funcmock is a Function Mocking Framework in Go which replaces the lexical placeholder of the function with a mock. It is primarily intended to be used for testing purposes.

Using funcmock

Example:

package main

import "funcmock"

var funcToBeMocked = func(foo int, bar string) (int, float64) {
	// I am computation intensive, hence take long
	// Don't use me unnecessarily
	return 2, 2.3

}

func iUseFuncToBeMockedTenTimes() {

	for i := 0; i < 10; i++ {
		_, _ = funcToBeMocked(1, "qux")
	}
}

func main() {

	// The mock engine specific to a function
	funcMockEngine := funcmock.Mock(&funcToBeMocked)

	// call iUseFuncToBeMockedTenTimes which calls funcToBeMocked
	iUseFuncToBeMockedTenTimes() // actual funcToBeMocked is not called

}

Controller.CallCount() returns the number of times the function was called

 // call iUseFuncToBeMockedTenTimes which calls funcToBeMocked
 iUseFuncToBeMockedTenTimes() 	// actual funcToBeMocked is not called
 fmt.Println("Mock function called ", funcMockEngine.CallCount(), " times.")

will print Mock function called: 10

MockController.SetDefaultReturn sets default return of the calls to the mock function which are not preset. This function can only be called once. (This behavior, of being able to just call it once, can be expected to change in future)
MockController.Called() returns a bool indicating whether the mock function was ever called or not.
MockController.Restore() returns the function to its original version. Mock function cannot be brought back after calling this. Further call the function will not invoke the mock or update the logs associated with the call to the mocked function, and will invoke the original function.
MockController.NthCall() returns a call struct instance of the nth call to the mock function since the mock was constructed. Does not have to be already called.
call.SetReturn presets the return of a particular call of the mock function. (Of course, it should not have already been called, else it could not be of much use.)
call.Called() returns bool indicating whether a particular call to the mock function was made or not.
call.NthParam() returns the parameter that was used in a particular call to the mock function.
call.Return() its functionality is currently undecided. Returns instance of the same call, for now.