Purpose (TL;DR) - mandatory

Fixes #2496 by cleaning any previous exception* behavior when callsFake is used.

Background (Problem in detail)

• Issue throws() keeps raising exception with callsFake() #2496

Precedence among behaviors is defined by the behavior itself (cleaning other previously set behaviors) and by the order at invocation time.

Since throws behavior (exception and exceptionHandler) is the first one to run at invocation time, other behaviors can only define precedence on its own definition. That's why I modified callsFake behavior to clean throws

Solution

When callsFake is chained on a stub it cleans previous exception and exceptionHandler values which essentially invalidates any previous throws or throwsException behaviours.

Note: I think this fix should not break any current usage, because any attempt to run the stubbed function would have raised an exception already and the developer would have noticed the same I did notice: callsFake was ignored, so that, probably they applied some workaround like restoring + callsFake OR recreating the stub + callsFake.

How to verify - mandatory

Run:

const fn = sinon.stub().throws('not mocked');
fn.callsFake(() => 'mocked behavior')

console.log(fn())

You should see:

mocked behavior

Checklist for author

• npm run lint passes
• n/a References to standard library functions are cached.