Is it possible to mock a function imported from a package in golang?

Question

I have the following method to test, which uses a function imported from a package.

import x.y.z  func abc() {     ...     v := z.SomeFunc()     ...  } 

Is it possible to mock SomeFunc() in golang?

Answer 1

Yes, with a simple refactoring. Create a zSomeFunc variable of function type, initialized with z.SomeFunc, and have your package call that instead of z.SomeFunc():

var zSomeFunc = z.SomeFunc  func abc() {     // ...     v := zSomeFunc()     // ... } 

In tests you may assign another function to zSomeFunc, one that is defined in tests, and does whatever the test wants it to.

For example:

func TestAbc(t *testing.T) {     // Save current function and restore at the end:     old := zSomeFunc     defer func() { zSomeFunc = old }()      zSomeFunc = func() int {         // This will be called, do whatever you want to,         // return whatever you want to         return 1     }      // Call the tested function     abc()      // Check expected behavior } 

See related / possible duplicate: Testing os.Exit scenarios in Go with coverage information (coveralls.io/Goveralls)