使用功能进行Golang测试

Question

I am using a third-party library that is a wrapper over some C functions. Unfortunately, nearly all of the Go functions are free (they don't have a receiver, they are not methods); not the design approach I would have taken but it is what I have.

Using just Go's standard "testing" library:

Is there a solution that allows me to create tests where I can mock functions?

Or is the solution to wrap the library into structures and interfaces, then mock the interface to achieve my goal?

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I have created a monte carlo simulation that also process the produced dataset. One of my evaluation algorithms looks for specific models that it then passes the third-party function for its evaluation. I know my edge cases and know what the call counts should be, and this is what I want to test.

Perhaps a simple counter is all that is needed?

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Other projects using this library, that I have found, do not have full coverage or no testing at all.

Answer 1

You can do this by using a reference to the actual function whenever you need to call it.

Then, when you need to mock the function you just point the reference to a mock implementation.

Let's say this is your external function:

// this is the wrapper for an external function
func externalFunction(i int) int {
   return i * 10  // do something with input
}

You never call this directly but instead declare a reference to it:

var processInt func(int) int = externalFunction

When you need to invoke the function you do it using the reference:

fmt.Println(processInt(5))

Then, went you want to mock the function you just assign a mock implementation to that reference:

processInt = mockFunction

This playground puts it together and might be more clear than the explanation:

https://play.golang.org/p/xBuriFHlm9

If you have a function that receives a func(int) int, you can send that function either the actual externalFunction or the mockFunction when you want it to use the mock implementation.