javascript - Chai - expect function to throw error -

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• mocha / chai expect.to.throw not catching thrown errors 4 answers

i'm quite new chai i'm still getting grips things.

i have written function check api response , return either correct messaging or throw error.

networkdatahelper.prototype.formatpostcodestatus = function(postcodestatus) {  if (postcodestatus.hasownproperty("errorcode")) {     //errorcode should "invalid_postcode"     throw error(postcodestatus.errorcode); }  if (postcodestatus.hasownproperty("lori")) {     return "there appears problem in area. " + postcodestatus.lori.message; }  else if (postcodestatus.maintenance !== null) {     return postcodestatus.maintenance.bodytext; }  else {     return "there no outages in area."; } }; 

i've managed write tests messaging, however, i'm struggling error test. here's i've written date:

var networkdatahelper = require('../network_data_helper.js');  describe('networkdatahelper', function() { var subject = new networkdatahelper(); var postcode;      describe('#formatpostcodestatus', function() {         var status = {             "locationvalue":"sl66dy",             "error":false,             "maintenance":null,         };          context('a request incorrect postcode', function() {             it('throws error', function() {                 status.errorcode = "invalid_postcode";                 expect(subject.formatpostcodestatus(status)).to.throw(error);             });         });     }); }); 

when run test above, following error message:

1) networkdatahelper #formatpostcodestatus request incorrect postcode throws error: error: invalid_postcode

it seems error being thrown causing test fail, i'm not sure. have ideas?

with caveat i'm no chai expert, construct have:

expect(subject.formatpostcodestatus(status)).to.throw(error); 

cannot possibly handle thrown exception before chai framework gets around seeing .to.throw() chain. code above calls function before call expect() made, exception happens soon.

instead, should pass function expect():

expect(function() { subject.formatpostcodestatus(status); })   .to.throw(error); 

that way, framework can invoke function after it's prepared exception.