Support custom messages for assertions

[jfairbank]

Most assertions libraries allow you to specify a custom message/label as the last argument. This is tricky for test plan because some effect assertions like call take variable number of arguments. What might work best is an additional method that allows you to set a custom message for the next assertion, or an additional function on each effect assertion.

Something like this:

testSaga(mainSaga)
  .next()
  .labeledAssertion('hello world')
  .call(identity, 41);

// SagaTestError:
// Assertion 1 failed: call effects do not match
// hello world
// 
// Expected
// --------
// { context: null, fn: [Function: identity], args: [ 41 ] }
// 
// Actual
// ------
// { context: null, fn: [Function: identity], args: [ 42 ] }

Or something like this:

testSaga(mainSaga)
  .next()
  .call.labeled('hello world', identity, 41);

// SagaTestError:
// Assertion 1 failed: call effects do not match
// hello world
// 
// Expected
// --------
// { context: null, fn: [Function: identity], args: [ 41 ] }
// 
// Actual
// ------
// { context: null, fn: [Function: identity], args: [ 42 ] }

Other suggestions and ideas are welcome.

[TzviPM]

is it possible to call something that's not a function in redux-saga? Perhaps we could just check if the first argument is a function or a string?

[jfairbank]

Hi, @omniroot. Thanks for the suggestion, but unfortunately, that wouldn't work for other assertions like take which actually can take a string as the first argument. We could create a function that creates a special object for messages via a helper function, but I'm not a big fan of that.

testSaga(mainSaga)
  .next()
  .call(identity, 41, assertionMessage('hello world'));

I'm still leaning toward either of the former ideas I proposed, but this feature has been low priority compared to other features at the moment.

[0xdevalias]

How about using Symbol()? Iterate over the params (or take the last one), and only if it matches the Symbol, treat it as a message.

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol

Edit: Which reading properly.. is similar to your above wrapping function method..