/build $ ctest -V
...
test 1
    Start 1: pythagorean_test

1: Test command:
~/cpputest_example/code-build/tests/pythagorean_ut/pythagorean_ut.exe
1: Test timeout computed to be: 1500
1: 
1: SquareRoot_sqrt gets called with parameter: 100.000000.
1: .
1: SquareRoot_sqrt gets called with parameter: 25.000000.
1: .
1: OK (2 tests, 2 ran, 6 checks, 0 ignored, 0 filtered out, 0 ms)
1:
1/1 Test #1: pythagorean_test .................   Passed    0.09 sec

100% tests passed, 0 tests failed out of 1

Total Test time (real) =   0.15 sec

maxpeng/cpputest_example