to be rejected with

  • <Promise> to be rejected with <any>

Asserts that a promise is rejected with a specific reason (error):

var promiseThatWillBeRejectedWithAReason = new Promise(function(
  resolve,
  reject
) {
  setTimeout(function() {
    reject(new Error('Oh dear'));
  }, 10);
});
 
return expect(
  promiseThatWillBeRejectedWithAReason,
  'to be rejected with',
  new Error('Oh dear')
);

The expected reason will be matched against the rejection reason with to satisfy semantics, so you can pass any of the values supported by to satisfy:

var promiseThatWillBeRejectedWithAReason = new Promise(function(
  resolve,
  reject
) {
  setTimeout(function() {
    reject(new Error('Oh dear'));
  }, 10);
});
 
return expect(
  promiseThatWillBeRejectedWithAReason,
  'to be rejected with',
  /dear/
);

You get a nice diff if the assertion fails:

var promiseThatWillBeRejectedWithAReason = new Promise(function(
  resolve,
  reject
) {
  setTimeout(function() {
    reject(new Error('Oh dear'));
  }, 10);
});
 
return expect(
  promiseThatWillBeRejectedWithAReason,
  'to be rejected with',
  new Error('bugger')
);
expected Promise to be rejected with Error('bugger')
  
expected Error('Oh dear'to satisfy Error('bugger')
 
Error({
  
message
'Oh dear'
 
//
//
//
//
 
should equal 
'bugger'
 
Oh dear
bugger
})