Asserts that the function throws an error when called.

function willThrow() {
  throw new Error('The error message');
}
expect(willThrow, 'to throw');
expect(willThrow, 'to throw error');
expect(willThrow, 'to throw exception');

In case of a failing expectation you get the following output:

expect(function willNotThrow() {}, 'to throw');
expected function willNotThrow() {} to throw

You can assert the error message is a given string if you provide a string as the second parameter.

expect(function () {
  throw new Error('The error message');
}, 'to throw', 'The error message');

In case of a failing expectation you get the following output:

expect(function () {
  throw new Error('The error message!');
}, 'to throw', 'The error message');
expected
function () {
  throw new Error('The error message!');
}
to throw 'The error message'
  
expected Error({ message'The error message!' }) to satisfy 'The error message'
 
-
The error message!
+
The error message

By providing a regular expression as the second parameter you can assert the error message matches the given regular expression.

expect(function () {
  throw new Error('The error message');
}, 'to throw', /error message/);

In case of a failing expectation you get the following output:

expect(function () {
  throw new Error('The error message!');
}, 'to throw', /catastrophic failure/);
expected
function () {
  throw new Error('The error message!');
}
to throw /catastrophic failure/
  
expected Error({ message'The error message!' }) to satisfy /catastrophic failure/

You can also provide a function as the second parameter to do arbitrary assertions on the error.

expect(function () {
  this.foo.bar();
}, 'to throw', function (e) {
  expect(e, 'to be a', TypeError);
});

In case of a failing expectation you get the following output:

expect(function () {
  throw new Error('Another error');
}, 'to throw', function (e) {
  expect(e, 'to be a', TypeError);
});
expected
function () {
  throw new Error('Another error');
}
to throw
function (e) {
  expect(e, 'to be a', TypeError);
}
  
expected Error({ message'Another error' }) to be a TypeError

This assertion can be negated using the not flag:

expect(function () {
  // Do some work that should not throw
}, 'not to throw');

In case of a failing expectation you get the following output:

expect(function () {
  throw new Error('threw anyway');
}, 'not to throw');
expected
function () {
  throw new Error('threw anyway');
}
not to throw
  
threw: Error({ message'threw anyway' })