How to return based on actual arguments being sent?

Let’s say we have a function with two arguments. It’s being called many times with different arguments on every call. So, its impossible to stub it with withArgs option.

async function foo(args1, args2){
    // some business logic
    return result
}

I want to write a stub function which will check the actual arguments being passed (args1, args2) and return a static response with a switch case. Something on the following lines:

sinon.stub(TestModule, "foo")
    .resolves(asyn function(args1, args2){
         switch(args2){
           case "a":
               return 1
           case "b":
               return 2
           case "c":
               return 3
           default: 
               return 0 
         }
         
     })

So, how to return based on actual arguments?

Answer

You can use stub(obj, 'meth').callsFake(fn) to dynamically check what passed in and response to it.

An example would be:

const mockFunction = (arg1, arg2) => { switch(arg2) {case "a": return 1 ...}}
sinon.stub(TestModule, "foo").callsFake(mockFunction);

Note that for an earlier version of Sinon < 3.0.0 You should use var stub = sinon.stub(object, "method", fn); instead.