MockNC

MockNC (Mock-n-see) is a basic Mocking Framework for C to simplify unit testing. By leveraging function pointers, any function written through MockNC can be easily swapped out for another, redirecting all calls to your substituted function instead of the original.

How it works

Whereas normally code might look like:

Header

int MyFunc();

Source

int MyFunc()
{
    return 10*10;
}

Code written using MockNC would look like:

Header

MNC_DECLARATION(int, MyFunc, ())

Source

MNC_DEFINITION(int, MyFunc, ())
{
    return 10*10;
}

Which in the default configuration will just expand to output your code as normal!

Header

int MyFunc();

Source

int MyFunc()
{
    return 10*10;
}

Define a preprocessor variable called "MNC" however and then the magic happens:

Header

extern int(*MyFunc)();

Source

int MyFunc_Imp();
int (*MyFunc)() = MyFunc_Imp;
int MyFunc_Imp()
{
    return 10*10;
}

Which lets you

1. Call your function as you normally would
2. Swap out the implementation of your function at runtime

MyFunc(); //Returns 100
MyFunc = AlwaysReturn20;
MyFunc(); //Now returns 20

Extra Bits

Now, simply helping you swap the implementation behind a function is great and everything but it helps to have some extra tools!

MNC_SWAP and MNC_RESET

Using MNC_SWAP(identifier, new_target) and MNC_RESET() is a great combination when writing tests. Instead of manually tracking which functions are pointing where, one can simply reset the state of play at the start of each test:

    //Arrange
    MNC_RESET();
    MNC_SWAP(Get_Foo, Bar);

    //Act - Prove that Double_Foo() doubles the result from Bar()
    int result = Double_Foo();

    //Assert
    printf("%s\n", 18 == result ? "PASS" : "FAIL");

MNC_MOCK and MNC_VOID_MOCK

I get it, sometimes you just want to check that a function behaves correctly when it receives a certain return value when it calls another function or you just want to prove it's calling a function - this is what MNC_MOCK and MNC_VOID_MOCK can provide by helping take away the drudgery of writing your own code to handle this common task:

MNC_MOCK(int, Mock_Foo, ())

//Typical testing example, using a MockNC MOCK
void TestOne()
{
	//Arrange
	MNC_RESET();
	Mock_Foo.ReturnValue = 99;
	MNC_SWAP(Get_Foo, Mock_Foo.MockFunc);

	//Act - Prove Print_Foo() uses Get_Foo()
	Print_Foo();
	Print_Foo();
	Print_Foo();

	//Assert
	printf("%s\n", 3 == Mock_Foo.CallCount ? "PASS" : "FAIL");
}

MNC_VOID_MOCK(Mock_Log_Foo, ())

//Typical testing example, using a MockNC MOCK
void TestFour()
{
	//Arrange
	MNC_RESET();
	MNC_SWAP(Log_Access, Mock_Log_Foo.MockFunc);

	//Act - Prove Get_Foo() uses Log_Access()
	Get_Foo();

	//Assert
	printf("%s\n", 1 == Mock_Log_Foo.CallCount ? "PASS" : "FAIL");
}